Part 3: Synthesis II: fish, early life, predation, wildlife and forest

The Hot Brook lakes of eastern Maine — part 3 of 5

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3. Maine lake ecosystems: a synthesis (continued)

3.5 The fish: community, life histories, energetics, seasonal habitat and movement

3.5.1 The regional fauna and the Hot Brook list

Maine has 69 freshwater fish species in 44 genera, 47 of them (about 70 %) native; the Downeast region holds 47 species, 41 of them native (MNAP, ch. 3, its Tables 3.2 and 3.4). Most of the non-natives are minnows and centrarchids. The state's review describes "a relentless homogenization of fish assemblages", with basses, black crappie, white perch and minnows still being moved, and links introduced littoral predators (both basses, chain pickerel, northern pike) to losses of minnow diversity (MNAP; Whittier et al. 1997). MDIFW classes yellow perch, white perch, chain pickerel, pumpkinseed, redbreast sunfish and brown bullhead as native to Maine and smallmouth bass, largemouth bass, black crappie, northern pike and muskellunge as introduced; pumpkinseed and redbreast are the state's only native centrarchids (MDIFW 2017). Statewide labels hide drainage histories. Chain pickerel "was apparently native to only the southwestern portion of Maine" and was moved through southern, central and eastern Maine in the nineteenth century, from the Penobscot to the St. Croix in the early 1800s among other transfers (Brokaw 2001). The pre-settlement range of white perch "is not known", although it was "quite likely" present in all major drainages up to the first barrier (Smith 2002). Smallmouth bass were stocked into five drainages, the St. Croix among them, in 1868–1881 (Everhart 1966 and Warner 2005, via Smithsonian NEMESIS). The Penobscot diadromous-fish plan lists chain pickerel as native in its Table 4 but as introduced to the Penobscot drainage in its text, and calls white perch "introduced throughout the drainage" (Maine DMR & MDIFW 2008).

MDIFW's non-sport plan lists white sucker in 1,206 Maine lakes, yellow perch in 818, American eel in 683, fallfish in 461, blacknose dace in 436, banded killifish in 363 and sea-run alewife in 102 (Kramer 2002); white perch occur in 514 waters (Smith 2002), chain pickerel in 781 (Brokaw 2001) and smallmouth bass in 517 surveyed lakes, 84 of them in the Penobscot region (MDIFW 2021). In a random sample of 203 northeastern lakes (EMAP, 1991–96) the share of lakes holding each species was pumpkinseed 74 %, yellow perch 72 %, golden shiner 71 %, brown bullhead 69 %, white sucker 56 %, chain pickerel 45 %, smallmouth 31 %, banded killifish 26 %, white perch 19 %, American eel 19 % and redbreast 14 % (Whittier et al. 1999, 2000, 2001; abstracts only).

The 1949 MDIFW surveys of both lakes (revised 1965 and 2004) list the same nine species — smallmouth bass, white perch, yellow perch, chain pickerel, bullhead ("hornpout"), banded killifish, blacknose dace, fallfish and white sucker — and name smallmouth bass, white perch and chain pickerel as the principal fisheries (MDIFW 1949). MDIFW's lake database adds pumpkinseed for Upper (MDIFW 2007, Lake Fish of Maine), and the 2024 depth chart of Lower lists pumpkinseed and sea-run alewife (MDIFW 2024). Redbreast sunfish appears in no MDIFW record: it rests on angler observations (project field notes), in which most of the sunfish kept from the connecting brook were identified by photograph as redbreast. Golden shiner, common shiner and American eel appear in none of the records, and the angler has seen neither golden shiner nor eel; golden shiner, common in the region, is not treated here as a Hot Brook fish. Among 17 regional lakes that hold smallmouth bass, white perch and chain pickerel, recorded richness averaged 13.9 species, and 10.7 in the seven shallow (≤ 8 m) ones, against 10 species recorded for Upper and 9 for Lower; American eel (14 of 17 lakes), rainbow smelt (11) and brook trout (10) are the commonest species of those lakes missing from Hot Brook's list (project tally of MDIFW 2007). Which species are native to these lakes is undocumented: smallmouth bass are introduced, chain pickerel probably are, white perch is uncertain, and the remaining species are probably native (project inference); the state's non-native-fish layer marks both lakes "confirmed" without naming species.

3.5.2 Relative abundance, density and standing crop

No census was found for any eastern Maine lake with Hot Brook's bass, white perch and pickerel, and no record of netting, electrofishing, creel survey, age–growth sampling or stocking has been found for either Hot Brook lake (MDIFW stocking reports 2015–2025; project searches). Relative abundance therefore comes from nearby lakes. In nine eastern Maine lakes 32–94 km from Hot Brook, sampled once in midsummer with trap nets, gill nets, minnow traps and seines (EMAP, 1991–94), the median shares of adult fish were white perch 42 % (55–68 % in the lakes most like Hot Brook, with white perch, bass and pickerel), white sucker 7 %, yellow perch 6 %, pumpkinseed 5 %, brown bullhead 3 %, smallmouth 2 %, golden shiner 1.3 %, fallfish 0.9 %, banded killifish 0.5 % and chain pickerel 0.5 %; the median ratio of adult white perch to adult smallmouth in the six lakes holding both was about 18:1, and young yellow perch far outnumbered adults (East Branch Lake: 577 juveniles and 331 young of the year against 45 adults) (EMAP data; project tally, made by a fetch tool's summarizer rather than a script). Night boat electrofishing in nine Connecticut lakes holding smallmouth (≥ 5 per hour), white perch and chain pickerel gave median catches per hour of 42 white perch, 30 pumpkinseed, 16 redbreast, 12 yellow perch, 8 smallmouth, 7 white sucker, 6 chain pickerel and 2 brown bullhead (CT DEEP 2018; ± 20 % from misaligned rows); electrofishing favors sunfish and bass and nets favor white perch, so the two methods agree mainly in placing white perch first. Maine's 1940 survey of 53 southern lakes caught 1,627 white perch in 86 gill-net sets against 388 white suckers, 226 yellow perch and 117 pumpkinseed, and found white perch "more abundant in the shallow lakes": 62–128 per 24-h set in four shallow unstratified lakes against 7–46 in most deep ones (Cooper 1941).

The only Maine whole-lake counts are Rupp & DeRoche's (1965) rotenone censuses of three small, soft-water lakes being reclaimed for trout (Table 3.5-1). Snorkel and SCUBA pickup showed how much ordinary rotenone counts miss: at Shagg 40 % of the fish by weight and 52 % by number sank in water deeper than 3 m (smelts mostly sank, suckers and pickerel mostly floated), so its crop of 44.5 kg/ha is a minimum; the 90 % confidence limits at the other two lakes were about ± 24 %. The three lakes are deeper and probably less productive than Hot Brook, and Coleback lacked white and yellow perch and bass, but they give the only Maine per-species numbers: chain pickerel at 83 and 175 fish/ha (4.1 and 8.4 kg/ha), white sucker at 236–275/ha (24.5–38.4 kg/ha), and American eel making up 41 % of fish weight in a Washington County lake. Michigan's survey of 64 lakes and ponds bracketed whole-lake crops at 11–404 kg/ha, with "normal" lakes near 99 kg/ha and soft-water lakes often only 11–70 kg/ha, and piscivores made up about 10–21 % of fish biomass in eight of the lakes, all with bass (Schneider 1973b; piscivore shares are project arithmetic on Schneider's tables). An estimate of Maine's statewide white perch stock, 60,175,000 fish and 10,590,800 lb (Jordan 1981, quoted in Stanley & Danie 1983), spreads to about 261 fish/ha and 20.8 kg/ha over the state's white perch acreage (project arithmetic); a 2008 University of Maine thesis put East Pond (Belgrade, eutrophic) at 174,000 ± 11,000 white perch, about 236/ha, size threshold unstated (relayed by a search summary; unverified). MDIFW's stock objective for smallmouth bass longer than 25 cm, 2.0 fish/acre and 2.3 lb/acre (4.9/ha, 2.6 kg/ha) over usable habitat, was met statewide (Jordan 2001). No chain pickerel density was found for any northeastern lake outside Rupp & DeRoche's; MDIFW says only that pickerel maintain "moderate to high density populations" wherever shallow weedy habitat exists (Brokaw 2001). No per-area density was found for fallfish anywhere, and the only banded killifish count found is from the shallows of two Newfoundland ponds (about 20,600 fish in August; Chippett 2004, via COSEWIC 2014).

Table 3.5-1. Whole-lake and species densities in Maine lakes and northern analogs, in fish per hectare and kg/ha; Maine values first. Rupp & DeRoche's per-acre values and the lake areas and depths are converted by the project.

3.5.3 Life histories

Tables 3.5-2 and 3.5-3 collect growth, maturity, fecundity, spawning, longevity, diet, tolerances and bioenergetic parameter sets, Maine values first. Maine provides almost no age-based data: there is no Maine length-at-age table for yellow perch, pumpkinseed, redbreast, fallfish or bullhead, and the white perch growth data come from southern Maine lakes in 1938–40. Early life and recruitment are treated in section 3.6 and predation as a process in section 3.7.

Table 3.5-2. Growth, maturity and reproduction of the Hot Brook fishes (total length unless stated; "via" marks a value known second-hand).

Table 3.5-3. Longevity, diet, tolerances and Fish Bioenergetics 4.0 (FB4) parameter sets. UILT = upper incipient lethal temperature; M = instantaneous natural mortality; A = annual mortality.

Yellow perch, among the most widespread species of the region's lakes, is scarce at Hot Brook: the angler finds "few perch even ice fishing or with small baits", small ones, and fewer than fallfish and bass (angler observations, project field notes), and the lakes are not among the waters open to commercial yellow perch harvest in MDIFW's 2014 permit file, which lists several nearby lakes, weak evidence from an absence. Maine's fishery agency "has spent more time and effort at eliminating yellow perch populations than … managing them" (Kramer 2002). Crowded perch stunt: in Michigan single-species perch lakes, very large year classes "stopped growing at a length of 4–5 inches" (10–13 cm) once they had depleted the benthos (Schneider 1972; relayed by a search summary), and faster-growing stocks mature younger but at larger sizes (Feiner et al. 2017). Smallmouth bass "grow slowly in Maine" (MDIFW species page), and in many Maine waters populations consist "primarily of fish from 8–13 inches" (20–33 cm) because spawning habitat is abundant and juvenile bass have few predators; cool summers in 1986, 1992 and 1996 caused "large-scale reductions of those cohorts" (Jordan 2001), a first-winter bottleneck treated in section 3.6. Chain pickerel in Maine are angled mostly at ages 3–5 and 36–48 cm (MDIFW 2017), and "many pickerel ponds support good numbers of 15–19 inch fish" (Brokaw 2001), but no catch-curve, tagging or mark–recapture survival estimate for the species in a northeastern lake was found, and an estimate from age frequencies in two Rhode Island ponds (Saila 1956) was not obtained.

The two sunfishes divide by habitat. Pumpkinseed is a lake fish of weedy margins whose larger individuals crush snails (Mittelbach 1984; Cooper 1941). Redbreast is the stream sunfish of the Northeast, "typically common in rivers and large streams and uncommon to rare in lakes", "not typically associated with vegetation" and more tolerant of current than other sunfishes (CT DEEP species page). Its northernmost known population, in Yoho Lake, New Brunswick (131 ha, mean depth 3.7 m), numbered only 325–744 fish by Petersen estimate, and its oldest age class (6+) averaged 16 cm (Gautreau & Curry 2012). The 18–21-cm redbreast the angler catches in the connecting brook (angler observations, project field notes) would weigh about 110–180 g by Yoho's length–weight relation and, at Yoho growth, be at least 7–10 years old (project estimate), older than any aged northern redbreast; either they grow faster than at Yoho or the brook holds old fish. White sucker and brown bullhead are long-lived benthic fishes that nets catch mostly as adults (section 3.5.5). Spring-run trap nets catch little else: white suckers were 96 % of the trap-net catch during the spring run in a Unity College study (Kramer 2002), and Maine reference lakes held larger, older suckers than harvested lakes, where annual mortality was at least twice as high (Begley, Coghlan & Zydlewski 2017, abstract). Bullheads, with golden shiners, survived the lowest oxygen in Michigan winterkills (Cooper & Washburn 1946), and most published bullhead studies concern "overcrowded and stunted populations" (Rubec 1975, citing Carlander 1969).

The three small, probably native species have distinct homes. Banded killifish is "typically a lake fish … on extensive lake shallows" (Cooper 1941), schooling in very shallow water over sand near plants (CT DEEP species page; relayed by a search summary); blacknose dace is "typically a stream fish" of pools and gravel riffles in small streams, rarely found in lakes (Cooper 1941; Trial et al. 1983b); fallfish, the second commonest minnow in Cooper's survey, lives in both, and in the Maine Cooperative Fishery Research Unit's observations "fallfish move from larger waters into streams to spawn" (Trial et al. 1983a). Small-bodied fish are the members of the community most sensitive to piscivores: Adirondack lakes with northern pike or bass held about a third of the native minnow richness of lakes without them (Findlay, Bert & Zheng 2000, abstract); small Ontario lakes with smallmouth held 2.3 fewer small-bodied species (MacRae & Jackson 2001); and three Nova Scotia lakes invaded by chain pickerel held only pickerel and large white suckers, with no small-bodied species, although their pre-invasion communities are unknown (Mitchell, LeBlanc & Heggelin c. 2011).

Sea-run alewives reached Danforth by natural straying, confirmed by Maine DMR in 2017 and described as "the farthest inland known to recolonize naturally on the East Coast"; a fishway on Baskahegan Stream at Danforth was built in 2023 (ASF 2021, 2024). The 2024 MDIFW chart of Lower is the only record of alewives in the lakes, and no count exists; the state's alewife-habitat layer, of unstated date, still marks both lakes "inaccessible – not stocked". The Penobscot plan's potential of 235 adults per acre — 214,320 for Upper and 167,555 for Lower — is a planning figure derived from commercial yields in six Maine watersheds (1971–83), and the plan warns that oligotrophic Penobscot lakes "may not produce" it (Maine DMR & MDIFW 2008; Maine DMR 2024). Adults stay in Maine lakes for weeks and a large share die there (Table 3.5-3); the young leave between mid-July and early December and cannot overwinter in their natal lakes (Kircheis, Trial, Boucher et al. 2002; McCormick et al. 1997, via Gahagan, Gherard & Schultz 2010). Stocking at six adults per acre into Lake George, Maine changed the zooplankton but not the size of the resident smallmouth, pickerel, white perch, yellow perch, pumpkinseed, redbreast or bullhead (Kircheis, Trial, Boucher et al. 2002). The alewife's effects on plankton, nutrients and predators belong to sections 3.2, 3.3, 3.6 and 3.8.

American eel is recorded in 761 of 2,207 Maine lakes in MDIFW's database (34 %), in 14 of the 17 regional analog lakes and in Baskahegan Lake and Crooked Brook Flowage upstream on the same stream, but not at Hot Brook (MDIFW 2007; project tally), and the angler has never seen one (angler observations, project field notes). Where present eels can dominate fish biomass (41 % at Coleback; Rupp & DeRoche 1965), but daytime nets and seines probably miss them (project inference); baited eel traps around Pennamaquan Lake (Washington Co.) took 69 yellow eels in 2017, 7.7 % of the catch (Johnson 2018). The ≈ 204-km route to the sea (project measurement on NHDPlus flowlines) passes the Milford and West Enfield dams, both with upstream eel passage; telemetered silver eels survived at 0.966–0.984 per river km through dammed sections against 0.998 in free river (Mensinger, Blomberg & Zydlewski 2021, abstract), about 0.78 through both dams (project estimate). Whether eels live in the lakes is unknown.

3.5.4 Energetics: the FB4 parameter sets and the winter

Fish Bioenergetics 4.0 (Deslauriers et al. 2017; FB4 parameter file) holds parameter sets for only three of the eleven Hot Brook species — yellow perch, smallmouth bass and brown bullhead — plus alewife; none exists for pumpkinseed, redbreast, chain pickerel, white perch, white sucker, fallfish, banded killifish or blacknose dace, the only Lepomis set is bluegill and the only Moronidae are striped and white bass (FB4 file; fb4package vignette). Even the existing sets are weak for these lakes. The yellow perch models mis-estimated resting metabolism in a laboratory test, with growth errors tracking feeding rate (Bajer, Whitledge, Hayward & Zweifel 2003, abstract). The brown bullhead set is documented only in conference work (no peer-reviewed paper was found), on fish of 2.5–131 g at 10–30 °C (Hartman et al. 2017; AFS 2011 poster). The Whitledge et al. (2003) smallmouth set's respiration was measured only at 18–30 °C, on Missouri fish (via Brownscombe, Smith & Bzonek 2024); its weight exponent (RB −0.756, about three times the usual slope) gives a negative energy budget at maximum ration for a 5-g fish at every temperature and a break-even size of about 10 g at 20 °C and 20–25 g at 15 and 25 °C, so it is usable only above about 30 g (project arithmetic). The Shuter & Post (1990) row as stored in FB4 gives negative growth at full ration at every size and temperature tested (5 and 100 g at 10–30 °C); Minnesota's Mille Lacs model used RA 0.009 rather than the stored 0.03, which suggests a unit error (Ahrenstorff & Holbrook 2016; project hypothesis). Surrogates carry their own biases: the bluegill set predicts 20–70 % more respiration than was measured in 30-g pumpkinseed at 5–25 °C (Roberts 1964, via Altman & Dittmer 1971 and FishBase; project arithmetic, one study of unknown acclimation), and the esocid model used for pickerel overestimates consumption, especially in winter and at low ration (Chipps et al. 2000, abstract, on age-0 tiger muskellunge), by 39–52 % in young-of-year esocids stocked in Ohio reservoirs (Wahl & Stein 1991, abstract). Computed from the stored curves, a 100-g perch or pike can still eat 1–2 % of its body weight a day at 4 °C, a bass only 0.3–0.5 % (project arithmetic).

Winter, about 208 days below 10 °C at Spednic Lake in Washington County (Dudley & Trial 2014), is where the sets diverge most from field evidence, and the species spend it differently. Yellow perch keep feeding and roughly hold their lipid (Sullivan 1986, abstract); in Lake Champlain's Keeler Bay 34 % of perch stomachs were empty in winter against 8–10 % in spring and summer and the fish grew, while pumpkinseed ate rarely and lost lipid and condition; modeled summer-peak consumption was 6.0 times February's in perch and 10.6 times in pumpkinseed (Block et al., draft manuscript). Pumpkinseed cooled to about 2.5 °C were minimally active at ≤ 7.9 °C and stopped feeding at ≤ 4 °C, with no metabolic depression beyond the ordinary temperature effect (Reeve, Rowsey & Speers-Roesch 2022). Smallmouth bass are quiescent rather than dormant in winter: in Lake Opeongo they made the year's largest energy gain in autumn and fed little in winter (Suski & Ridgway 2009), and males' muscle lipid in autumn was about 1.5 times that of spring and visceral lipid more than twice (Mackereth, Noakes & Ridgway 1999), implying that about half of autumn lipid is spent between October and May (project arithmetic). No measurement of adult smallmouth winter mass loss was found. The closest analog, largemouth bass in an Ontario lake that holds yellow perch, pumpkinseed, brown bullhead, golden shiner and white sucker, lost 3.6 ± 1.4 % of mass between November and June, and fasting simulations predicted 12–28 % losses against 8.9 % observed in 11 fish (Reeve, LaRochelle, Bihun, Brownscombe & Cooke 2025). Swim-tunnel resting metabolism of a 1-kg smallmouth extrapolates to 61–78 mg O₂ kg⁻¹ h⁻¹ at 2–8 °C (Brownscombe, Smith & Bzonek 2024; extrapolation by the project), but a fasting adult at such rates for 150 days would burn about 60 % of its body energy; field depletion fits 15–30 mg O₂ kg⁻¹ h⁻¹ at 2–6 °C (project inference). Northern pike clear a meal in 48 h in summer but 12 days in winter and eat very little under ice, while females build most of their ovaries in winter (Diana 1979b, 1983, abstracts); no energetic measurement was found for chain pickerel, which also feed under Maine ice (section 3.5.6). Brown bullheads bury themselves in leafy ooze and stop feeding (Wisconsin DNR 2008), and did not feed at all in a 2 °C Connecticut pond (Massengill 1973, via Ellman 2023).

Parental care is the other energetic bottleneck of the nest-guarding species. By model, a 354–926-g smallmouth guarding for 22 days at 18 °C without food would lose 11.8–16.2 % of its mass (Cooke, Philipp & Weatherhead 2002), but guarding males do feed — 60–100 % had gut contents at each brood stage in Lake Opeongo (Mackereth, Noakes & Ridgway 1999) — and lost little there (585 to 571 g in 19 days) against 11.5 % in Lake Erie, where hyperabundant invasive round gobies raised the males' chase rate ninefold (Steinhart et al. 2005); no field study that was found reports a guarding male starving to death (project review; e.g. Gravel 2011). Care lasts about 28 days in smallmouth, 6 in pumpkinseed (Cooke, Philipp, Wahl & Weatherhead 2006), 7–10 in New Brunswick redbreast (Gautreau & Curry 2012) and up to 29 in brown bullhead (Blumer 1985, via Animal Diversity Web).

3.5.5 Size structure and stunting

A census by number is dominated by small fish, so a density means little without its size threshold. At Cassidy Lake, Michigan there were about 1,830 yellow perch ≥ 7.6 cm per hectare but about 10 ≥ 17.8 cm, a 180-fold drop (Schneider 1973a), and in a strong perch year class autumn young outnumber older fish 20–50 times (project estimate from Michigan data). Under steady recruitment and annual survival S, the youngest J year classes hold a share 1 − S^J of all fish aged 1+, so at bullhead-like survival of 0.48 the first two year classes are 77 % of the census and at 0.73 they are 47 % (project arithmetic). Gear bends the picture further: in eastern Maine nets about 90 % of suckers and bullheads but 69 % of white perch were adults (EMAP data; project tally), Connecticut electrofishing counts perch only from 13 cm, and creel figures describe the catch rather than the stock; a net or creel sample with "30 % over 10 inches" corresponds to perhaps 10–15 % over 25 cm in a census by number (project estimate). Slow growth turns a population into small fish. Brown bullheads pass 20 cm only at about the third annulus even in a fast-growing Ottawa River population (Rubec 1975), so roughly 70–80 % of a stock surviving at about 50 % a year would be under 20 cm; white suckers reaching 30 cm by age 2–3, as at Big Bear Lake, give about 50–60 % of the stock under 30 cm, while the slow growth of a subarctic Quebec population (30 cm at about age 7) gives about 84 % (project estimates).

White perch is the species in which size structure matters most in Maine. MDIFW describes "very large populations that occasionally dominate … Usually the problem is one of too many small perch", with stunting "so extreme that a 6-year-old perch may be only 4 inches long" (10 cm), and attributes some of it to pre-1950s protective rules (Smith 2002). Cooper's 1,827 aged fish from southern Maine lakes in 1938–40 show the range: in some lakes "it was requiring from 6 to 10 years for most fish to reach a length of 6 to 8 inches"; fish from East Pond, and from Pushaw Lake in Penobscot County (Cooper's "Pushaw Pond"), reached about 17–21 cm at ages 3–5; Sabattus fish stayed at 16–17 cm through ages 5–9 and Cochnewagan fish plateaued near 25 cm from age 5 to 13. Fish lived longer where they grew slowly (mean age 7.6 in 17 slow lakes, 6.9 in 12 fast ones), and growth tracked not the density of bottom fauna but the share of fish in the diet (Cooper 1941; TL converted from SL by the project). Stunting has been tied to density (Mansueti 1961), to eutrophic waters (Hines 1981) and to "scarcity of predators" (all via Stanley & Danie 1983); a white perch population in Long Pond (Belgrade) was "tiny" until northern pike arrived in the early 1980s (newspaper column; relayed by a search summary); growth slowed as numbers rose in an invaded reservoir (Harris 2006); and removing 127,430 lb of "panfish and trashfish" from 45 Massachusetts ponds "increased markedly" panfish growth where removal was intensive (Grice 1958, abstract). Washington County lakes span the range: about 30 % of 60 Crawford Lake white perch exceeded 25 cm in 1973, Meddybemps and Long lakes yield 25–33-cm fish, whereas Southwest Pond and Pleasant River Lake hold dense, stunted stocks (MDIFW survey sheets; relayed by search summaries).

Size structure, density and biomass constrain one another, and with no survey of either lake that constraint is the main evidence on Hot Brook's white perch. The angler reports catching mostly white perch, fish "probably bigger than 6 to 8" inches (angler observations, project field notes). With normal Maine growth (20–25 cm at age 4; mean ≈ 110–150 g), 750 white perch ≥ 7.5 cm per hectare would alone weigh 82–112 kg/ha, more than the 50–90 kg/ha expected of a whole soft-water fish community; a stock that dense would have to be stunted (mean ≈ 47 g, none over 22 cm), whereas near-normal growth is consistent with about 450/ha (mean ≈ 71 g, about 10 % over 22 cm) (project estimates). The angler's sizes, the lakes' abundant bass and pickerel and the normal-sized white perch of other Washington County lakes favor the second reading; the project's census (section 4) adopted it. Hot Brook's 25-fish daily limit on white perch is probably one of the limits "imposed on seven lakes in eastern Maine … as a result of a citizen petition and not for biological reasons" (Smith 2002; project inference), and says nothing about the stock.

3.5.6 Seasonal habitat use

In a polymictic lake 4–5.5 m deep the whole column is about 22–25 °C in August, and under ice it runs from about 0–1 °C beneath the ice to 3–4 °C at the bed (project inference from Maine survey sheets and limnology; section 3.1), so depth offers neither a cold summer refuge nor much winter warmth, and what deep-lake telemetry shows must be compressed into a few meters. In unstratified Lake Opinicon, Ontario, 80–90 % of all fish biomass lay along the margins at ≤ 2.5 m (Keast & Harker 1977). Chain pickerel are the shallowest: in Milipsigate Lake, Nova Scotia (336 ha, 17 m deep), half of all depth-tag detections of tagged adults fell between 0.76 and 1.82 m, with no significant seasonal change, and smallmouth in the same lake used water about three times deeper (Sergio 2026). Pumpkinseed live in weed beds; those ≤ 75 mm SL take 76–91 % of their food from vegetation-dwelling prey (Mittelbach 1984), and small bluegill run 40–80 times the predation risk in open water (Werner & Hall 1988). Adult yellow perch school over open bottom: in shallow Lake Madison, South Dakota, telemetered perch used 1.2–4.3 m, deepest (mean 3.4 m) and farthest offshore (mean 344 m) in summer (Radabaugh 2006, thesis abstract), and in Lake Sinai they were never located in vegetation (Bauer 2006, abstract). Smallmouth in stratified Lake Opeongo held weekly mean depths of 2–4 m in summer, rising to 1.5–2.5 m at night (Suski & Ridgway 2009); in Green Lake, Maine, the only Maine telemetry found for any of these species, large bass (> 406 mm) used water deeper than 8 m in late summer more than small and medium fish, which used cover more (Cole & Moring 1997, abstract), and MDIFW places Maine bass over rocky areas and drop-offs at 1.5–4.6 m (MDIFW species page). White perch prefer level bottoms of silt, mud, sand or clay — in Sebasticook Lake, Maine they used soft muck, gravel and rock less (AuClair 1956, via Stanley & Danie 1983) — and lie at 4.0–9.0 m by day and 0.9–1.2 m at night in summer (Stanley & Danie 1983, a compilation); Maine surveys record them taken in open water at dusk, a "deep hole near the outlet" of Fifth Machias Lake as a summer spot, and schools feeding at the surface with dorsal fins out (MDIFW survey sheets; Smith 2002). White suckers in Turkey Lake, Ontario spent 84–88 % of their time within 1 m of the bottom and selected 10–16 °C, not selecting water above 18 °C in a lake whose surface reached 24.6 °C (Richter, Smokorowski & Blanchfield 2024); a 5-m polymictic lake offers no such water in August (inference). Brown bullheads loaf in weed beds by day and prowl after dark (Wisconsin DNR 2008), a rhythm that light sets: four of six captive night-active bullheads became day-active when daytime light was cut to 1 lux (Eriksson 1978, via Reebs 2002).

Autumn rearranges the lake. Smallmouth bass leave their summer ranges after mid-August and move to a few wintering sites from about a week after the autumn equinox, at 10–15 °C (Ridgway et al. 2002; Ridgway quoted by a journalist, Pyzer 2014); in Opeongo mean depth went from 4 m in late September to 14 m by mid-November, but in Milipsigate every tagged bass wintered at one of four sites shallower than 8 m, used at 2–6 m, and stayed "stationary throughout the winter until late March" (Suski & Ridgway 2009; Sergio 2026). Pumpkinseed foraging peaks in May and September (Collins & Hinch 1993); in Lake Opinicon littoral fish biomass falls in late summer as fish move offshore (Keast, Harker & Turnbull 1978), and bluegill, the nearest surrogate, regroup in the deep littoral (Hall & Werner 1977). Yellow perch are most mobile in autumn (97.6 against 45.6 m/h in summer in Lake Madison; Radabaugh 2006, thesis abstract), and white perch gather in shallow weeds in late autumn and early winter before moving to the nearest deep pool or basin by midwinter (New Jersey agency account).

Under ice the species split into active and inactive groups. Yellow perch stay active by day; in Lake Mendota they remained concentrated in the deepest water throughout the ice season, with swimming speed lowest at 0–5 °C (Hergenrader & Hasler 1966, 1967; relayed by search summaries). At Hot Brook the project places winter perch over the north basin's deepest water (4.6–5.5 m; project inference), but the angler reports few perch even through the ice (angler observations, project field notes). Chain pickerel stay active near shore: in Milipsigate, 80 % of December positions were within 30 m of shore over rocky shallows and January and February positions clustered around islands (Sergio 2026), and Maine anglers catch pickerel 2–2.5 times faster through the ice than in open water (Brokaw 2001). Smallmouth bass become nearly sessile; Maine ice anglers catch 0.46 bass per angler-day against 1.7 in open water, and "in many of Maine's bass waters, especially in Washington and Hancock counties, bass are almost never caught by winter anglers" (Jordan 2001). Pumpkinseed are lethargic but not dormant (Reeve, Rowsey & Speers-Roesch 2022); bluegill, the nearest surrogate, wintered in tall perennial weed stands of the deep littoral (Hall & Werner 1977). Brown bullheads bury in soft mud. White perch winter at 12–18 m in deep lakes (AuClair 1956; Sheri & Power 1969; both via Stanley & Danie 1983), and MDIFW says they persist in Maine lakes of at least about 20 ha and 7.6 m depth "if the deeper water is not depleted of oxygen during the winter months" (Smith 2002). Hot Brook, 5.5 and 4.0 m deep at most (MDIFW 1949), supports a principal white perch fishery, so its winter oxygen is presumably adequate (project inference); a 6.1-m Hancock County lake is "quite popular" with ice anglers for white perch (MDIFW survey sheet). White suckers in Turkey Lake wintered about 1.2 m deeper than in summer, with no thermal selection (Richter, Smokorowski & Blanchfield 2024).

Late-winter oxygen sets a ranking. In southern Michigan winterkill lakes in 1944–45, largemouth bass and bluegill died at about 0.6 ppm; yellow perch, mud pickerel, pike and pumpkinseed survived to about 0.3–0.4 ppm; and bullheads and golden shiners survived below 0.3–0.2 ppm, thousands of them living at least a week below 0.5 ppm (Cooper & Washburn 1946). White suckers died when maximum dissolved oxygen stayed below 1 mg/L for 12 days (Shroyer 2007), white perch avoid water below 35 % saturation (Meldrim et al. 1974, via Fischer, Hall & Sullivan 1989b), and smallmouth in declining-oxygen tests died at 0.5–1.6 mg/L (Burdick et al. 1954, via Doudoroff & Shumway 1970). Fish find oxygen where it enters: about 15,000 fish packed a 137-m inlet of Green Lake, Michigan, with 7.1 ppm at its head and 0.05 ppm at its mouth (Cooper & Washburn 1946), and under-ice largemouth avoided water below 2.0 mg/L (Hasler et al. 2009, abstract). In Maine, winterkill is documented in weedy ponds 1.2–1.8 m deep in snowy winters, and in Passaconway Pond only pickerel and bullhead persist through February oxygen of 0.8 ppm (MDIFW survey sheets); no winterkill is recorded at Hot Brook, an absence of record rather than a measurement. Spawning habitat is the spring counterpart: pickerel spawn at ≤ 1 m in flooded vegetation at 6–11 °C right after ice-out, perch at 7–13 °C (shallow in brown water, deep in clear), smallmouth at about 15–16 °C at 0.5–1.5 m beside a boulder or log, pumpkinseed at 0.4–0.9 m and redbreast at about 0.4 m (Table 3.5-2; section 3.6).

3.5.7 Movement: home ranges, streams, connected lakes and outlets

Within lakes the species' scales of movement differ by two to three orders of magnitude. Smallmouth in Opeongo held 200–400-ha home ranges (95 % kernel), traveled 1–9 km a day, rarely included their nest site in their summer range, reused the same range from year to year (74 % overlap) and homed from a mean 6.7 km when displaced (Ridgway et al. 2002; Ridgway & Shuter 1996); their young stayed within about 200 m of the nest, within 5 m of shore and in less than 1 m of water through September (Ridgway et al. 2002). White suckers in Turkey Lake used 14.6–18.4-ha ranges and traveled 2.1–3.2 km a day (Richter, Smokorowski & Blanchfield 2024); brown bullheads in a tidal river used 4.5 ha in summer and about 16–20 ha in other seasons (Sakaris et al. 2005); pumpkinseed ranges are about 0.2–1.1 ha (ADW, unsourced) and an introduced Polish population moved a mean 43 m between recaptures (Zięba et al. 2015, abstract); two-thirds of tagged redbreast in a Tennessee stream moved less than 100 m, a few 4–9 km (Gatz & Adams 1994, via COSEWIC 2008); home ranges of three littoral minnows, banded killifish among them, were 0.3–2.0 ha in a Minnesota lake (Valley et al. 2010; relayed by a search summary). No home range was found for chain pickerel.

The brook between Upper and Lower — MDIFW's "short (1/8 mile) non-navigable connecting stream", "rocky and hard bottomed", about 154 m long with a 0.7-m fall between the lakes' 2017 lidar water levels (MDIFW 1949; project lidar analysis; section 2) — has never been surveyed for fish. Angler observations (project field notes) are the only record: in summer sunfish, mostly redbreast with some pumpkinseed, 18–21 cm long, hold in its 0.9–1.2-m (3–4-ft) pools; pickerel and bass are in the brook, pickerel "passing through and hanging out"; bigger bass hold the deep pool at Upper's outlet, apparently "waiting for schools of small minnows"; schools of small minnows, young fallfish or dace, pass between the lakes; and in a dry August (2025) the riffles were "walk-through, almost out of the water". No study of smallmouth, pickerel, sunfish or minnows in a short brook joining two natural lakes was found anywhere, so the literature offers only analogy.

The closest analog for sunfish is an inlet creek of Big Portage Lake, Michigan (400 m long, 2.7 m wide, 0.46 m deep), where a two-way weir in March–June 1946 counted 1,786 bluegill, 654 pumpkinseed, 299 yellow and 193 black bullheads, 113 white suckers, 49 mud pickerel, 40 largemouth and 9 yellow perch moving up from the lake; the centrarchids' "migration was not for the purpose of spawning", and "many bluegills and sunfish were observed in several of the larger pools of the creek throughout the summer" (Lievense 1947). In a North Carolina river, 20 of 21 redbreast tagged in April–May and recaptured within 60 days had moved upstream, and the farthest movers went 6.1 km (Hudson & Hester 1975), and across 27 species in another southern creek larger fish tended to move upstream and smaller ones downstream (Hall 1972, abstract). Why sunfish should gather in the brook's pools is untested. Pumpkinseed prefer about 27.7 °C (Hasnain et al. 2013) and chose 27–32 °C in Lake Monona (Neill & Magnuson 1974, via Yoder 2012), above the lakes' August 22–25 °C; lake outlets run warm (natural lakes raised outlet streams by 3.4 °C in southern Quebec; Auffray et al. 2023, abstract), and sunlit slack pools may add a few degrees (project hypothesis). No study found documents sunfish congregating in warm stream pools; an outlet pool also receives lake zooplankton, 95 % of which (by biomass) was lost within 500 m below the outlets of 12 Colorado mountain lakes (Detmer, McCutchan & Lewis 2017, abstract).

Smallmouth in streams joined to lakes follow two tactics. In Millers Lake, Ontario, some bass lived in the 45-ha lake all year while others ran up the river in spring to spawn and returned before winter, most males staying faithful to river or lake for life and about half nesting within 20 m of their previous nest (Barthel et al. 2008, abstract). Once settled, stream bass are sedentary: 76 % of Snake River recaptures were in the same pool (Munther 1970, via Hafs 2007), and in Indiana only 2 of 19 bass crossed a 74-m riffle in four years (Gerking 1953). Pickerel are less known. The only telemetry beyond a lake reports "extended summer migrations beyond George Lake" in Nova Scotia, without numbers (Sauriol, Nilsen & Avery 2024, abstract); 16 % of PIT-tagged grass pickerel in Ontario drains moved more than 500 m (Zdasiuk et al. 2023; relayed by a search summary); Cooper (1941) wrote that Maine pickerel spawn "in shallow, weedy areas … or … quiet tributary streams"; and Kendall (1917) found very young Maine pickerel "find their way into the shallowest waters and mouths of brooks entering the lake" (anecdotal). Piscivores rarely follow prey into streams for the winter: in a shallow Danish lake about 40 % of roach and 55 % of white bream wintered in its streams but fewer than 2 % of pike and perch (Skov et al. 2008, abstract).

The spawning runs are better documented. White suckers run up shallow, swift, gravelly streams in early spring and spawn mostly at night (Kramer 2002), from about 10 °C elsewhere (Ontario LHD); on a Lake Michigan tributary entry of medium-sized fish, mostly white and longnose suckers, was 21 % more likely at sunset and 25 % less likely at midnight than at midday, and rose about 6 % for each 1 °C (Swanson et al. 2021); and between two Adirondack lakes a subset of mostly large suckers commuted through a short shallow channel every night in June–July, one making 29 round trips in 60 days (Marcy-Quay & Kraft 2021, abstract). White perch make "large spawning runs in the major inlet and outlet streams of some lakes" in Maine (Cooper 1941), and some stream fisheries are "migrants from nearby lakes and ponds" (Smith 2002); in February 1940 migrating white perch were found forced against the outlet screen of Great Pond by the current (Cooper 1941). Fallfish move from lakes into streams to spawn (Trial et al. 1983a), and the larvae of tributary fishes drift almost entirely at night (96 % of pooled larvae in Lake Ontario tributaries; Johnson & McKenna 2007, abstract).

Movement between connected lakes is rare per fish but steady in total. In an Adirondack chain of lakes linked by streams, where the three tagging lakes averaged 63 ha and lay about 3.5 km apart, 33,875 fish were tagged in monitoring that began in 1995, and 4,649 recaptured; 43 of them, about 0.9 % of recaptured fish, turned up in another lake — 31 white suckers, 8 brown bullheads, 2 yellow perch, 1 pumpkinseed and 1 rock bass — after 21 to 3,251 days at large (mean about 715); stocked largemouth spread about one lake every 2–5 years, stocked smallmouth were never caught in the neighboring lakes, and the authors proposed a "watershed-wide metapopulation" (Daniels et al. 2008). Across a chain of ten Wisconsin lakes the share of walleye moving rose with a lake's connections (11, 21 and 50 % for one, two and three) (Weeks 2006, abstract), and in a Minnesota lake chain larval crappie catch failed to predict year-class strength in two connected lakes, "likely due to supplemental recruitment caused by emigration from other lakes in the chain" (Parsons et al. 2004). Each spring 10–20 % of a Minnesota lake's pike ran up a 5–15-m-wide creek to spawn and 93–96 % returned (Chizinski et al. 2016). A riffle can act as "a behavioral rather than a mechanical barrier": over four years only 5 of 191 recaptured longear sunfish crossed a 74-m riffle, yet 26 of 35 transplanted longears went back across it within two weeks (Gerking 1953). Connection matters most in winter: in 18 northern Wisconsin lakes, centrarchid–Esox assemblages occurred in low-oxygen lakes only "when a stream or connecting lake offered refuge" (Tonn & Magnuson 1982, abstract).

Outflow carries fish out, and outlets gather predators. At four Maryland ponds in 1958–60, catch boxes below the spillways took 85–223 fish per acre per season at high-loss ponds against 1–6 at low-loss ones, mostly in spring and especially May; 82 % of the bass leaving one pond in July 1959 left during a single storm, and smooth spillways lost more fish than turbulent drop-board weirs (Elser 1960). A review of 57 reservoir studies found annual escapement of 0–100 %, rising with discharge and higher for small fish (Lewis et al. 2023, abstract). Predators exploit the funnel. In the Weldon Dam reservoir on the Penobscot in spring 2022, tethered Atlantic salmon smolts were eaten only by chain pickerel (43 events) and smallmouth bass (42); 23 % were taken within an hour, risk rose from 10 % to 33 % as water warmed from 5 to 15 °C, and smolts within 40 m of shore were at above-average risk (Mensinger, Casey, Mortelliti & Zydlewski 2025, abstract), and in Maine eels "gorge on juvenile alewife leaving lakes in the fall" (Maine DMR alewife page; relayed by a search summary). Shallow water is the prey's refuge and depth the predator's: bass occupied stream pools deeper than 50 cm on 72 of 75 pool-dates, fish longer than 3–4 cm avoided water shallower than 20 cm, and all six fish tethered in water under 18 cm were taken by herons or kingfishers within a day (Power 1987). In an Arkansas stream that dried into pools, smallmouth survived May–September at 67 % in the most-dried and most-fished fork against 79–84 % elsewhere (Hafs 2007), a reminder of what a dry August, like that of 2025 at the brook, can mean.

3.5.8 Angling

Maine's warmwater lakes are lightly fished by Midwestern standards. Questionnaires in 1998–99 put bass-water effort in the Penobscot region (Region F, which includes Hot Brook) at 1.8 angler-days per acre per year (4.4/ha), 22 % of it through the ice, against 4.6 statewide (Jordan 2001); white perch waters in the region drew 1.30 days per acre (3.2/ha), 20 % on ice (Smith 2002; project arithmetic); and 345,000 winter angler-days were 18 % of statewide pickerel effort in 1999 (Brokaw 2001). A Wisconsin flowage fished at about the average for north-central waters drew 182 angler-hours per hectare per year (Snow 1978). Catch per angler-day in Region F was 1.35 bass in summer and 0.14 in winter (Jordan 2001), and 1.90 white perch in open water and 1.29 through ice, of which 60 % and 68 % were kept (Smith 2002); statewide it was 0.49 pickerel in summer against 1.18 through ice, with 94 % and 79 % released (Brokaw 2001). Bass are rarely kept: 2.6 % of the open-water and 10.3 % of the ice catch statewide in 2016 (MDIFW 2019), and at Hot Brook all bass must be released. Statewide harvest was 964,889 white perch a year (Smith 2002) and 0.133 million of the 1.19 million pickerel caught (Brokaw 2001), roughly 0.6–1 pickerel kept per hectare a year, a small part of adult mortality (project arithmetic). In a Wisconsin flowage open to unlimited harvest, angling took only 5 % of yellow perch, 8 % of pumpkinseed and 2 % of brown bullhead a year against natural mortality of 48–60 %; only largemouth exploitation (27 %) exceeded natural mortality (Snow 1978). Under catch-and-release, angler catch divided by abundance implied that each smallmouth in a Wisconsin lake could be caught 3–7 times a year, and adult survival was 80–83 % (Shaw, Preul-Stimetz & Sass 2026, abstract), and tagged bass in eastern Maine have been caught by MDIFW staff "multiple times over multiple years" (Jordan 2001).

Release is not free. Wild smallmouth hooked on live minnows died at 11 % against 0 % on spinners and 4 % in unhooked controls (Clapp & Clark 1989, abstract); 8.9 % of smallmouth and 3.2 % of largemouth died after nine Maine tournaments in 1989 (Hartley & Moring 1995, abstract); a meta-analysis of 130 tournaments gave 26–28 % total mortality in the 1980s and 1990s, rising with temperature (Wilde 1998, abstract); bluegill died at 1.1 % at 16.7 °C against 25.3 % at 30 °C, season and bait confounded (Muoneke 1992, abstract); and released pike died at about 4.5 % (Tomcko 1997). Nesting male smallmouth played to exhaustion took four times as long to return to the nest (Kieffer et al. 1995, abstract). For Hot Brook no creel survey, angler diary or tournament record has been found. The lakes are "managed for a larger than average size bass fishery": all bass must be released, the daily limit on white perch is 25 fish, and from 1 October to 31 December only artificial lures are allowed (MDIFW 1949, rev. 2004; Maine fishing law books 2019–2026). Effort is estimated at about 12 angler-hours per hectare per year on Upper (range 5–25) and 4 on Lower (1–10), with about a fifth of Upper's and a quarter to a third of Lower's on ice (project estimates from Region F rates). About 70 % of the angler's logged catches are smallmouth (Upper 8 of 11, Lower 16 of 22), while the angler also reports catching mostly white perch (angler observations, project field notes); since eastern Maine nets find white perch the most numerous adults, catches reflect what anglers target and what bites — per fish, white perch are perhaps a tenth as catchable as bass (project estimate from Region F rates) — not what the lakes hold.

3.6 Early life and recruitment

No egg, larva or young-of-year fish has been counted, measured or aged at Upper or Lower Hot Brook Lake, and the agency surveys of the lakes record none. This section therefore draws on other waters: where possible soft-water, colored or small lakes in Maine, New Brunswick, Nova Scotia and Ontario, otherwise the Great Lakes region and the laboratory. The lakes' eleven resident species fall into three reproductive groups, and the group largely decides where early losses fall. Chain pickerel, yellow perch and white sucker spawn without care in cold water soon after ice-out, leaving adhesive or scattered eggs, or gelatinous ribbons, on vegetation, wood or gravel for one to three weeks. White perch, the seasonal sea-run alewife and banded killifish also give no care but spawn later in warmer water; fallfish and blacknose dace spawn on stream gravel, the fallfish on mounds the male builds. Smallmouth bass, pumpkinseed and redbreast sunfish (males) and brown bullhead (usually both parents) guard nests. The spawning order after ice-out runs from chain pickerel (about 6–11 °C; Ontario Freshwater Fishes Life History Database) and yellow perch (7–13 °C; USFWS habitat suitability index model for yellow perch), through white sucker (from about 10 °C; Scott & Crossman 1973) and smallmouth (nests from 12.8 °C, eggs at 15.6–18.9 °C, mid-May to mid-June in Maine; Jordan 2001), to white perch (about 15 °C; AuClair 1958; Smith 2002), pumpkinseed (17–26 °C; Ontario Freshwater Fishes Life History Database), redbreast (about 20 °C, late June to early July in New Brunswick; Gautreau & Curry 2006, via COSEWIC 2008) and banded killifish (19–23 °C in Newfoundland; Chippett 2004, via COSEWIC 2014). Table 3.6-1 summarizes the egg and yolk-sac stage of each species.

Table 3.6-1. Spawning, egg and yolk-sac stage of the Hot Brook fishes (field and laboratory values from other waters).

3.6.1 Eggs: incubation and three meanings of "egg survival"

Incubation shortens steeply with temperature, so the cold spawners carry their eggs longest. Eurasian perch need about 97 degree-days above 4.9 °C to reach 50 % hatch (Guma'a 1978, abstract); yellow perch eggs near the surface of a Pennsylvania lake hatched in 9 days at a mean 13.3 °C, while deeper eggs at 7.7–11 °C took 19–35 days (Huff et al. 2004, abstract). The early spawners' eggs therefore sit for one to three weeks through the cold fronts, wind and falling water of late April and May, while centrarchid and white perch eggs are typically exposed for two to six days and their risk lies mainly in the nest and yolk-sac stages (project synthesis).

Three different quantities are reported as "egg survival", and they differ by one to two orders of magnitude. Fertilization and early viability are high: perch ribbons are more than 90 % viable in the field (95.3 % at Lochs Kinord and Davan, Scotland, Treasurer 1983, abstract; a mean of 99 % to the eye-pigment stage in Lake Zürich, Zeh, Ritter & Ribi 1989, abstract; "generally over 95 %" at Oneida Lake, Clady, via Dahlberg 1979), and white sucker eggs are more than 90 % fertilized (Stewart 1926). Hatch in the laboratory is lower and temperature-dependent: white perch hatched at about 80, 60 and 20 % at 13, 17 and 21 °C (Margulies 1989), and hatchery yellow perch ribbons yielded 19.9–49.6 % viable larvae (Linkenheld 2019); for perch the laboratory understates the field (91.6 % viable in situ against 84.1 % for the same eggs in the laboratory; Delos Reyes, Arzbach & Braum 1992, abstract). Field survival of unguarded eggs on a lake bed can be far lower: walleye eggs in a Minnesota lake reached the eyed stage at 25 % on gravel–rubble but 0.6 % on muck (Johnson 1961, abstract), and rainbow smelt eggs on Maine lakeshores hatched at a mean of 1.1 % (Rupp 1965, via Dahlberg 1979). Dahlberg (1979) concluded that hatching success "is often low in freshwater species which do not guard the demersal eggs". The perch ribbon is the exception, credited to its envelope (Clady, via Dahlberg 1979); eel, white sucker, brown bullhead, yellow perch and sticklebacks all refused ribbons in feeding trials (Newsome & Tompkins 1985, abstract). For white perch, which one angler reports as the commonest catch in the Hot Brook lakes (angler observations, project field notes), no field measurement of egg survival was found for any water.

Substrate matters most for the unguarded spawners. Eyed yellow perch eggs in a hatchery trial hatched at 98.6 % on artificial vegetation against 46.2 % on a bare bottom (Ward & Barnes 2020), and dead embryos were commoner in Eurasian perch strands lying on the bottom than on vegetation (Smith, Douglas & Jurajda 2001, abstract). Because perch and pickerel spawn soon after ice-out, their substrate is last year's dead stems, wood and overwintering plants; in a Czech lake Eurasian perch laid mainly on dead pondweed and reed while it lasted, and 96 sunken trees took two thirds of the strands (Čech et al. 2009, abstract; Čech et al. 2012). After 73 % of the large wood was cut from the shore of Little Rock Lake, Wisconsin, yellow perch fell from 141 to about 5 per hectare, though bass predation and the loss of spawning substrate cannot be separated there (Sass et al. 2006). For pike the evidence conflicts: egg survival on vegetation in Minnesota was 60–95 % (Franklin & Smith 1963, via Dahlberg 1979), but hatching in an English gravel pit was 11 % on sand and silt against 2.5 % on plants (Wright & Shoesmith 1988, abstract). White sucker eggs gather in current (710/m² in a riffle against 0.5/m² in quiet water; Corbett & Powles 1986, abstract), so the riffles of the brook between the lakes are the likely sucker spawning ground (project inference).

The physical hazards are cold snaps, wind, silt, falling water and fungus. Sudden drops of 2–3 °C kill white perch eggs and drops of 4–5 °C are lethal (AuClair 1960 and Hardy 1978, via Fischer, Hall & Sullivan 1989b); for Maine, AuClair (1958) wrote that a sudden fall of about 2–3 °C (4–5 °F) can kill all the eggs deposited, and MDIFW attributes white perch year-class failures only to weather at spawning time (Smith 2002). Perch embryos tolerated a 16-hour cold shock to 10 °C better than a warm spell to 20 °C (49.6 against 19.9 % viable; Linkenheld 2019), whereas early pike embryo mortality "approached 100 %" with sudden drops below 10 °C (Hassler 1970, abstract). One windy day piled almost 1 % of Oneida Lake's estimated perch egg potential into a single windrow (Clady & Hutchinson 1975, abstract), and a wind-mortality term on the embryos explained 52–61 % of the year-to-year variation in perch egg masses in four of six demes at Lochaber Lake, Nova Scotia (Aalto & Newsome 1993, abstract). A silt layer over 2 mm deep killed every white perch egg and one under 0.45 mm had no effect (Morgan, Rasin & Noe 1983, abstract). Pike survival from egg to age 0 was 0.037 % with natural water levels against 0.399 % with the level held (Massé et al. 1993, abstract). Saprolegnia spreads from dead to live eggs within about three days even at 4–7 °C (Ali et al. 2014). Brown bullhead eggs die within about a day in still water (Breder 1935; Armstrong 1962), so they depend on the parents' fanning (project inference). Ultraviolet light, which killed every exposed perch egg in a clear Pennsylvania lake (Williamson et al. 1997, abstract), is unlikely to matter in Hot Brook's colored water (project inference). Banded killifish eggs need warmth: none hatched at 10 °C, at most 10 % at 16 °C and more than 74 % at 22–28 °C (Penney, Litt & Purchase 2019, via a thesis). White sucker egg-to-larva survival is unsettled at "as little as 3 percent" (Scott & Crossman 1973, via Dahlberg 1979) or 0.3 % (attributed to Geen et al. 1966 by a search summary; Geen's abstract gives no figure).

3.6.2 Nests, guarding and nest success

Smallmouth nest success, the share of nests producing swim-up fry, is moderate and variable: 44–96 % in lakes with a median near 75 % across 26 studies (Steinhart 2004), a mean of 50.6 ± 4.7 % across 30 values in another compilation (Cooke et al. 2003), and in Jones Bay of Lake Opeongo, Ontario, 49.5 % of 1,187 nests over 20 years produced fry to the "green fry" stage, an endpoint the source does not equate with swim-up (Suski & Ridgway 2007). The one Maine study, at South Branch Lake (Penobscot County) in 1971–72, found nesting success of 67 % and 77 % and an average of 3,943 fry rising from each nest; a fall in water level was judged the main cause of the poorer 1971 season, egg mortality was highest under males shorter than 400 mm with large egg deposits, and fanning lowered sac-fry but not egg mortality (Neves 1975, abstract). Nests reach at least 71 per kilometer of suitable shore at Big Lake, Maine (Watson 1955, via Forbes 1981), and 13 per km of shore (1.43/ha) at Sanford Lake, a tannin-stained, soft-water (9 ppm alkalinity), wood-rich Wisconsin lake that is the closest physical analog found (Short 2001). Not every adult breeds: females deposited only 15–34 % of their potential eggs at Katherine Lake, Michigan (Clady 1975), and only 12–47 % of mature Opeongo males spawned in a given year (Post 1982, via Chu 2001).

Losses continue inside successful nests: about 28 % of eggs became black fry at Waugoshance Point, Lake Michigan (7,437 eggs per nest in two nests and 2,054 fry per nest in three; Latta 1957), deposited egg to postlarva was 26–33 % at Katherine Lake (Clady 1975), and on-nest survival at Sanford Lake averaged 22.7 % (Short 2001). Daily survival within guarded broods is about 0.90 for embryos and 0.92 for larvae (Steinhart et al. 2008), and at Opeongo only 34 % (1991) and 52 % (1992) of nesting males still had broods at the juvenile stage (Mackereth, Noakes & Ridgway 1999). Cold drives desertion: when the water at Waugoshance fell to 10 °C on 16 May 1955, "all of the nests were deserted" by the next day and the eggs were "taken almost immediately by some predator" (Latta 1957). Storms destroyed nests at 0.015 per day at Opeongo and 0.065 per day in Lake Erie (Steinhart 2004). "It is generally agreed that unguarded nests will fail" (Forbes 1981): in bluegill colonies, median predation loss was 68 % from unguarded and 14 % from guarded nests (Bain & Helfrich 1983, abstract), and removing the male before about 10 days after swim-up lost the whole brood (Ridgway 1988, via Bremigan et al. 2008); named predators of unguarded nests include carp, suckers, white perch and crayfish (Forbes 1981). In four northern Wisconsin lakes, though, failures came from fungus with the male still present (Saunders 2006).

Nest temperature is the best-documented control near Hot Brook. At Spednic Lake on the Maine–New Brunswick border, Dudley & Trial (2014) applied the rules of Shuter et al. (1980): spawning starts once daily water exceeds 15 °C (modeled median 28 May), and the proportion of eggs and fry dying is 1 if the minimum temperature in the following 15 days falls below 10 °C and 3.0 − 0.2·T_min between 10 and 15 °C. Modeled early mortality exceeded 10 % in 17 of 39 years (1970–2008), reaching 56 %. Males guarded for 28.4 ± 2.2 days at Lake Opinicon, Ontario (Cooke et al. 2006); at Opeongo average-length males were only 2.4 % lighter after 19 days of guarding (different fish sampled at the start and end; not significant), and 64 % had prey in their stomachs (Steinhart et al. 2005).

The sunfish and the bullhead are less studied. At Deep Lake, Michigan (6 ha), pumpkinseed built 97–188 nests a year and averaged 6,012 fry per nest, with dead or fungused eggs and fry in "almost every nest" (Carbine 1948). Bluegill, the best-studied congener, show what threatens colonial nests: egg viability on the nest fell from 86.5 % to 57.4 % by day 4 (Beard 1982); Saprolegnia infected 38 % of eggs in solitary nests against 19 % in colonies (Côté & Gross 1993, via Neuswanger et al. 2015); at Lake Opinicon 94 % of water-column brood predation was by bluegill themselves, snails and fishes (mostly bullheads) took 11 % and 7 % from the substrate, and edge nests lost at least three times more than interior ones (Gross & MacMillan 1981, via Neuswanger et al. 2015); crayfish at 1.4/m² destroyed every nest in small colonies within four weeks in Michigan ponds (Dorn & Mittelbach 2004, via Neuswanger et al. 2015). Crayfish are "generally rare in Maine" (Cooper 1941) and an angler reports them uncommon at Hot Brook (angler observations, project field notes), so crayfish nest predation is probably weaker there (project inference). Redbreast sunfish have no lake data; in a Virginia stream high flow destroyed all May nests and 33 % of nests overall produced swim-up fry (Lukas & Orth 1993, abstract). Brown bullhead broods were attended by both parents in 56.2 % of cases and by the male alone in 39.3 % (Blumer 1985, 1986b, via Animal Diversity Web); attendance raised survival mainly against predation (Blumer 1982, thesis abstract), and broods whose parents were both removed "never reached the larval stage" (Blumer 1986a, abstract).

3.6.3 Yolk-sac larvae, first feeding and larval prey

Between hatching and the first meal, unguarded species lose roughly a quarter to nine-tenths of their larvae (project synthesis): only 11.5–73.2 % of hatched Eurasian perch reached the pelagic stock at Lochs Kinord and Davan (Treasurer 1983, abstract), and pike yolk-sac survival was 57.2 % over 8 days in an Oneida Lake marsh (Forney 1968, via Dahlberg 1979). The causes named are littoral predation, cold and turbulence, and cold is the best documented (project synthesis). In May 1976 few white perch larvae longer than 5 mm were caught in the Hudson River despite large egg catches, a loss attributed to "the temperature drop to 12 °C", and the year class came from a second spawning (Texas Instruments 1979). At Oneida Lake in 1969–75, egg-to-8-mm survival of yellow perch was 1.6–18.4 % with "80+ percent base mortality" every year, and air temperature in the three weeks before 8 mm (positively) and wind in the preceding four weeks (negatively) explained 87 % of the variation (Clady 1976, abstract).

First foods are small (Table 3.6-2). In Lake Opinicon young yellow perch, pumpkinseed, bluegill and three other species began feeding at 4.5–6.0 mm on nauplii and cyclopoids of 0.1–0.3 mm and took cladocerans from 8–10 mm (Keast 1980, abstract). Rotifers matter only briefly: they gave yellow perch larvae little or no growth (Graeb et al. 2004, abstract), white perch larvae did not select them (Limburg et al. 1997, abstract), and by the project's arithmetic a 6-mm larva growing 0.4 mm/d needs about 4,600 rotifers, or 1,700 nauplii, or 140 Bosmina a day, so rotifers cannot carry a larva much past 6–7 mm (project estimate). The resulting ladder is consistent across species: rotifers, nauplii and small cyclopoids below about 8 mm; Bosmina, small cladocerans and adult copepods at 8–12 mm; larger cladocerans beyond; and bed invertebrates from about 20 mm in sunfish and pickerel and 40–50 mm in the perches (project synthesis).

Table 3.6-2. First foods and diet shifts of young fish.

3.6.4 Larval densities in lakes

Field larval densities are standing stocks from single-date tows, lower than the cumulative number produced over a hatching season. With that caveat, typical peaks are of the order of 0.1–5 larvae/m³ per species, with exceptional local peaks of about 12–42/m³, and all species together probably sum to no more than 10–40/m² at the seasonal peak (project synthesis; Table 3.6-3). Larvae are patchy: Lepomis larvae at Lake Mendota and Lake Opinicon were much denser in shallow open water near the colonies than far offshore, and at the deepest Opinicon site density was 8 % of the inshore mean (Post, Rudstam & Schael 1995; Garvey, Herra & Leggett 2002; both via Neuswanger et al. 2015), and pumpkinseed larvae at Ashby Lake were seven times denser in sheltered littoral bays (Sobchak, Colborne & Robinson 2026). Yellow perch larvae move offshore soon after hatching, "probably a mechanism to escape intense predation in the littoral zone" (Whiteside, Swindoll & Doolittle 1985, abstract). No larval density was found for any Maine lake, and for white perch in a lake only Oneida's long larval series exists, in a paywalled paper (VanDeValk et al. 2016).

Table 3.6-3. Larval densities measured in lakes and analogous waters.

3.6.5 Larval mortality and its causes

Daily instantaneous mortality (Z) of larvae in lakes spans more than an order of magnitude (Table 3.6-4). Among yellow perch, the lowest rates come from sparse pelagic larvae with ample food (Oneida, about 0.04/d; the basin of West Blue Lake, 0.017/d), rates of 0.14–0.5/d from crowded or food-short larvae, and rates above 1/d from larvae overlapping an abundant planktivore. Across lakes with fish, larvae of 5–20 mm die at about 0.05–0.3/d, against 0.01–0.05/d where fish predators are excluded (project synthesis). Survival to metamorphosis is predicted to average about 5.3 % in freshwater species against 0.12 % in marine ones (Houde 1994, abstract).

Table 3.6-4. Instantaneous daily mortality of larvae and early juveniles.

Fish predation appears to explain most of the gap between lake and predator-free rates (project synthesis). Walleye larval mortality in lakes was "an order of magnitude higher" than in enclosures and ponds without fish, and in one pond series it rose to 0.134/d in the year piscine predators were present (Johnston 1995). Yellow perch larvae died at 1.58/d in a Lake Ontario embayment pond with abundant adult alewives against 0.22–0.28/d without them, and in 1984, when the alewives arrived three weeks after the hatching peak, they took none (Mason & Brandt 1996, abstract). At Lochs Kinord and Davan, perch larvae were in 59–63 % of adult perch diets and cannibalism "would have been responsible for a large proportion of the mortality of larvae" (Treasurer 1997). Young largemouth ate 58–93 % of littoral bluegill fry at Ridge Lake, Illinois (Santucci & Wahl 2003, via Neuswanger et al. 2015), and Oneida's monitors cite "direct predation on percid fry by white perch" (VanDeValk et al. 2023). In laboratory trials, yearling bluegill killed nearly every white perch larva under 6 mm SL but 18 % at 14 mm, and a hundredfold increase in Daphnia cut larval mortality by 75–90 % (Margulies 1990, abstract). For Lower Hot Brook's alewife run the one Maine record is direct: at Lake George, Maine, adult sea-run alewives ate larval yellow perch, 35 % of food items in May 1992, and 9 of 17 adults held 101 fish (mainly perch larvae) in May 1991 (Kircheis et al. 2002); adults in Downeast lakes, by contrast, ate mostly zooplankton, with fish under 0.15 % of the diet by an importance index (Willis 2006). Whether the Hot Brook run overlaps the perch larvae is unknown.

Invertebrate predators threaten the smallest larvae but have not been shown to dominate any lake. In Lake Michigan 98 % of cyclopoid copepods found attached to larvae were on alewife larvae of mostly 3–8 mm, and none on yellow perch, which were "apparently immune" (Hartig, Jude & Evans 1982, abstract), although Diacyclops thomasi did attack newly hatched perch where the larvae reached 41.9/m³ (Hartig & Jude 1984, abstract). Hydra canadensis at up to 30,000/m² on Myriophyllum killed up to 20 % of a colony's bluegill larvae within 2 m of the nests at Lake Opinicon (Elliott, Elliott & Leggett 1997, abstract). For walleye, cyclopoids were judged "a minor source" of loss (Johnston 1995). No record of Chaoborus or Leptodora eating fish larvae was found.

Starvation is fast when it happens, but no direct field estimate was found for any freshwater larva, and the evidence for Hjort's "critical period" at first feeding is "mixed and equivocal" (Houde 2008). Yellow perch starved from hatch reached 50 % mortality 2.7–6.3 days after hatching, at an inferred 14–16 °C, with maternal lines differing twofold in resistance (Heyer 2000); unfed perch survived up to 15 days at 19.8 °C and 65 days at about 6 °C (Hokanson & Kleiner 1974, via Johnston 1995), and 8–24-mm walleye passed the point of no return after 6–8 days at 15–25 °C (Jonas & Wahl 1998, abstract). Partial feeding is also lethal: at 17–21 °C, white perch first feeders at 50 rotifers/L grew almost nothing and survived 80–90 % less over eight days than at 800/L, and a four-day delay in first feeding cost 60–80 % of survival (Margulies 1989). Yet 65–79 % of 5–6-mm bluegill larvae in Alabama ponds had empty stomachs early in the season (Partridge & DeVries 1999) while bluegill larval survival in Illinois mesocosms and Lake Shelbyville was "uniformly high" whatever the zooplankton (Welker, Pierce & Wahl 1994, abstract), and Johnston (1995) judged starvation "probably not a major source" of walleye loss, acting mainly by prolonging vulnerability to predators. July plankton in comparable north-eastern and upper-Midwest lakes (medians of about 450 rotifers, 65 nauplii and 37 small cladocerans per liter in EPA National Lakes Assessment data) exceeds the first-feeding thresholds found for other species and lies within the 50–800 rotifers/L bracket left open for white perch (project analysis), so in Hot Brook starvation is more likely episodic and patchy, in the days after yolk exhaustion, than a season-long cause (project inference).

Variability within and between cohorts is large. Yellow perch in Canadian Boreal Shield lakes had the widest scatter in gut contents at length of 14 larval populations (residual SD of log₁₀ gut carbon 0.71; Pepin et al. 2015), and selection usually favors fast growers, larger size being favored in 77 % of selection differentials across 40 studies (Perez & Munch 2010, abstract). Hatch date matters, but not always the same way: at Lake Opinicon the earliest third of bluegill fry rose 231 % in representation among yearlings in 1993 (Cargnelli & Gross 1996, abstract), whereas in 1998 a cooling from 70 to 64 °F (21 to 18 °C) right after the early larval peak was followed by poor survival of early cohorts (Garvey, Herra & Leggett 2002, via Neuswanger et al. 2015). Between years, autumn white perch abundance in north-eastern Lake Ontario varied about 200-fold over 1978–97 (O'Gorman & Burnett 2001, abstract). Failures are species by species: Lake Jesse, Nova Scotia, an 18-ha soft-water lake of 2.4 m mean depth, held no young white perch at all in 1934 (Smith 1939), Loch Davan's perch year classes were twice eliminated in their first summer (Treasurer 1989), and young perch were present in Crystal Lake, Wisconsin, only in 1981–82, 1986–87 and 1990–91 (Sanderson et al. 1999). Combining the stages, survival from egg to the first autumn is a fraction of a percent to a few percent where predators are present (Table 3.6-5).

Table 3.6-5. Survival from egg or fry to the first autumn.

3.6.6 Larval and juvenile energetics and growth

Young fish are not small adults energetically. Young-of-year yellow perch had the adult slope of active metabolism on mass but at 4.4 times standard metabolism (adults 1–2 times), and ate more than adult allometry predicts (Post 1990, abstract); early-life mass-specific metabolic rates were independent or nearly independent of mass (slopes −0.45 to +0.14; Post & Lee 1996, abstract), and pike larvae's mass-specific routine oxygen uptake is independent of mass below about 10 mg (Wieser, Laich & Medgyesy 1992, abstract). Young Oneida perch eating Daphnia pulex took in 23 % of their body energy (time basis not stated, presumably per day), assimilated about 68 % and converted about 27 % to growth (Mills & Forney 1981, abstract). Larval energy density is low: 2,300 J/g wet for age-0 bluegill, whose dry matter is about 10 % of wet mass below 6 mm (Breck 1997, citing Craig 1977), and about 3.5 kJ/g wet for pike larvae at first feeding (Trabelsi-Zouari 2011; project conversion), against 5,724–6,331 J/g in laboratory-fed young white perch of 3–9 g (Hanks & Secor 2011). Breck (1993, 1997) found that young bluegill "would not grow fast enough" on the Fish Bioenergetics consumption curve fitted to adults until its intercept was raised by 50 %.

Table 3.6-6. Growth of larvae and young-of-year in length.

Food and crowding shape first-summer growth as well as temperature (Table 3.6-6). Bluegill growth in Michigan ponds fell from about 0.6 to 0.2 mm/d once crustacean zooplankton (rotifers excluded) fell below about 50/L, and in simulation a tenfold increase in fry density cut final length by 47 % (Breck 1997). Large Daphnia pulex at Oneida withstood about 10 kg/ha of age-0 perch but collapsed above 20–40 kg/ha (Mills & Forney 1983, abstract); in 1987, when D. pulex vanished, young white and yellow perch switched to bed invertebrates and grew more slowly (Prout, Mills & Forney 1990, abstract). Over 54 years at Oneida, young yellow perch at 20,000–39,000/ha were 37–41 mm long on 1 August against 51–65 mm at densities below 1,000/ha (Rudstam & Jackson 2022). Warmth helps too: the mean autumn length of young white perch in north-eastern Lake Ontario tracked degree-days above 15 °C (r = 0.69; O'Gorman & Burnett 2001, abstract), and Hudson young were larger in warm summers and smaller after dense larval years (Gallagher 2016).

3.6.7 The first summer: habitat, refuges, size and numbers

Each species leaves the larval stage for a different nursery. Larval Lepomis and other species spent three to seven weeks in open water in Lake Mendota (Post, Rudstam & Schael 1995, abstract); bluegill return to the littoral at about 12.5 mm SL and the small ones stay in vegetation, because open water is 40–80 times riskier for them although more profitable for every size class (Werner & Hall 1988; Hall & Werner 1977; both abstracts), at a cost of 27 % less growth in a divided-pond experiment (Werner et al. 1983, abstract). Yellow perch larvae stay offshore, then commute inshore by day as they grow, and are wholly nearshore by about 30 mm TL (Post & McQueen 1988, abstract). In the Patuxent River estuary, young white perch settle on the shallow shore (≤ 2 m) at 20–25 mm, about 45 days after hatching (Kraus & Secor 2004); in Maine, young of 25–76 mm were seined "by the thousand" along sandy beaches in the evening (AuClair 1958). Young pickerel find "the shallowest waters and mouths of brooks entering the lake" (Kendall 1917, Maine), and 95.8 % of grass pickerel under 7 in (178 mm) in a Wisconsin lake came from one 6-ha vegetated bay and slough (Kleinert & Mraz 1966). Banded killifish in Maine "rarely stray into water much over a foot in depth" (Everhart 1958).

Young smallmouth stay near the nest. After two to three weeks with the male (Scott et al. 1997 and Friesen & Ridgway 2000, via Ridgway et al. 2002) the fry disperse at about 28 mm (Opeongo) and live singly or in small groups, in shallow water among stones or sticks and avoiding weed beds (Hubbs & Bailey 1938, via Forbes 1981). DNA-fingerprinted young at Lake Opeongo had moved a mean of 87.6 m from their nests by September, almost all less than 200 m (Ridgway et al. 2002). Young-of-year occurred only over sand and silted rock in Little Moose Lake, New York, while adults used wood and cobble (Brown, Josephson & Krueger 2000, abstract), and in Wisconsin cobble gave protection "without attracting predators" (Brown & Bozek 2010, abstract). At New Brunswick's northern range limit, age-0 fish sheltered in gaps in the substrate below about 10 °C and were mostly in water under 3 m by autumn (Curry et al. 2005, via a secondary source). Predation on young bass falls steeply with size; one model used 0.2·e^(−0.04·L) per day (L in mm), about 0.13/d at 10 mm and 0.027/d at 50 mm (DeAngelis et al. 1993, from an unpublished thesis by Houpt 1991). In Maine, MDIFW cites a "lack of significant predators on juvenile bass" (Jordan 2001), and Cooper's (1941) 36 smallmouth stomachs with food held no bass.

By autumn most young of these species are 25–130 mm long (Table 3.6-7). Length grows roughly linearly through early summer and plateaus by early September, and spawning date is the strongest influence on autumn size (Keast & Eadie 1984, abstract, nine species in Lake Opinicon). No first-summer lengths of white perch were found for Maine, New Hampshire, Lake Champlain or Quebec. Late-summer densities range from tens to thousands per hectare (Table 3.6-8). The long Oneida record gives about 950 yellow perch per hectare on 15 October and a median of about 140 white perch per hectare in August–September over 1961–2022 (if the source table's unstated unit is per acre), reaching about 6,700/ha in the best year; the white perch values of 2,900–7,200/ha come from western Lake Erie and the Hudson estuary, much larger waters, and the project notes judge about 100–1,000/ha, with strong years of a few thousand, the defensible range for soft-water, oligo-mesotrophic Hot Brook (project inference).

Table 3.6-7. Length of young-of-year at the end of their first growing season.

Table 3.6-8. Densities of young-of-year in late summer and autumn.

3.6.8 The first winter

In long northern winters young warmwater and coolwater fish feed little and live on stored energy. Because the ratio of stored energy to basal metabolism rises with body size, small fish die first, and the first-summer growth needed to survive increases northward; Shuter and colleagues argued that this alone can explain the northern range limits of smallmouth bass, yellow perch and Eurasian perch (Shuter et al. 1980; Shuter & Post 1990; both abstracts). At Spednic Lake, the regional analog with a first-year bass analysis, the winter (days below 10 °C) averaged 208 ± 4 days; at that length the Shuter thresholds predict that all young smallmouth under 48 mm die and all over 92 mm survive, so the measured autumn lengths of 71–76 mm imply a 36–49 % first-winter loss (Dudley & Trial 2014; the loss is project arithmetic from their thresholds). MDIFW states that young bass under about 56 mm (2.2 in) do not survive their first winter (MDIFW 2021), a period of 200-plus days below 50 °F (10 °C) without feeding (Jordan 2001), and Dudley & Trial (2014) record year-class failures after the cold, wet summers of 1986 and 1996. Under ice in northern New Brunswick, young smallmouth under 50 mm died and survivors lost 22–54 % of their ash-free dry weight (Curry et al. 2005, abstract). Table 3.6-9 gathers the size thresholds.

Table 3.6-9. Size dependence of first-winter survival.

Yellow perch give the clearest evidence for starvation. In simulated winters 1 % of fed but 46 % of starved age-0 perch died, small fish lost proportionally more mass, size-selective loss was confirmed in enclosures and five natural cohorts, and winter length drove both total and size-selective mortality; simulations suggested that winter starvation can cause substantial year-class variability independent of adult stock (Post & Evans 1989, abstract). At Oneida the winter mortality index fell as October length rose (R² = 0.382, n = 38; Irwin et al. 2009). White perch are the more vulnerable in very cold water: after 150 days at 2.5 °C, 71.2 % of white perch died against 0.8 % of yellow perch (at 4.0 °C the order reversed, 11.1 % against 17.7 %); white perch "remained active throughout the winter" while yellow perch rested on the bottom and used 25.8 % less oxygen (at 4 °C), and similar-sized white perch died at 3.3 times the yellow perch rate in Great Lakes-type winters (Johnson & Evans 1991, abstract). At 2.5 °C osmoregulatory failure adds to starvation (Johnson & Evans 1996, abstract). In Oneida Lake, age-0 white perch winter mortality rose with total predator biomass and with autumn white perch abundance and also correlated with a starvation model, while predation dominated for yellow perch (Fitzgerald et al. 2006, abstract).

Size-selective winter loss is not universal, and in milder winters predators rather than starvation appear to do the selecting. It appeared in only 5 of 12 bluegill and largemouth studies and not in a fathead minnow population (Toneys & Coble 1979), and not in central European Eurasian perch (Radke & Eckmann 1999, via Eckmann 2004). In Ohio, rations from none to 1.5 times maintenance did not change the winter survival of young largemouth, and small fish died at high rates only with predators present (Garvey, Wright & Stein 1998), whereas in a northern Michigan lake the size-dependent loss was "likely the result of starvation" (Post, Kitchell & Hodgson 1998, abstract). Predators raised the overwinter loss of 28-mm age-0 bluegill in Michigan ponds from 10 % to 39 %, and to 55 % with walleye alone (Schneider & Breck 1997, via Neuswanger et al. 2015). No first-winter data were found for chain pickerel, white sucker, brown bullhead, fallfish, blacknose dace or banded killifish. The project notes judge that 30–70 % of a northern cohort typically survives its first winter where predators are present, swinging toward none or all with autumn size relative to the threshold and with winter length (project synthesis).

3.6.9 Pickerel and pike: first-year survival and larval energetics

No first-year survival, young-of-year density or age-0 mortality was found for chain pickerel, so the esocid values come from northern pike and grass pickerel. In an Oneida Lake marsh pike eggs survived 18 % over 13 days, yolk-sac larvae 57.2 % over 8 days and post-larvae 29 % over 22 days, about 3 % from egg to day 43 (Forney 1968, via Dahlberg 1979); egg-to-fingerling survival in Wisconsin marshes was 0.15–2.69 % (Fago 1977). In shallow Lake Hestholm, Denmark, 0+ pike survived 17.5 % from May to September and about 46 % from December to March (Falck-Rasmussen 2005). Weed cover matters: a weedy English gravel pit gave about 1.8 times the survival and 3.5 times the age-0 production per hectare of a plant-poor one (Wright 1990, abstract; project reading). At Windermere, pike survival from egg to age 1 was estimated at 0.0001–0.0007 in 50 of 53 years (mean 0.00028; Vindenes et al. 2016). Cannibalism starts early: the smallest cannibal at Houghton Lake, Michigan, was 21 mm, and 13.3 % of 354 pike of 21 mm or more had eaten pike (Hunt & Carbine 1951, abstract); in ponds, cannibals were 7.8 % of ~100-mm juveniles at low density but 41.3 % at high density (Bry et al. 1992, abstract). Of eight pickerel of 108–162 mm caught together (place not stated), six held fish, and four of the prey were young pickerel (Kendall 1917). When falling water cut off a slough nursery, grass pickerel year classes were three to four times smaller (Kleinert & Mraz 1966).

Pike larvae grow fast in warm water: with live food in excess, from about 0.45 mm/d at 12 °C to 0.8–1.2 mm/d at 24 °C (project calculation), with cannibalism appearing at 18 °C and reaching 26 % at 24 °C (Górny 1992); larval growth peaks at 26 °C, but net biomass gain at 21 °C (Hokanson, McCormick & Jones 1973, abstract). Routine oxygen uptake of unfed larvae rose with a Q10 of about 2.4–2.6 between 5 and 25 °C (Woynárovich 1960; project calculation). Chain pickerel hatch smaller (4.2–7.0 mm) and first feed at about 10 mm, against a 6–8-mm hatch and first feeding at 12–15 mm in pike (Ontario Freshwater Fishes Life History Database; Underhill 1949, via secondary sources; Harvey 2009 for pike). No larval bioenergetics model was found for any esocid, and the juvenile models overestimated consumption by 39–52 % in Ohio reservoirs (Wahl & Stein 1991, abstract) and by 113 % at 10 °C and 328 % at 7.5 °C in tiger muskellunge (Chipps, Einfalt & Wahl 2000, abstract).

3.6.10 Stock, recruitment and compensation

For perch, sunfish and bass the number of eggs predicts recruits poorly, because survival of the young is density-dependent. Perca, Lepomis and Micropterus are absent from the 49 species analyzed for maximum reproductive rate (Froese & Luna 2004, from Myers, Bowen & Barrowman 1999), and no stock–recruitment parameters were found for any white perch population. The Oneida yellow perch record shows compensation moving between stages. In 1959–68 age-0 mortality was depensatory, weak year classes suffering higher August–October mortality, consistent with walleye predation (Forney 1971, abstract), which Irwin et al. (2009) attribute to walleye consumption saturating at high perch density. Across the long-term record, larval mortality was not density-dependent (R² = 0.024) but open-water growth was (R² = 0.507), and winter mortality fell with October length, so that compensation now acts "through the first winter and second spring" (Irwin et al. 2009). An individual-based model of the lake agreed: halving or raising egg mortality changed first feeders 4.4-fold but age-2 recruits by only about 8 % (205, 210 and 221 per hectare), and the share mature at age 4 rose from 24 % (low egg mortality) to 54 % (high), through lower perch density (Rose et al. 1999, via Rose et al. 2001). Oneida's white perch differ: dense larval year classes grew more slowly and died faster, but "mortality did not compensate for the higher initial densities", and recruitment was best explained by larval density together with predator biomass (VanDeValk et al. 2016, abstract).

The centrarchids compensate strongly after the egg stage. Poisoning bluegill nests with copper sulfate from 18 May to 9 August in four Michigan lakes of 80–200 acres (32–81 ha) left the autumn age-0 catch only marginally below that of control lakes (Beyerle & Williams 1967), and in 38 Midwestern ponds bluegill stocks of 112–168 kg/ha produced the most age-0 fish, with fewer at both lower and higher stocks (Novinger & Legler 1978; both via Neuswanger et al. 2015). For black bass a Michigan review found "no strong relationship between stock size and number of recruits, except at very low levels" (Bremigan et al. 2008), and in six 0.4-ha ponds adult numbers did not predict October age-0 numbers (Allen et al. 2011). For smallmouth, the percentage of young surviving fell as egg or fry abundance rose at Nebish Lake (Serns 1984), in Opeongo's Jones Bay (Friesen 1998) and at South Branch Lake, Maine (Neves 1975), and in an Ontario habitat model more nests gave fewer age-1 recruits per nest (all via Chu 2001); a model with cannibalism and food competition was Beverton–Holt-like at low density and Ricker-like at high density (Dong & DeAngelis 1998). Density-dependent growth appeared in 9 of 16 long-term populations and alone can regulate a population in a simple model (Lorenzen & Enberg 2002, abstract).

Where cannibals dominate, recruitment can cycle rather than settle: yellow perch in oligotrophic Crystal Lake, Wisconsin, formed three roughly five-year episodes of two dominant age classes (Sanderson et al. 1999), and in theory the smallest prey a cannibal can take decides between regulation and single-cohort cycles (Claessen et al. 2002). Over 40 years at Windermere, perch egg production varied twofold but age-2 recruits 300-fold (Craig & Kipling 1983, abstract). Pike recruitment followed a Ricker relationship with a temperature term at Windermere (Edeline et al. 2008), while another analysis found pike recruitment varying 16–27-fold with no stock–recruitment relation (Paxton et al. 2009, abstract), and stocking fry into self-reproducing lakes did not raise year-class strength (Hühn et al. 2014, 2023, abstracts). For the sea-run alewife, Love Lake's emigrants correlated with escapement over 11 years (Havey 1973, via Fay et al. 1983), whereas in Damariscotta Lake juvenile numbers were "controlled by competition for zooplankton" rather than by parental stock (Walton 1987, via ASMFC 2009). Taken together, the evidence suggests that recruitment in the Hot Brook lakes is set less by the number of eggs laid than by spring and nest temperatures, the overlap of larvae with their predators, crowding in the first summer and the length of the first winter (project synthesis). Section 5 describes how these stage-by-stage field values became targets for the model's young-of-year schools.

3.7 Predation and the food web

The Hot Brook lakes have two large piscivores, the chain pickerel and the smallmouth bass. Larger perches also eat fish: in summer, fish made up about 46 % of the food volume of yellow perch 16–35 cm long in Maine lakes, and 26 % of that of white perch of 15 cm and more (Cooper 1941). Northern pike and largemouth bass are not recorded in the lakes. They appear below as surrogates or contrasts. No predation measurement of any kind exists for the Hot Brook lakes: no stomach samples, predator densities, consumption estimates or prey mortality rates. This section therefore draws on other waters, and its Maine diet evidence comes almost entirely from one survey made in 1940 (Cooper 1941). Two properties of the lakes bear on nearly every mechanism discussed here. They are shallow and unstratified, so open water is never far from the weed edge. Their water is moderately colored, with a Secchi depth expected at roughly 3.5–4.5 m (Section 2), so color rather than suspended sediment limits how far a predator can see.

3.7.1 Finding, striking and catching prey

The two resident piscivores hunt in different ways. Esocids lie in ambush. Pike stayed motionless for more than 70 % of the time they were in visual contact with prey (Savino & Stein 1989). In Lac Ste. Anne, Alberta, they moved more than 5 m in only 16 % of 5-minute intervals in summer overall: 22 % around sunrise, 17 % by day, 21 % around sunset and 2 % at night (Diana 1979a). Smallmouth bass rove. Adults tracked in a Tennessee reservoir (12 tagged, 4 followed for activity) moved for 6.7 h a day at about 4.2 m/min, covering 0.8–3.5 km, and were most active in the afternoon (Bevelhimer 1995). No telemetry study has described the chain pickerel's diel activity. In West Virginia they fed at all hours (Lewis 1971, via Crossman & Lewis 1973). In the laboratory, a pickerel opened its strike from about 0.37 body lengths with a fast S-start and reached the prey in about 0.09 s (Rand & Lauder 1981).

Esocids and black bass react to prey fish 1–1.5 m away in clear water by day. A 29-cm largemouth reacted to a 5-cm bluegill at about 1.1 m (Howick & O'Brien 1983), and adult smallmouth reacted at 0.84–1.08 m at peak (Michels 2020). Reaction distance levels off at a few lux. Largemouth foraging success stayed above 95 % from low daylight down to moonlight (3 × 10⁻³ lx) and was 62 % under starlight (2 × 10⁻⁴ lx) (McMahon & Holanov 1995; abstract via a search summary). Prey see predators too. In bright light, bluegill saw an approaching bass from farther away than the bass saw them, but below about 5 lx the advantage passed to the bass (Howick & O'Brien 1983). Attacks on schooling marine silversides peaked in civil twilight (Major 1977).

Brown water reduces esocid feeding less than its color suggests. Young-of-year pike ate as many roach in water stained to a visual range under 5 cm as in clear water, perhaps because humic stain absorbs light rather than scattering it (Nilsson-Örtman et al. 2026). The notes assume a color of 30–60 mg Pt/L for Hot Brook. At that color they infer reaction distances of 1.0–1.2 m for pickerel and 0.8–1.0 m for smallmouth (project estimate). Temperature may matter more than color. Pike attack rates on brown trout fell sharply below about 11 °C (Öhlund et al. 2015; abstract only). In a Penobscot River reservoir, chain pickerel and smallmouth were the only predators of 390 tethered salmon smolts. The probability of predation within a one-hour deployment rose from about 10 % at 5 °C to 33 % at 15 °C, and was above average within 40 m of shore (Mensinger et al. 2025; abstract only).

Success per strike depends on the prey's shape, size and behavior (Table 3.7-1). Soft-rayed, fusiform fish are caught on most strikes. Esocids catch deep-bodied, spiny sunfish on about one strike in seven, though largemouth take small bluegill easily. No capture rate has been measured for any esocid or bass attacking yellow or white perch. The notes' working values for esocids are 0.3–0.4 per strike on yellow perch, 0.25–0.35 on white perch and 0.10–0.15 on pumpkinseed (project estimate).

Table 3.7-1. Capture success per strike in experiments (laboratory or pools).

Larger prey are harder to catch and slower to handle. For juvenile bluefish (a marine surrogate), capture success fell linearly with the prey-to-predator length ratio r. It was about 1.01 − 0.98r for soft-rayed anchovy and 0.70 − 1.34r for age-0 striped bass, a Morone like white perch (equations matched to prey species by the notes' reading of the paper). Handling time rose from 3–7 s at r = 0.2 to 10–22 s at r = 0.4 (Scharf et al. 2003). Given prey of equal length, small largemouth took longest to handle crayfish, followed by bluegill, yellow perch, stickleback, minnows and tadpoles (Hoyle & Keast 1987; abstract only). Spines protect bullheads. In aquaria, a pike that readily ate green sunfish would not attack bullheads. The only pike that ate a bullhead did so after other food ran out, and it died when a pectoral spine punctured its stomach (Beyerle & Williams 1968).

Schooling protects prey against bass and perch, but apparently not against esocids. Pike caught roach at the same rate whether the roach were single or schooled, while the success of Eurasian perch fell from 0.20 to 0.03 (Turesson & Brönmark 2004). Largemouth trials ending in a capture fell from 100 % with one prey to 11 % with 15 (Landeau & Terborgh 1986, via a secondary source). Vegetation reduces encounters and the decision to attack, not success per attack. Largemouth attacked bluegill about 31, 26, 3 and almost 0 times an hour at 0, 50, 250 and 1,000 rope stems/m², while success per attack stayed between 0.58 and 0.83 (Savino & Stein 1982). In Michigan field enclosures, bass ate 0.15 bluegill per bass per day in natural weed of 113–203 stems/m², against 1.5 where the weed had been cleared (Smith 1995).

All the laboratory rates above were measured within feeding bouts at 1–10 prey/m³. No field study has counted strikes or kills per hour for wild bass or esocids (project notes). Field rates are far lower, because prey leave predator habitat or hide. After pike were introduced to a Wisconsin lake, prey lost to emigration at least equalled prey eaten while prey biomass exceeded 40 kg/ha (He & Kitchell 1990; abstract only). Small bluegill confined to vegetation by bass got about a third of the open-water foraging return and grew 27 % less (Werner et al. 1983; abstract only). In 14 small central-Ontario lakes, fathead minnow, pearl dace, Phoxinus and brook stickleback were absent from every lake with smallmouth, while pumpkinseed and yellow perch remained (MacRae & Jackson 2001). Lakes with bass keep the prey that are hard to catch.

3.7.2 Gape and prey size

Field piscivores take prey far smaller than they could swallow. Across seven piscivores, in data including 784 pike and 201 smallmouth diets, median prey length was 10–20 % of predator length and the maximum 32–46 % (Gaeta et al. 2018). On their smallmouth regressions, bass of 200, 300 and 400 mm take median prey of about 50, 54 and 62 mm (project calculation). On published gape and body-depth regressions, a 300-mm smallmouth can swallow a pumpkinseed up to about 94 mm long (Fernando, Hecke & Eggleton 2018). Chain pickerel lack the semi-rigid cleithral ring of the basses and can swallow any fish no deeper-bodied than themselves. At 32 cm (12.5 in), the largest bluegill a pickerel could swallow was 35 % of its own length and the largest golden shiner 54 % (Lawrence 1960).

Field pickerel took much smaller prey. Florida adults averaging 50 cm ate prey averaging 15 cm (Buntz 1966). The white perch in Cooper's Maine stomachs were mostly 7–10 cm long (project estimate from Cooper's volumes). For a 35-cm Hot Brook pickerel, the notes infer typical prey of 5–11 cm and a ceiling of about 15–17 cm for perch-shaped prey (project estimate). Yellow perch of 8–13 cm therefore fall well within its range. Deep-bodied, spiny prey outgrow size-limited predators early: bluegill become relatively invulnerable to pike and largemouth beyond 100–125 mm (Schneider & Breck 1997).

3.7.3 Field rations, meals and consumption

Wild piscivores feed in meals and spend much of their time with empty stomachs (Table 3.7-2). Diana (1979a) studied 1,290 pike in Lac Ste. Anne. Their meals came 2.7–2.8 days apart in summer and about 25 days apart in winter, when gastric evacuation slowed from 48 h to 12 days. In summer, 3-year-old pike of 0.9–1.2 kg ate about 1.0–1.6 % of their body weight a day (%BW/d), and females ate 1.5–2.3 times as much as males. About 65 % of the year's energy gain came between May and July (Diana 1979a; thesis read by a sub-researcher). Diana (1983; abstract only) later judged these field rations probably inaccurate. Gill-net samples also overstate meal intervals: 48–50 % of gill-netted pike in Scottish lochs had regurgitated, and fewer than 10 % were truly empty (Treasurer 1988, via a secondary report).

Table 3.7-2. Field feeding indicators for piscivores.

For chain pickerel, no ration, meal interval, gastric-evacuation rate or ratio of consumption to maximum consumption (p) has been published (project notes). No pickerel ration or evacuation rate had been published by 1973 either (Crossman & Lewis 1973). Buntz's (1966) Florida pickerel fed less in summer: more than 75 % held food in January against 3–5 % in July. Scaled from the pike record, a 40-cm pickerel should take 0.4–0.8 fish a day, a meal every 2–3 days. A 30–35-cm smallmouth in July–August should take about one fish a day (range 0.3–2) among one to four items of all kinds (project estimates). Nesting largemouth males in Oklahoma stopped feeding for about 5–7 weeks (Zweiacker & Summerfelt 1974). Across studies, 35 % of diurnal piscivores had empty stomachs, against 16 % of fishes as a whole (Arrington et al. 2002). Field intake stays far below gut capacity. Across 38 wild species, predators carried two to three times the digestive capacity their mean intake needed (Armstrong & Schindler 2011; abstract only). Evacuation speeds up with temperature. A 550-g smallmouth clears 90 % of a 4-g fish in 18.7 h at 16 °C and 5.6 h at 24 °C (Rogers & Burley 1991, as modified by Fritts & Pearsons 2004). In yellow perch, crayfish meals clear 1.7–2 times more slowly than fish meals (Schneider 1973c).

At the population scale, Mille Lacs smallmouth ate about 0.87 kg of food per bass a year and pike 2.1–2.3 kg each (Ahrenstorff & Holbrook 2016; per-fish values are a project calculation). Bioenergetics fits put p at 0.26–0.30 for smallmouth in Smith Mountain Lake, Virginia (Moore 1988), and 0.39–0.44 for largemouth in a Washington reservoir, both known only second-hand via Wolf et al. (2022). These values depend on the model used. Overwintering largemouth needed p = 0.62 on the original model but 0.37 once heart-rate and accelerometer loggers had set their activity (Reeve et al. 2025). The esocid bioenergetics model overestimated the consumption of young tiger muskellunge by 113–328 % at 7.5–10 °C (Chipps, Einfalt & Wahl 2000; abstract only).

3.7.4 The seasonal cycle and winter feeding

Consumption is concentrated in the warm months. Pike rations peaked in June, and both sexes fasted at spawning (Diana 1979b). Largemouth rations rose from near zero in mid-May to more than 5 %BW/d in late August (Cochran & Adelman 1982; abstract only). Maine's bass plan puts the end of smallmouth feeding and growth near 10 °C (Jordan 2001). In Lake Opeongo, autumn was the season of greatest energy gain, and moving deeper may have let the bass keep foraging at 10–15 °C (Suski & Ridgway 2009). Males' muscle lipid in autumn was about 1.5 times the spring value (Mackereth, Noakes & Ridgway 1999), and the notes infer that adults spend about half of their autumn lipid by May (project estimate). Guarding males eat little but rarely nothing: 64 % of guarding Opeongo males held prey (Steinhart et al. 2005).

Winter separates the two Hot Brook piscivores. Maine anglers caught 0.46 bass (smallmouth and largemouth together) per angler-day through the ice against 1.7 in open water, and in Washington and Hancock counties bass are almost never caught in winter (Jordan 2001). Wild largemouth in Warner Lake, Ontario, lost 3.6 % of their mass between November and June, most of them feeding a little all winter and some fasting (Reeve et al. 2025). Warner Lake's prey community resembles Hot Brook's. Pickerel feed through the winter. Maine anglers caught 1.18 pickerel per angler-day through the ice against 0.49 in summer (Brokaw 2001). In a Nova Scotia lake, tagged pickerel kept moving at a low level all winter, while the lake's smallmouth sat nearly still at four wintering sites (Sergio 2026). Winter rations are still small: with 12-day gastric evacuation, a pike can take only about 0.25–0.4 %BW/d (project estimate from Diana 1979b). No under-ice stomach data exist for chain pickerel anywhere in the Northeast. The one Maine study of spring pickerel food (Warner 1973) has been seen only in its introduction.

3.7.5 Diets in Maine and elsewhere

Apart from Warner's (1973) spring pickerel study, whose data pages have not been seen, the only Maine diet-composition data for adults of either piscivore are Cooper's (1941), from lakes in the Androscoggin and Kennebec drainages sampled in 1940 (Table 3.7-3). The fish came from 86 sets of paired gill nets fished between 15 June and 11 September, almost all overnight and mostly at 3–15 m. The pickerel sample also includes 32 fish taken at Pushaw Pond (Penobscot County) in October, which supplied all the table's bullhead and its single cannibalized pickerel. The white perch eaten were mostly 7–10 cm long, which means yearlings in summer and young-of-year in October (project estimate from Cooper's volumes). The bass took no smelt although smelt were present. None of 1,757 white perch, 66 bass or 110 pickerel stomachs held a white sucker. Cooper noted that "crayfish are generally rare in Maine", and found one crayfish in 809 bottom samples.

Table 3.7-3. Summer food of chain pickerel (with one October sample) and smallmouth bass in Maine lakes, percent of food volume (number of items in brackets) (Cooper 1941; percentages computed from Cooper's volumes).

Cooper's samples are small and dominated by a few lakes: one Snow Pond sample supplied 86.5 of the bass's 145.5 mL of white perch. They are gill-netted and almost all from summer, and they come from lakes with golden shiner and rainbow smelt, which Hot Brook lacks. The white perch counts give a floor of 0.12–0.25 white perch per predator per day (project estimate). MDIFW lists yellow perch, white perch, sunfish, minnows and smelt as the pickerel's principal prey, and pickerel become strongly piscivorous from 18–23 cm (7–9 in). Pickerel also take stocked salmonids. These were in 15 of 54 pickerel (28 %; mean length 43 cm, 16.9 in) after a brown trout stocking in Brandy Pond, the smallest trout-eater 38 cm (15 in), and in 21 % of pickerel over 25 cm (10 in) during a salmon smolt run in Beddington Lake (Brokaw 2001). The MDIFW bass plan states that the link between forage species and bass growth in Maine is unknown (Jordan 2001). At Hot Brook, an angler reports that crayfish are not common (project field notes).

Elsewhere, adult pickerel are mainly fish-eaters where small fish are available. In 12 Connecticut and Massachusetts lakes the diet was about 75 % fish, 20 % crayfish and 5 % small invertebrates, with sunfishes 45–62 % of the fish eaten (Brodersen, Howeth & Post 2015). In Wentzells Lake, Nova Scotia, it was about 85 % fish by weight, and white perch were the second fish prey (Feener & MacLeod 2020). Isotopes from Kejimkujik lakes attribute about 74 % of the diet of 4.2–10.9-cm pickerel to dragonfly and damselfly larvae, and about 72 % of the diet of 20.2–58.6-cm fish to fish (Swinemar, Campbell & Reid 2024; abstract only). Where small fish are scarce, adults fall back on insects. In three small Nova Scotia lakes with introduced pickerel and almost no small fish left, 10 of 17 pickerel stomachs held insects and 2 held fish (Mitchell, LeBlanc & Heggelin c. 2011).

Smallmouth diets depend on what the lake offers. On rocky Ontario shores with about 6 crayfish/m², crayfish made up 72–79 % of food volume (Tester 1932). They also made up 71 % of the diet of Opeongo bass over 25 cm (Dunlop et al. 2005). Yet bass do not prefer crayfish when fish are available. Adult smallmouth offered crayfish, golden shiner and round goby avoided crayfish or showed no preference for them in every treatment (Carter et al. 2010; abstract only). Where crayfish are scarce, bass turn to insects rather than fish. Insects made up 61–72 % of bass stomach contents (juveniles and adults pooled) in Provoking Lake, Ontario, where bass growth fell behind at the size at which Opeongo bass switch to crayfish (Dunlop et al. 2005). In 85 bass from Wentzells Lake, more than 99 % of the diet by weight was invertebrates (Feener & MacLeod 2020). In 13 Nova Scotia lakes the bass were thin. Every population with an asymptotic length under 50 cm but one shared its lake with chain pickerel, which the authors read as competition between the two littoral predators (MacMillan et al. 2002). Pike, the surrogate for pickerel, also depend on perch. In six Voyageurs National Park lakes their diet was more than 60 % fish by mass, mainly yellow perch, in every season (Soupir, Brown & Kallemeyn 2000).

Young piscivores pass through invertebrate stages first. Chain pickerel eat plankton, then insects, and fish become their main food at 102–152 mm (Scott & Crossman 1973). Young smallmouth in Lake Opeongo first took fish at 10–15 cm (Dunlop et al. 2005). How their kill rate responds to prey density is known only from surrogates. The response is usually type II, rising to a plateau, in experiments with juvenile largemouth (Alexander et al. 2015; Cuthbert et al. 2020; abstracts only) and young-of-year pike. Pike, however, gave a dome-shaped response at 5 °C in clear water (Nilsson-Örtman et al. 2026). Attack rate peaks at an intermediate prey size: 0.19 of predator length for pikeperch (Persson & Brönmark 2002). Tank clearance rates of 6–19-cm marine predators on fish larvae, sustained all day, would reach 24–140 m³ d⁻¹, against 3–10 m³ d⁻¹ in estimates from lakes and large enclosures (project estimate). In the field, young largemouth at about 442/ha consumed 58–93 % of the littoral bluegill fry in an Illinois lake (Santucci & Wahl 2003, via a secondary review).

3.7.6 Predation mortality of the prey

How much of a perch population the piscivores remove is known only indirectly. In lightly fished small lakes with esocids or bass, yellow perch of 7.5 cm and more lose about 35–70 % of their number a year. In unfished Mill Lake, Michigan, which held largemouth and pike, the loss was 70 %, all from natural causes (Schneider 1973a). In Wisconsin's Murphy Flowage, natural losses were about 55 % (Snow 1978; values decoded from poor optical character recognition). The notes judge that fish predation removes roughly 15–35 % a year of perch 7.5–15 cm long, less above 18–20 cm, and that birds add perhaps 5–10 % (project estimate). Cormorants alone took 7.7 % of Oneida Lake's adult perch a year (Rudstam et al. 2004; abstract only). In 18 Sudbury-area lakes recolonized by pike, walleye and smallmouth, perch biomass per gill net averaged 357 g where predators were established and 695 g where they had recently returned, against 1,497 g where they were absent. With predators, perch switched to bottom prey at 83 mm instead of 140 mm (Lippert, Gunn & Morgan 2007). Smallmouth consumed 1–34 % of age-0 perch production in South Dakota glacial lakes (Dembkowski et al. 2015; abstract only). No perch mortality estimate exists for any Maine lake, and pickerel consumption of perch has never been measured (project notes).

Predators matter most to white perch at small sizes. In Oneida Lake, the winter mortality of age-0 white perch tracked total predator biomass (Fitzgerald et al. 2006; abstract only). In a non-stunted Nebraska lake, every white perch eaten by predators was immature (Gosch, Pierce & Pope 2010; abstract only). Their importance as prey differs enormously between waters. In Kerr Reservoir, on the Virginia–North Carolina border, where shad were available, white perch were under 2 % by weight of every sportfish diet (Harris 2006). In Maine they made up 55–61 % of pickerel and bass food (Cooper 1941). Cooper's age frequencies show many Maine white perch surviving to 8–10 years. A widely used species profile links stunted white perch populations to a scarcity of predators (Stanley & Danie 1983).

Small-bodied species can be eliminated where they meet a new predator. Three small Nova Scotia lakes with introduced pickerel held only pickerel and large white suckers. Catches there were 0.047 fish per trap-hour against 1.04 in pickerel-free lakes, although the communities before the introductions are unknown (Mitchell, LeBlanc & Heggelin c. 2011). Removing more than 90 % of an Adirondack lake's smallmouth raised six littoral species 4–90-fold within two years (Weidel, Josephson & Kraft 2007; relayed by a search summary). Hot Brook shows long coexistence instead. MDIFW recorded banded killifish with chain pickerel in the lakes in 1949 and in 2024, so the killifish have persisted alongside pickerel for at least 75 years (project notes).

3.7.7 Chain pickerel population dynamics, mortality and cannibalism

No published catch curve, tagging study or mark–recapture survival estimate has been found for chain pickerel in any northeastern lake. The key early study, of an exploited and an unexploited Rhode Island pond (Saila 1956), could not be read (project notes). Wild pickerel typically live 3–4 years, at most about 9 (Animal Diversity Web; FishBase; New Jersey Division of Fish & Wildlife). Estimates of natural mortality M disagree widely. Growth parameters give 0.24–0.41 yr⁻¹ (Then et al. 2015 estimator) and maximum age gives 0.65–0.73. Body size gives 1.9 yr⁻¹ at 10 cm, falling to 0.50 at 43 cm (Lorenzen 1996) (all project calculations). Across Ontario lakes, northern pike of age 5 and over lose 36 % a year in females and 51 % in males (Malette & Morgan 2005). From these figures the notes set survival for a lightly fished Maine population at 0.55–0.70 for adults of 33 cm and over, 0.50–0.60 at age 2 and 0.40–0.50 at age 1 (project estimate).

Angling is a small part of adult pickerel mortality. In 1999 Maine anglers caught about 1.19 million pickerel and kept 0.133 million, releasing 79 % of the winter catch and 94 % of the summer catch. MDIFW lists the low harvest, which leaves many pickerel to die of natural causes instead, among its management problems (Brokaw 2001). The implied angling mortality is about 0.03–0.05 yr⁻¹ (project estimate). Pickerel density is equally uncertain. The only Maine counts come from rotenone censuses of two small, fairly deep lakes regarded as potential trout water. One held 83 pickerel/ha and 4.1 kg/ha (a minimum) and the other 175/ha and 8.4 kg/ha, with fish averaging under 50 g in both (Rupp & DeRoche 1965; per-hectare values are a project conversion). Grass pickerel in a Wisconsin lake numbered 22–97/ha over four autumns; the decline was driven by year-class failure when drought stranded the nursery (Kleinert & Mraz 1966). Savanne Lake, Ontario, is close to Hot Brook in size and depth (364 ha, mean depth 2.6 m), and it held 6.9–7.2 mature pike/ha (Mosindy 1980; abstract only). The notes expect 15–40 pickerel of 8 cm or more per hectare and 2–6 kg/ha lake-wide at Hot Brook, concentrated in the weedy littoral (project estimate).

Cannibalism has never been quantified for chain pickerel. Among Kendall's (1917) Maine and New Hampshire stomach records, six of eight young pickerel of 108–162 mm, caught together at an unstated place, held fish, and four of those prey were smaller pickerel. In Kendall's records, pickerel prey reached 0.71 of the cannibal's length (project calculation). Cooper's single cannibalized pickerel came from the October Pushaw Pond sample. Stomach studies in Florida (Guillory 1979; Buntz 1966), New York (Raney 1942, known from secondary summaries) and Nova Scotia (Mitchell, LeBlanc & Heggelin c. 2011) recorded no cannibalism. In grass pickerel, 2 % of 351 young-of-year had eaten pickerel and no adult had (Kleinert & Mraz 1966). Among pike, cannibalism falls mainly on young-of-year and yearlings and can regulate density, but conspecifics are a minor part of the cannibal's diet (Persson, Bertolo & De Roos 2006; Craig 2008). In Swedish lakes, the fish prey of pike, conspecifics included, were 0.03–0.55 of the predator's length (Persson, Bertolo & De Roos 2006). The share of pond juveniles that became cannibals rose from 7.8 % to 41.3 % as larval density tripled (Bry et al. 1992; abstract only). Given the length limit, a 20-cm pickerel is at risk only from pickerel of 36–40 cm or more (project estimate).

Few predators take adult pickerel. In Maine, largemouth bass are serious predators of young pickerel in weed patches, and pickerel have declined in small waters where largemouth became established (Brokaw 2001). Age-0 pickerel may coexist better with smallmouth (Buck & Thoits 1967, via Crossman & Lewis 1973). No record has been found of smallmouth eating chain pickerel of 20 cm or more. In interior Maine, bald eagles favor chain pickerel among their freshwater prey (Todd et al. 1982; Section 3.8).

3.7.8 Where predators meet prey: depth and distance from shore

Predation requires predators and prey to overlap. In the smallmouth telemetry studies found, mostly from small lakes and reservoirs, summer adults stayed close to shore. In a Tennessee reservoir, adults stayed within 5 m of shore most of the time, usually in water under 2 m deep. They entered open water only to cross small embayments, did not move between inshore and offshore water by day and night, and rested beside fallen trees, logs and boulders (Bevelhimer 1995). In Milipsigate Lake, Nova Scotia, 79 % of June positions lay within 50 m of shore, a share inflated by nesting males (Sergio 2026). In Lake of Two Rivers, Ontario, summer bass stayed shallow and nearshore (Bloomfield et al. 2022). The only Maine telemetry found followed 44 bass in Green Lake in summer 1993. Large fish (over 406 mm) used water deeper than 8 m more often in late summer, and smaller fish used cover more (Cole & Moring 1997; abstract only). Pickerel stay shallower still. Half of the pickerel detections in Milipsigate were at 0.76–1.82 m, and the lake's smallmouth used water about three times deeper (Sergio 2026). At Hot Brook, a project analysis of the 1949 MDIFW soundings, fitted to today's shoreline, puts the first 25 m from shore on a shelf less than 1 m deep and the 2–3-m contour 50–150 m out. The nearshore bass habitat is therefore the slope from 1 to 3 m, 25–100 m from shore (project analysis). An angler reports smallmouth usually close to shore, with some in open water (project field notes).

White perch use the open, soft-bottomed basins of shallow lakes. In unstratified Missisquoi Bay, Lake Champlain, 3–5 m deep, white perch were 65.8 % of the fish in 24-h gill nets and were caught at all 14 open-bay stations. Shore seines at 0.5–2.5 m took them at only 8 of 27 stations. Pike, smallmouth and largemouth were netted at 11, 10 and 5 of the 14 open-bay stations (Bilodeau, Dumas & Massé 2004). In Cooper's Maine survey, white perch outnumbered yellow perch about 7 to 1 in overnight gill nets but were outnumbered about 4 to 1 in daytime shore seines (Cooper 1941). Young white perch under 100 mm were found only over unvegetated littoral bottom and moved shallow after dark (Harris 2006). In Maine, young of 2.5–7.6 cm come onto sandy beaches in the evening (AuClair 1958). The usual compiled diel pattern, 0.9–1.2 m at night and 4–9 m by day, comes from unnamed lakes (Stanley & Danie 1983). In water as colored as Hot Brook's, the same daytime light would lie at about 1.4–5.4 m, depending on the light attenuation assumed (project estimate). No telemetry, hydroacoustic or day-and-night net study of white perch depth or distance from shore has been found for any lake, and no study records where or when pickerel or bass catch them (project notes).

Adult yellow perch in simple basins school offshore by day. In South Dakota's Lake Madison they averaged 3.4 m deep and 344 m from shore in summer (Radabaugh 2006; abstract only). Under predation, small perch shift toward littoral habits, turning to bottom prey earlier and taking a littoral body form (Lippert, Gunn & Morgan 2007), and age-0 Eurasian perch used vegetation when pike were present (Snickars et al. 2004; abstract only). Plants at Hot Brook are thought to reach 3–3.5 m and the deepest water is 4–5.5 m, so the notes see little deep offshore refuge for perch there (project estimate).

3.7.9 Whole-lake energy flow

No production or consumption estimate exists for any fish population at Hot Brook, and no energy-flow model of a small north-temperate lake with bass, perch and pickerel has been found (project notes). Standing stocks give the scale. Maine's only rotenone censuses found 44.5 (a minimum), 70.1 and 117.1 kg/ha of fish in three small lakes with mean depths of 5–6 m, and in one of them 41 % of the weight was American eel (Rupp & DeRoche 1965). Lake Jesse, a shallow soft-water lake in Nova Scotia without bass or pickerel, held 22.3 kg/ha (Smith 1939). Richer Michigan and Florida lakes average roughly 100–130 kg/ha (Schneider 1973b; Bachmann et al. 1996). Piscivores make up about 10–21 % of fish biomass in Michigan lakes (project calculation from Schneider 1973b) and about 22 % (range 0–73 %) in Florida lakes (Bachmann et al. 1996). Total phosphorus is the best single predictor of fish biomass and yield (Hanson & Leggett 1982; abstract only).

Fish production scales with biomass and body size (Downing & Plante 1993), and community production averaged 82 kg/ha/yr in 22 lakes (Randall, Minns & Kelso 1995). Piscivores eat about three to five times their own biomass a year. Their consumption-to-biomass ratio (Q/B) is 4.07 for smallmouth in the Bay of Quinte food-web model (Blukacz-Richards & Koops 2012), 4.0 for gar, bowfin and chain pickerel in a Florida lake model (Rogers & Allen 2009), and 2.7–3.8 for Windermere pike (Johnson 1966; abstract only). The Bay of Quinte model, for part of Lake Ontario, shows the structure of such a food web. Its fish standing stock, about 165 kg/ha, exceeds zooplankton biomass, yet production still forms a pyramid. In g m⁻² yr⁻¹ (probably wet weight; the model's supplement does not say), production is about 2,650 for phytoplankton, 240 for zooplankton, 125 for bottom invertebrates other than dreissenid mussels, and 19.6 for fish. Those figures give transfer efficiencies of about 9 % from phytoplankton to zooplankton, 5.4 % from zooplankton and bottom invertebrates to fish, and 0.74 % from phytoplankton to fish (project calculations from the model's tables). Across studies, transfer to fish from zooplankton and bottom invertebrates is about 5–10 %, and along the whole chain from algae to fish it ranges from below 0.01 % to about 1 % (Mehner et al. 2022).

In small lakes much of this production rests on the bottom. Bottom invertebrates made up about 50 % of the prey of 470 fish populations, or about 65 % counting the bottom-feeding fish that piscivores eat (Vander Zanden & Vadeboncoeur 2002; abstract only). Across 546 fish populations in 75 lakes, reliance on littoral carbon averaged 57 % (lake means, each species weighted equally; Vander Zanden, Vadeboncoeur & Chandra 2011). In lakes with a mean depth under 4 m, stable isotopes cannot separate littoral from open-water carbon (Stasko 2013); both Hot Brook lakes are shallower than that on average. Crayfish can be a large link between the bottom and fish where they are common. In three Michigan lakes they stood at 46–213 kg/ha and produced 60–142 kg/ha/yr (Momot & Gowing 1977; abstract via a search summary). In Maine's soft-water lakes, however, the link appears weak (Cooper 1941; Section 3.4).

Applied to Hot Brook, the analog values give an order of magnitude only. Take pickerel at 3–8 kg/ha with a Q/B of about 3–4, lower than elsewhere because of roughly five months of ice. Pickerel would then eat about 1–10 kg/ha/yr of perch (central value about 3), removing some 10–40 % of the perch biomass aged 1 year and over each year (project estimate). A separate estimate takes pickerel at 4–8 kg/ha and smallmouth at 3–8 kg/ha. On those figures the two predators would eat 10–35 kg/ha/yr of white perch, about 1,200–4,400 mostly young fish per hectare a year, from a white perch standing stock estimated at 15–35 kg/ha (project estimate). Only two Hot Brook-related checks exist. MDIFW's statewide stock objective, which counts all of Hot Brook's water as bass habitat, is 2 bass longer than 10 in (25 cm) per acre, about 5/ha (Jordan 2001). An angler reports catching mostly white perch, with many fallfish and smallmouth and few pickerel (project field notes).

Fish-eating birds and mammals take a further share that has not been measured (Section 3.8). In interior Maine, fish made up 79 % of bald eagle prey items, with brown bullhead, white sucker and chain pickerel the favored freshwater foods (Todd et al. 1982). A pair of loons rearing two chicks removes about 423 kg of food over 5.5 months (Barr 1996; abstract only). An angler has seen bald eagles and a common merganser brood at the lakes (project field notes). Section 5 returns to the field rations, diets and shoreline habitat summarized here, which served as targets when the model's predation rules were revised.

3.8 Wildlife, amphibians, reptiles, insects and the forest

Almost none of the lakes' non-fish fauna, and little of their forest beyond mapped land cover, has been measured at Hot Brook. The site record is a handful of state map layers, museum specimens, citizen-science records and angler observations. Most values below therefore come from other Maine lakes or from farther afield, and each is labeled by where it was measured.

3.8.1 What is recorded at the lakes

MDIFW's records show a bald eagle pair at a nest on Upper in 2008, with one fledgling recorded in 2013 and eagles at the nest in July 2018. The Maine Bird Atlas (2018–22) confirmed eagle breeding in an atlas block covering part of Upper, and at least four other territories lie within about 20 km (MDIFW GIS map services; Maine Bird Atlas). Whether the nest has been active since 2018 is unknown. Atlas effort was otherwise thin: winter effort was 0–0.03 h in each of the four blocks over the lakes. Regional GBIF, eBird and atlas records (45.50–45.80° N, 67.75–68.10° W) measure observer effort rather than abundance. They include 47 common loon, 33 belted kingfisher, 12 American bittern, 10 osprey, 9 hooded merganser (with July broods) and 8 great blue heron records; two loons recorded in late May 2022 were very probably on Lower. No osprey nest is recorded at the lakes, and the heron has no breeding code in the six surrounding atlas blocks (project queries). MDIFW maps eight Inland Waterfowl and Wading Bird Habitat polygons around the lakes (MDIFW Wildlife Habitat Data map service). Angler observations (project field notes) add bald eagles, a common merganser brood in July 2026 (photographed), deer and black bear at the lakes, "definitely some bullfrogs", several other frogs and "some turtles". iNaturalist holds black bear, moose and fisher records from within a few kilometers of Lower (2020–21). The National Wetlands Inventory maps beaver-modified wetlands within 500 m of both lakes, with a cluster on Lower's outlet side, but these are photo-interpreted only. No river otter, mink, muskrat or raccoon record was found (project queries).

3.8.2 Fish-eating birds

Table 3.8-1 sets out each bird's foraging zone, food and spacing; the text gives the context.

Table 3.8-1. Fish-eating birds of Maine lakes, with the Hot Brook evidence. Sources as in the text.

Common loon. Maine loons return right after ice-out in April and nest in May–June on dead vegetation and mud at the shoreline, often on small islands. Chicks hatch after about 27 days and are reared through July–August; parents leave their territories to gather in rafts in September–October, loons winter on the coast from November to March, and juveniles first breed at about seven years (MDIFW & Maine Audubon n.d.). Of 26 nests in one study none lay more than about 1.2 m from water (Vermeer 1973). Nests are typically 5–20 cm above the water, and a motorboat passing at 15 m raises a wave of about 13–15 cm (Anderson 2025). A record 42 nests flooded in one recent New Hampshire year, and heavy rain is now a larger nest threat than predators in some years (Grant 2024, popular source). Territories average about 40 ha in Maine (Maine Audubon 2024) and about 72 ha in Wisconsin, where food may limit them (Barr 1996, abstract only). In northern Wisconsin, 96 pairs held whole lakes of 55 ± 36 ha, and 29 pairs held coves of large lakes of 358 ± 347 ha (Piper et al. 2018). At the Belgrade Lakes in 2019, 23 territorial pairs on two lakes of about 1,000 and 3,300 ha fledged 0.35 young per pair. Natural nests there succeeded in 22–54 % of attempts in four years between 2019 and 2024 (Belgrade Lakes Association 2019–2024). That spacing, one pair per 94–278 ha, implies roughly 1–4 pairs on Upper's 360–370 ha (DEP and MDIFW acreages; project arithmetic). No pair or chick count was found for either lake, and both lie north of Maine Audubon's count area (south of 45° N). That count's estimate for 2025 was 3,174 adults and 568 chicks, more than double the 1983 count (WBUR/AP 2025).

In Wisconsin, loons mostly take whatever fish is easiest to catch, "often yellow perch". A pair rearing two chicks removes about 423 kg of food in about 5.5 months, and loons do not appear to harm sport fisheries (Barr 1996, abstract only). Doubly labeled water on Wisconsin chicks showed them using 686–1,935 kJ a day between 10 and 35 days of age, eating 162–383 g of fish a day (Fournier et al. 2002). Barr's total implies about 1.1 kg a day per adult, 20–25 % of body mass. By Barr's total, one pair with two chicks would remove about 1.2 kg/ha/yr on Upper (about 365 ha), roughly 1–2 % of a 60–150 kg/ha fish stock that is itself a working estimate; the 360–900 kg range of popular estimates gives 1–2.5 kg/ha/yr and 1–4 % (project estimates). No measured daily intake of wild adult loons was found.

Herons and kingfishers. Great blue herons fish clear water usually ≤ 50 cm deep and take fish up to about 25 cm (Short & Cooper 1985); their winter range begins at the southern New England coast (AOU 1983, via Short & Cooper 1985). At a trout tailwater, 56.4 % of strikes succeeded, 86.9 % of captures were in ≤ 20 cm of water and 87 % of prey were ≤ 14 cm (Hodgens et al. 2004). Captive herons needed about 300 g of live fish a day (Glahn et al. 2000). Maine herons are noticed from mid-March and reach their colonies in early to mid-April. In 2022, 55 of 105 surveyed colonies were active with at least 469 nesting pairs, and the species is of Special Concern (MDIFW HERON n.d.). Belted kingfishers take fish usually ≤ 10 cm, in water < 60 cm deep and probably within 12–15 cm of the surface. Michigan lakeside territories averaged about 0.8 km of shore and "invariably included" a sheltered bay, and kingfishers increased where beaver ponds opened overgrown streams (Prose 1985). In Maritime lakes, ninespine sticklebacks dominated kingfisher diets, with white perch and alewife also eaten; banded killifish were 10.5–18.7 % of pellet items at three Maritime lake and river sites (White 1953). Wintering California kingfishers used 70.2 kcal a day (Forsell 1983), about 60–75 g of fish (project estimate).

Osprey and bald eagle. Ospreys nest statewide and take only live fish (Maine Rivers n.d.). At a coastal Maine nest the first adult returned on 6 April (2014) and the young left in early September (Journey North n.d.). Chesapeake nests received 5.4 fish a day averaging 156.9 g (McLean & Byrd 1991), and an osprey-cam page puts an adult's need at about 300 g a day without stating its basis (VIMS n.d.). In California, 82 % of fishing efforts succeeded (Ueoka & Koplin 1973). One nest fishing Upper would remove about 0.2 kg/ha/yr (project estimate). Interior Maine bald eagles took fish as 79 % of prey items, chiefly brown bullhead, white sucker and chain pickerel (Todd et al. 1982). Many inland eagles stay through winter and scavenge more when the lakes are frozen (MDIFW n.d., bald eagle page). Maine held 733 pairs in 2018, up from 21 in 1967 (MDIFW 2018). A wild 4.5-kg eagle wintering in Washington needs about 494 kcal (2.07 MJ) a day, roughly 500 g of chum salmon (Stalmaster 1981; whether measured or modeled is not recorded in the notes). Spawning runs draw both birds. Up to 5 ospreys and 3 eagles a day attended the Nequasset alewife run in 2024 (kennebecestuary.org daily log 2024). At Grand Falls on the St. Croix, 20–40 eagles a day gathered until the 1995 fishway closures (IJC St. Croix River Board 2005). Sea-run alewife are now recorded for Lower (Section 3.5).

Mergansers and cormorants. Breeding hooded mergansers rose to 23–29 per 100 km² on an untrapped south-central Maine site as beaver wetlands expanded (McCall et al. 1996). Captive female common mergansers needed 255–285 g of trout a day, about 30 % of body mass, and preferred 10–13 cm prey (Latta & Sharkey 1964, abstract only). Cormorants ate yellow perch as 40–80 % of their diet at Leech Lake, Minnesota (Göktepe et al. 2012). At Oneida Lake they removed 7.7 % of the adult yellow perch a year (Rudstam et al. 2004, abstract only). Fish-eating birds are also the final hosts of black spot (the belted kingfisher), yellow and white grubs (the great blue heron) and swimmer's itch (the common merganser), none of them documented at Hot Brook (Hoffman 1999; Rudko et al. 2019). Heavy black-spot loads cut young fish's first-winter survival (Lemly & Esch 1984).

How fish respond. In Oklahoma and Panama streams, fish over 3 cm avoided water < 20 cm deep. All six catfish tethered at < 18 cm were taken within 24 h, while 10 of 14 survived deeper, and adult stonerollers moved into < 20 cm shoals within hours once bass were added (Power 1987). In Tennessee, pool depth predicted the size of the largest fish (Harvey & Stewart 1991). Herons and raccoons took crayfish tethered in 5–15 cm of water but few in 40–70 cm (Englund & Krupa 2000). Together these imply that bird risk for fish of about 5–7 cm or more is high in < 20 cm by day, falls to near zero below 50–60 cm, and peaks at dawn and dusk (project estimate). The brook's pools, 0.9–1.2 m (3–4 ft) deep (angler observation), lie beyond heron and kingfisher reach. That may help explain why sunfish hold there (project estimate). None of these studies is from Maine, and none concerns loons, ospreys or mergansers.

3.8.3 Semi-aquatic mammals

Maine river otters eat mostly slow fish such as suckers and minnows, plus crayfish (MDIFW n.d., river otter page). They take prey in proportion to its availability and inversely to its swimming ability, are active all year, feed most from dawn to mid-morning, and shelter in beaver lodges. A 16-km Idaho stream held 4–7 otters. Maine's carrying capacity was put at about 20,000 otters on 21,541 habitat units, each equivalent to a mile of top-quality shore (MDIFW 1986). In Arkansas, a 7.84-kg otter used 4,738 kJ a day, or 35–53 kg of wet prey a month. Crayfish were in 85 % of summer scats and fish in 58 % of winter scats (Dekar et al. 2010). Mink are chiefly nocturnal. They eat fish in winter and spring, crayfish in summer and small mammals in autumn, typically work no more than about 300 m of shore a day, and reached densities of 1.5 to over 3 per km of shore on the Vancouver Island coast (Allen 1984). A wild mink needs about 150–300 g of food a day (project estimate from farm-mink maintenance energy). Raccoons are the main predators of turtle nests (Section 3.8.5). They were 97 % nocturnal in Germany (Michler 2016) and numbered 0.8–18.3 per km² in western Tennessee (Leberg & Kennedy 1988); no Maine density was found.

Beavers engineer the wetlands. On an untrapped south-central Maine site, colonies rose from 0.15 to 0.32 per km² in 1988–92, and open water rose by 36 %; wetland area tracked colony density (r = 0.99). A trapped site held 0.19–0.20 colonies per km² (McCall et al. 1996). Favorable habitat holds 0.4–0.8 colonies per km², mostly on stream gradients under 6 %, and most cutting is within 30 m of water (Allen 1982). Any present-day control on the Hot Brook outlets is probably beaver-made (project inference). Muskrats need slow wetlands with emergent cover (cattail, bulrush, sweetflag, arrowhead, wild rice or sedge) over about three-quarters of their area, and can eat out their own food (MDIFW n.d., muskrat assessment).

3.8.4 Forest mammals: black bear, white-tailed deer and moose

The lakes lie in Wildlife Management District (WMD) 11, about 4,580 km² (1,769 mi²). Maine holds about 27,000 black bears (agency range 24,000–36,000) on about 85 % of the state (secondary sources). That is about 0.40–0.53 bears per km² of occupied range (project estimate). Hair-snare surveys in New York gave 0.14–0.20 per km² (Gardner et al. 2010; Sun et al. 2017). The 2019–25 bear harvest ran 5–14 a year in Danforth, 2–9 in T8 R4 NBPP and 0–15 in Bancroft (MDIFW harvest records compiled in the project notes). Adult females range over 15.5–23 km² and young males up to 260 km² (Mackowski 2011). Bears enter their dens from mid-October to late November and emerge in late April (MDIFW species sheet, via a search summary). Animal matter is under 10 % of the annual diet, and spring foods include fawns in late May–June (Bangor Daily News 2025; North American Bear Center n.d.). Near Ely, Minnesota, bears ate no fish unless they lived by a stream where white suckers spawn (North American Bear Center n.d.). No study quantifying bears eating suckers was found. A spring bear needs 16–23 MJ a day; taking half of that from suckers would mean 2–3 fish a day, or 15–60 over a run (project estimate).

Deer in WMDs 1–11 numbered 2–6 per mi² (0.8–2.3 per km²) after the hunt. That is below the long-term goal of 10 per mi² because of poor habitat and hard winters (MDIFW, LD 1569 §3 goals and agency statements, via a search summary). Deer yard in dense softwood when snow exceeds about 30 cm and the mean daily temperature is below 0 °C; dense conifer holds up to 40 % less snow (MDIFW n.d., significant wildlife habitat, via a search summary). Two mapped deer wintering areas, of about 1,640 and 143 ha, lie within about 3 km of the lakes (MDIFW Wildlife Habitat Data map service). Deer also crop aquatic plants in late spring and early summer, most when water is low, but the aquatic share of their diet is "unknown but probably low" (Rogers et al. 1981).

Helicopter surveys found 0.4–4.0 moose per km² across nine northern WMDs (Kantar & Cumberland 2013, abstract only). WMD 11 was flown in 2011–12, but no figure for it was found (MDIFW 2013). The district is managed as a "compromise zone" with fewer moose, and permits were cut after the 2012 census (Latti 2012). Danforth's moose harvest fell from 9 a year (2009–10) to 0–1 (2019–25), a fall driven by permits rather than density (MDIFW harvest records). Moose feed heavily in lakes. On Isle Royale they fed in water on 108 of 124 summer days; they were mostly nocturnal in summer, with a separate late-afternoon peak of aquatic feeding, and cows fed in water 1.65–1.93 times as often as bulls. An adult ate 868 g dry of aquatic plants a day, cropping 20.3 g dry a minute in dives of about 16 s. That was 17.7 % of dry intake, or about half of wet intake (project arithmetic). The pond diet was 58 % stoneworts and 15.5 % Potamogeton. Six moose removed about 17 % of a 2.5-ha beaver pond's aquatic production, and none was seen to defecate in 65 h in ponds, so moose carry aquatic nitrogen and phosphorus to land (Belovsky & Jordan 1978; pond area and percentage by project arithmetic). Aquatic plants supply sodium and leaves supply energy (Belovsky 1981; Botkin et al. 1973, abstract only). In Ontario, the lakes moose used heavily were shallower, with mineral-rich sediment (Fraser et al. 1984, abstract only). In a large, heavily used lake in Sibley Provincial Park, Ontario, Nuphar variegata and Potamogeton filiformis "largely disappeared", and Nuphar returned as moose declined (Fraser & Hristienko 1983, abstract only). Stoneworts are the only plants ever collected in the Hot Brook lakes (Section 3.4).

3.8.5 Turtles

The painted turtle is common across Maine except the north-west, living in permanent water with submerged plants and basking sites (MDIFW n.d., painted turtle page). It feeds and breeds once body temperature exceeds 15–20 °C. The young are mainly carnivorous and adults mainly herbivorous, and Algonquin adults foraged on land for odonate larvae, probably emerging ones (COSEWIC 2018; Moldowan et al. 2015). Densities span two orders of magnitude (Table 3.8-2), with 6.5–10 per ha in the closest analog to eastern Maine. Adults survive 97–98 % a year, mature at 9–11 years and live more than 60. They hibernate on or in the bottom mud, under about 0.3 m of water at southern Ontario sites, and stayed submerged for at least 143 days in central Ontario. Nesting runs from late May to early July; Ontario nests lay a median 11 m from water, and Nova Scotia clutches averaged 8.6 eggs. Incubation takes 65–97 days; temperatures ≤ 26 °C give males and ≥ 29 °C females. Nest predation, mainly by raccoons and foxes, runs from about 17 % to over 90 %. One population tolerated 70 %, but 90 % would cause decline (all via COSEWIC 2018). In New Hampshire, 22 % of artificial nests were depredated or disturbed within a week (Marchand et al. 2002). Most northern hatchlings overwinter in the nest: in south-central New Hampshire only 7 of 42 hatchling observations were autumn emergences, and winter in the nest killed 26–100 % of hatchlings in three winters studied (Carroll & Ultsch 2007). Hatchlings survive −4 °C but die at −10.9 °C (Storey et al. 1988).

Table 3.8-2. Painted turtle densities (turtles per ha), from COSEWIC (2018) and the studies it cites.

The snapping turtle is common in Maine. It lays in June in sandy soil, including gravel road shoulders, up to 3 km from water (MDIFW n.d., snapping turtle page). Eggs hatch about 85 days later from clutches of 25–45 (an MDIFW biologist in the Sun Journal, via a search summary). Northern densities are about 1.5 adults per ha overall (Obbard 1983) and 1.5–2.4 in Algonquin Park (Brooks et al. 1988; both via Kynast n.d.). In New Hampshire, all 14 known hatchling emergences fell on 5–24 September (Carroll & Ultsch 2007). Adults survive 93–97 % a year, only 1–1.8 % of juveniles reach breeding age, and females first nest at about 19 years (Kynast n.d., a secondary review). Diet reports conflict. One summary gives about one-third game fish and one-third plants in 173 Michigan stomachs (Lagler 1939, via a search summary of an unreadable scan). Another gives about 65 % vegetation and mainly slow non-game fish (Kynast n.d.). Snapping turtles ate netted adult alewives in Downeast lakes (Willis 2006). The spotted turtle (state Threatened) occurs only in southern and central Maine, and Blanding's turtle (Endangered) only in York and Cumberland counties (MDIFW n.d., species pages). Wood turtle occurrence in the drainage is unconfirmed. iNaturalist holds 21 painted and 21 snapping turtle records within 40 km, none from the lakes (project query).

3.8.6 Frogs, salamanders and newts

Three summer-breeding frogs are tied to permanent lake water (Table 3.8-3). Green frogs rarely go more than 1 m from water except on rainy nights (Minton 1972, via VHS n.d.) and eat mostly terrestrial invertebrates (Ontario Nature n.d.). Their tadpoles overwinter once, and Maine adults hibernate from October to March (Hunter et al. 1999, via VHS n.d.). Bullfrogs eat more aquatic prey: in Michigan, 19–23 % Hemiptera, 12–18 % adult Odonata and 5–15 % frogs (Werner et al. 1995). They stay inactive until water nears 15 °C (Harding 1997), and in Maine they breed when air exceeds 20 °C (MDIFW n.d., bullfrog page). Bullfrogs hibernate in bottom mud (MDIFW n.d., bullfrog page); radio-tagged Nova Scotia frogs tolerated pond oxygen partial pressures below 20 Torr for more than 8 weeks (Friet & Pinder 1990, via VHS n.d.), but bullfrogs are not freeze-tolerant (via VHS n.d.). Their tadpoles are relatively unpalatable to fish (Werner & McPeek 1994, via VHS n.d.). The mink frog, at the southern edge of its range in Maine, lives in shallow, dense emergents (MDIFW n.d., mink frog page). Chytrid fungus occurred in 7 of 9 Maine frog species in 2000–02, at 14.6–25.7 % prevalence, with no die-offs (Longcore et al. 2007).

Table 3.8-3. The lake-breeding frogs of Maine. Values from MDIFW species pages and the Virginia Herpetological Society accounts (VHS n.d.) unless noted.

The vernal-pool breeders (wood frog, spotted and blue-spotted salamanders) migrate on warm rainy nights, above about 4–7 °C. Migration runs from mid-March in southern Maine to mid-May in the north, and fish make lakeshores "biological sinks" for spotted salamanders (Calhoun & deMaynadier 2001; MDIFW n.d., amphibian blog). The red-spotted newt, by contrast, lives in lakes as an adult, some active all winter. Fish largely avoid it for its skin toxin, probably tetrodotoxin (MDIFW n.d., eastern newt page; Marion & Hay 2011). iNaturalist records within 40 km of the lakes show where people have looked (Table 3.8-4). The northern leopard frog is the most-recorded amphibian or reptile. The mink frog has only 2 records within 40 km, though 263 lie north of 45.3° N. A northern two-lined salamander recorded west of Upper in 2017 is the expected brook salamander (project inference). The common water snake is probably absent, since its northernmost records lie about 50 km south (project query); a University of Maine honors thesis (Pawlicki 2017) found that climate, not lake pH or size, predicted its presence.

Table 3.8-4. iNaturalist records of amphibians and reptiles within 40 km of the lakes and in Washington County (project query of the iNaturalist API). Counts measure observer effort, not abundance.

3.8.7 Dragonflies, damselflies and other aquatic insects

The New Brunswick Museum holds Odonata specimens from both lakes (via GBIF; other insect orders were not searched). From Upper, on 28 July 2005, came Ischnura verticalis, Enallagma minusculum (a soft-water species), E. civile and Lestes vigilax. From Lower, on 22 August 1999, came Hagenius brevistylus, Sympetrum costiferum, S. obtrusum, S. vicinum, Argia fumipennis and Aeshna canadensis. Specimens collected in 2003–05 on Baskahegan Stream, the lakes' receiving water, include more than 20 species, seven of them clubtails. iNaturalist holds 89 odonate taxa within 50 km, and several rare river clubtails, one of them state Threatened, occur in the region's larger rivers (project queries). Adult flight seasons run from early May to mid-November (Table 3.8-5).

Table 3.8-5. Adult flight seasons of lake odonates and of Hexagenia in Maine, from weekly iNaturalist histograms (project analysis). Week 18 ≈ 30 April–6 May, week 21 ≈ 21–27 May, week 25 ≈ 18–24 June, week 30 ≈ 23–29 July, week 38 ≈ 17–23 September, week 46 ≈ 12–18 November.

No odonate larval density from a Maine lake was found. A global review of lentic studies gives 104 ± 55 larvae per m² (damselflies 124, dragonflies 35), a biomass of 87 mg/m² and a production of 748 mg m⁻² yr⁻¹ (Rivas-Torres & Cordero-Rivera 2024). Fish reduce odonate numbers (Bendell & McNicol 1995, relayed by search summaries). In a Spanish pond, most exuviae were on emergent stems 6–20 cm above the water (Cordero 1995, relayed by a search summary). On Vermont lakes, developed shore sites yielded 1.6 exuviae against 9.1 at reference sites (Merrell et al. 2009), and no exuviae were found on seawalls, beaches or lawns (Burnham, Howe & Merrell, slides). Odonate larvae are a principal food of small chain pickerel and, where crayfish are scarce, of smallmouth bass (Swinemar, Campbell & Reid 2024, abstract only; Feener & MacLeod 2020; Section 3.7).

The other aquatic insects near the lakes are known only from iNaturalist records within 60 km (project query). The burrowing mayfly Hexagenia limbata flies mainly from late June to late July in Maine records, and its pond hatch begins once surface water reaches 18–21 °C, with emergence near dusk (Bangor Daily News 2022, popular source). Lentic caddisflies (Ptilostomis, Banksiola, Limnephilus, Mystacides, Triaenodes) and riffle caddisflies (Hydropsyche, Cheumatopsyche, Chimarra) are recorded, and caddisfly records peak from late May to mid-August. Black flies peak from mid-April to early June. Maine has 163 known chironomid species (Maine Aquatic Biodiversity Project, Ch. 6), but no Maine chironomid emergence dates or Hexagenia densities were found.

Emergence carries lake production ashore. Across 49 whole-lake estimates, 0.30 ± 0.04 of insect production emerged (Vander Zanden & Gratton 2011). At Mývatn, 70 % of midge deposition fell within 100 m of shore (Dreyer et al. 2015). Emergent insects supply 25–100 % of the energy of riparian birds, bats and spiders (Baxter et al. 2005, abstract only). Aerial insectivores recorded near the lakes include eastern phoebe, alder flycatcher and tree swallow (65, 59 and 48 regional records; project query). Tree-swallow nestlings eat mostly Diptera, Hemiptera and Odonata (Twining et al. 2018). The regular bats of Aroostook County are the little brown, big brown, hoary, silver-haired and eastern red. White-nose syndrome, present since 2011, has caused declines of about 95 % (Bangor Daily News 2023, quoting MDIFW). Little brown bats forage along water edges; a reproductive female eats about 5.5 g of insects a night when pregnant and up to about 9.9 g at peak lactation (Kurta et al. 1989, via a secondary source). Fall-in insects and leaves are treated in Section 3.2.

3.8.8 The forest

The catchments above Upper's and Lower's outlets (about 66 and 77 km²) are 70–73 % forest by NLCD 2019. Upper's is 30.0 % deciduous, 32.3 % mixed and 10.7 % conifer, with 14.4 % woody wetland and 2.8 % developed (EPA StreamCat; Section 2). MDIFW's survey sheets nevertheless describe Upper as "mostly surrounded by spruce fir forest" and Lower as "surrounded by spruce fir forest" (MDIFW lake survey maps). The two accounts agree if the shores are coniferous and the uplands mixed, but no map of the shore band was found. About 40,000–61,000 ha of FSC-certified timberland around Danforth and Topsfield is managed by shelterwood cutting (Forest Stewards Guild / FSC US, via project notes).

Stand structure comes from a project analysis of USDA Forest Service Forest Inventory and Analysis (FIA) plots: the latest measurement of single-condition forest plots in 2021–25, summarized as plot medians rather than FIA's stratified estimates. The 105 plots within 40 km of the lakes describe a working forest with a median stand age of 55 years. By type group they are 48 % maple–beech–birch, 34 % spruce–fir and 11 % aspen–birch, with a median softwood share of basal area of 56 % (Table 3.8-6). Statewide, ecological reserves carry 28.5 m²/ha of basal area in trees ≥ 12.7 cm (28.0 on their non-harvested plots), against 17.4 on managed FIA plots (Kuehne et al. 2018). Maine averaged about 27,000 seedlings per ha in 2013, almost half of them under 0.3 m tall (McCaskill et al. 2016).

Table 3.8-6. Forest structure per hectare, median (interquartile range), FIA plots measured 2021–25 (project analysis). Trees ≥ 10 cm dbh; saplings 2.5–10 cm; seedlings < 2.5 cm dbh and ≥ 15 cm (conifers) or ≥ 30 cm (hardwoods) tall; snags ≥ 12.7 cm. "Eastern Maine" is Aroostook, Penobscot and Washington counties.

In mature eastern-Maine mixedwood, most stems ≥ 2.5 cm dbh are 5–15 m tall, and fewer than 5 per ha exceed 25 m (Table 3.8-7). Its canopy stems are 31 % red maple, 15 % balsam fir and 12 % yellow birch. Mature softwood canopies are 23 % fir, 17 % northern white-cedar and 15 % red maple. Balsam fir makes up 38–53 % of the 2–10 m subcanopy in softwood and mixedwood stands (project analysis of FIA data). Forest-grown crown widths come from Maine-fitted equations (Russell & Weiskittel 2012), with mean absolute errors of 0.58–1.52 m by species. At canopy size they are about 0.27 of tree height for fir and spruce and 0.4–0.45 for hemlock, yellow birch and beech. Open-grown (maximum) crowns from the same equations, a guide for lake edges, are 1.6–2 times the forest-grown widths in Table 3.8-8 (project analysis).

Table 3.8-7. Stems ≥ 2.5 cm dbh per hectare by total height in mature stands, eastern Maine FIA plots (project analysis).

Table 3.8-8. Median total height and forest-grown crown width (m) at two diameters, and uncompacted live crown ratio of trees ≥ 10 cm, Maine FIA 2021–25. Heights and crown ratios are from FIA trees; widths are from the Russell & Weiskittel (2012) equations (project analysis).

Under the canopy, mature Maine stands averaged 19 % shrub, 15 % fern, 22 % forb and 9 % graminoid cover, mostly below 0.6 m (project analysis of FIA vegetation data, 223 plots). Unharvested Penobscot Experimental Forest stands had only 2 % herb cover and 13.5 % bryophytes under 8.2 % canopy openness, against 41 % herbs in heavy cuts (project analysis of Olson et al. 2019 data). Bryophytes averaged 38 % cover in Maine red-spruce stands (Dibble et al. 1999), and Canada yew is heavily browsed by deer and moose (Sullivan 1993). Mature eastern-Maine softwood held a median of 74 snags ≥ 12.7 cm per ha, mixedwood 45 and hardwood 30, with only 1–3 per ha of 40 cm or more. Downed logs (≥ 7.6 cm) had a statewide median of 541 per ha (FIA 2006–10), and coarse woody debris (CWD) had a median of 28 m³/ha in mature eastern-Maine stands (project analysis of FIA data). Managed forest carries about half the snags of the ecological reserves and about half the downed wood of old growth (Table 3.8-9).

Table 3.8-9. Snags and coarse woody debris in managed and unmanaged Maine forest (Kuehne et al. 2018).

Maine lakeshores take three forms (project synthesis of MNAP and Vermont community descriptions, partly via search summaries; VT Fish & Wildlife n.d.). Exposed mineral shores carry a narrow sweetgale fringe and an ice-push berm. Sheltered peaty coves carry a sweetgale–leatherleaf–meadowsweet fen about 1 m tall, then alder 1–3 m tall, then cedar, spruce or red-maple swamp. On rocky shores the forest reaches the water. Lakeshore Beach is the commonest shore community on medium and large Maine lakes (MNAP n.d., Lakeshore Beach). Northern white-cedar persists around lakes because shores shelter it from fire and it resists ice, and Maine holds 88 % of the Northeast's cedar type (Boulfroy et al. 2012). Cedar is the most abundant seedling in mature eastern-Maine softwood, averaging 3,220 per ha (project analysis of FIA data). No measured width of the shrub band was found; a project estimate of 1–5 m on exposed shores and 5–50 m in coves is unsourced. At Hot Brook the angler reports sweet gale, speckled alder, northern white-cedar and bulrush, with sensitive fern on exposed brook bars (project field notes). NWI maps about 96 ha (237 acres) of forested swamp at Upper's south end (USFWS NWI, project query).

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