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At least 901 records · Page 50Linked to original sources
USGS2013

Distribution and exploitation of Nile perch Lates niloticus in relation to stratification in Lake Victoria, East Africa

Stratification restricts habitable areas forcing fish to balance between favourable temperature and minimum dissolved oxygen requirements. Acoustic surveys conducted during the stratified and isothermal periods on tropical Lake Victoria indicated that stratification of temperature and dissolved oxygen (DO) affected vertical distribution of Nile perch. There was higher mean temperature (25.6 ± 0.5 °C) and lower DO (6.4 ± 1.8 mg/l) during stratified period compared to the isothermal period (mean temperature 24.9 ± 0.3 °C; mean DO 7.3 ± 0.6 mg/l). Higher mean densities of Nile perch were recorded in the coastal (0.44 ± 0.03) and deep (0.27 ± 0.02 g/m 3 ) strata during the stratified compared to the isothermal season (coastal: 0.24 ± 0.01; deep: 0.12 ± 0.02 g/m 3 ). In addition, Nile perch density in the upper 0–40 m depth layers in the coastal and deep strata increased by over 50% from the isothermal to the stratified season. Daily landings from 65 motorised fishing boats between October 2008 and September 2010 show higher mean catch (26.29 ± 0.17 kg/boat/day) during stratified compared to the isothermal (23.59 ± 0.15) season. Thermal stratification apparently compresses the habitat available to Nile perch and can potentially result in higher exploitation. Managers should evaluate the potential benefits of instituting closed seasons during the stratified period, and stock assessment models should take into account the seasonal niche compression.

Journal of Great Lakes Research↗
USGS2013

Sensitivity of fish density estimates to standard analytical procedures applied to Great Lakes hydroacoustic data

Standardized methods of data collection and analysis ensure quality and facilitate comparisons among systems. We evaluated the importance of three recommendations from the Standard Operating Procedure for hydroacoustics in the Laurentian Great Lakes (GLSOP) on density estimates of target species: noise subtraction; setting volume backscattering strength (S v ) thresholds from user-defined minimum target strength (TS) of interest (TS-based S v threshold); and calculations of an index for multiple targets (N v index) to identify and remove biased TS values. Eliminating noise had the predictable effect of decreasing density estimates in most lakes. Using the TS-based Sv threshold decreased fish densities in the middle and lower layers in the deepest lakes with abundant invertebrates (e.g., Mysis diluviana). Correcting for biased in situ TS increased measured density up to 86% in the shallower lakes, which had the highest fish densities. The current recommendations by the GLSOP significantly influence acoustic density estimates, but the degree of importance is lake dependent. Applying GLSOP recommendations, whether in the Laurentian Great Lakes or elsewhere, will improve our ability to compare results among lakes. We recommend further development of standards, including minimum TS and analytical cell size, for reducing the effect of biased in situ TS on density estimates.

Great Lakes↗
USGS2015

Validation of a spatial model used to locate fish spawning reef construction sites in the St. Clair–Detroit River system

Lake sturgeon ( Acipenser fulvescens ) populations have suffered precipitous declines in the St. Clair–Detroit River system, following the removal of gravel spawning substrates and overfishing in the late 1800s to mid-1900s. To assist the remediation of lake sturgeon spawning habitat, three hydrodynamic models were integrated into a spatial model to identify areas in two large rivers, where water velocities were appropriate for the restoration of lake sturgeon spawning habitat. Here we use water velocity data collected with an acoustic Doppler current profiler (ADCP) to assess the ability of the spatial model and its sub-models to correctly identify areas where water velocities were deemed suitable for restoration of fish spawning habitat. ArcMap 10.1 was used to create raster grids of water velocity data from model estimates and ADCP measurements which were compared to determine the percentage of cells similarly classified as unsuitable, suitable, or ideal for fish spawning habitat remediation. The spatial model categorized 65% of the raster cells the same as depth-averaged water velocity measurements from the ADCP and 72% of the raster cells the same as surface water velocity measurements from the ADCP. Sub-models focused on depth-averaged velocities categorized the greatest percentage of cells similar to ADCP measurements where 74% and 76% of cells were the same as depth-averaged water velocity measurements. Our results indicate that integrating depth-averaged and surface water velocity hydrodynamic models may have biased the spatial model and overestimated suitable spawning habitat. A model solely integrating depth-averaged velocity models could improve identification of areas suitable for restoration of fish spawning habitat.

Michigan↗
USGS2016

Entrainment, retention, and transport of freely swimming fish in junction gaps between commercial barges operating on the Illinois Waterway

Large Electric Dispersal Barriers were constructed in the Chicago Sanitary and Ship Canal (CSSC) to prevent the transfer of invasive fish species between the Mississippi River Basin and the Great Lakes Basin while simultaneously allowing the passage of commercial barge traffic. We investigated the potential for entrainment, retention, and transport of freely swimming fish within large gaps (> 50 m 3 ) created at junction points between barges. Modified mark and capture trials were employed to assess fish entrainment, retention, and transport by barge tows. A multi-beam sonar system enabled estimation of fish abundance within barge junction gaps. Barges were also instrumented with acoustic Doppler velocity meters to map the velocity distribution in the water surrounding the barge and in the gap formed at the junction of two barges. Results indicate that the water inside the gap can move upstream with a barge tow at speeds near the barge tow travel speed. Water within 1 m to the side of the barge junction gaps was observed to move upstream with the barge tow. Observed transverse and vertical water velocities suggest pathways by which fish may potentially be entrained into barge junction gaps. Results of mark and capture trials provide direct evidence that small fish can become entrained by barges, retained within junction gaps, and transported over distances of at least 15.5 km. Fish entrained within the barge junction gap were retained in that space as the barge tow transited through locks and the Electric Dispersal Barriers, which would be expected to impede fish movement upstream.

Illinois↗
USGS2016

Telemetry narrows the search for sea lamprey spawning locations in the St. Clair-Detroit River System

Adult sea lamprey ( Petromyzon marinus ) abundance in Lake Erie has remained above targets set by fishery managers since 2005, possibly due to increased recruitment in the St. Clair-Detroit River System (SCDRS). Sea lamprey recruitment in the SCDRS poses an enormous challenge to sea lamprey control and assessment in Lake Erie because the SCDRS contains no dams to facilitate capture and discharge is at least an order of magnitude larger in the SCDRS than most other sea lamprey-producing tributaries in the Great Lakes. As a first step toward understanding population size, spatial distribution, and spawning habitat of adult sea lampreys in the SCDRS, we used acoustic telemetry to determine where sea lampreys ceased migration (due to spawning, death, or both) among major regions of the SCDRS. All tagged sea lampreys released in the lower Detroit River ( N = 27) moved upstream through the Detroit River and entered Lake St. Clair. After entering Lake St. Clair, sea lampreys entered the St. Clair River ( N = 22), Thames River ( N = 1), or were not detected again ( N = 4). Many sea lampreys (10 of 27) were last observed moving downstream (“fallback”) but we were unable to determine if those movements occurred before or after spawning, or while sea lampreys were dead or alive. Regardless of whether estimates of locations where sea lampreys ceased migration were based on the most upstream region occupied or final region occupied, most sea lampreys ceased migration in the St. Clair River or Lake St. Clair. Results suggest that spawning and rearing in the St. Clair River could be an important determinant of sea lamprey recruitment in the SCDRS and may direct future assessment and control activities in that system.

Michigan, Ontario↗
USGS2017

Movement patterns and spatial segregation of two populations of lake trout Salvelinus namaycush in Lake Huron

Movement ecology is an important component of life history and population dynamics, and consequently its understanding can inform successful fishery management decision-making. While lake trout populations in Lake Huron have shown signs of recovery from near extinction in recent years, knowledge of their movement behavior remains incomplete. We used acoustic telemetry to describe and compare movement patterns of two Lake Huron lake trout populations: Drummond Island and Thunder Bay. Both populations showed high spawning site fidelity, with no evidence of co-mingling during non-spawning season. Detections between spawning periods were mainly limited to receivers within 100 km of spawning locations, and suggested that the two populations likely remained segregated throughout the year. Drummond Island fish, which spawn inside the Drummond Island Refuge, primarily dispersed east into Canadian waters of Lake Huron, with 79–92% of fish being detected annually on receivers outside the refuge. In contrast, Thunder Bay fish tended to disperse south towards Saginaw Bay. Large proportions (i.e., > 80%) of both populations were available to fisheries outside the management zone containing their spawning location. Thunder Bay fish moved relatively quickly to overwinter habitat after spawning, and tended to repeat the same post-spawning movement behavior each year. The consistent, predictable movement of both populations across management zones highlights the importance of understanding population dynamics to effective management of Lake Huron lake trout.

Journal of Great Lakes Research↗
USGS2021

Telemetry evaluation of carbon dioxide as a behavioral deterrent for invasive carps

Carbon dioxide (CO 2 ) mixed into water is being explored as a possible management strategy to deter the upstream movements of invasive carps through navigation locks and other migratory pinch-points. This study used two-dimensional acoustic telemetry to assess the effectiveness of dissolved CO 2 as a chemosensory deterrent to two carp species in a large U-shaped pond. Free-swimming movements of telemetered bighead carp ( Hypophthalmichthys nobilis ) and grass carp ( Ctenopharyngodon idella ) were documented 24 h before treatment and 24 h during treatments at 60, 121 and 213 mg/L CO 2 (mean concentrations in pond water). Several behavioral endpoints were then quantified and compared to evaluate deterrence efficacy. In general, results showed that both carp species responded similarly to CO 2 treatments. Carps consistently relocated into areas away from the injection site and made fewer attempts to re-enter CO 2 treated areas. On average, CO 2 treatments reduced mid-line crosses between untreated and treated sides of the pond by 58% at 121 mg/L CO 2 and 78% at 213 mg/L CO 2 relative to normal swimming movements recorded before treatment. Fish swim speeds increased significantly when inside the CO 2 plume during treatments during 213 mg/L CO 2 trials relative to swim speeds outside the plume, possibly indicative of active searching and avoidance responses. Overall, this study found that CO 2 altered the behavior of bighead carp and grass carp. Natural resource agencies could consider the CO 2 concentrations identified in this study to inform future applications to deter invasive carps from locations where they are at-risk to move upstream.

Journal of Great Lakes Research↗
USGS2021

Evidence of successful river spawning by lake trout (Salvelinus namaycush) in the lower Niagara River, Lake Ontario

Restoration of a wild-produced lake trout Salvelinus namaycush population in Lake Ontario has not been successful despite the adult population often meeting or exceeding restoration targets. Lack of high-quality spawning habitat in Lake Ontario is suggested as one impediment to recruitment of wild lake trout, although the quantity and location of spawning habitat is poorly understood. If high-quality spawning habitat is limited in Lake Ontario, lake trout may be using uncommon spawning locations such as rivers. Anecdotal angler accounts point to the Niagara River as a lake trout spawning location. To better understand the potential of the Niagara River as a spawning location, egg and juvenile fish collections were conducted 12–14 river kilometers from the mouth of the Niagara River from 2010 to 2012; and mature female lake trout with surgically implanted acoustic tags were monitored from 2015 to 2019. Genetic analyses confirmed 60% of collected eggs and 93% of collected post-hatch juvenile fish in the Niagara River were lake trout. Tagged female lake trout returned to the Niagara River over consecutive years during the spawning season. The short duration of lake trout presence in the river (mean = 56 days/year) suggests female lake trout use the Niagara River primarily for spawning. Diversity in spawning locations may provide lake trout population’s resilience against environmental variability through a portfolio effect. Improved identification of riverine spawning locations, including their overall contribution to wild recruitment, may be a useful tool for managers to restore a wild-produced population of lake trout in Lake Ontario.

New York, Ontario↗
USGS2022

Multi-run migratory behavior of adult male lake sturgeon in a short river

Lake sturgeon ( Acipenser fulvescens ) can migrate long distances to spawn, but many populations currently spawn in systems where the length of accessible riverine migratory habitat has been greatly reduced by dam construction. With the increased prevalence of shortened rivers, focusing on migratory dynamics in short rivers (<30 km) is beneficial to understanding the migratory needs of lake sturgeon populations. Here we document male lake sturgeon movements during the spawning period in the Winooski River, Vermont, USA; a river with only 17 km to the first natural upstream barrier. Male lake sturgeon were acoustically tagged (n = 25, 1215–1470 mm TL) and tracked using five to nine stationary receivers from 2017 to 2019. River discharge, temperature, the lagged effect of temperature (3-day), and time of day were significant factors describing upstream movements of tagged fish. Migrating male lake sturgeon (n = 10 in 2017, n = 18 in 2018, and n = 17 in 2019) displayed general movement patterns during the spawning period that included a single run upstream to the spawning site (60%), upstream and downstream movements throughout the river during the season (20%), or multiple runs made up the entire length of the spawning tributary to the spawning site (20%). No multi-run males were observed during 2018 when discharge was less flashy (i.e., fewer steep increases and declines in discharge) than in 2017 and 2019. These results suggest that the prevalence of multi-run spawning behavior of male lake sturgeon is related to flow conditions.

Vermont↗
USGS2022

Results of the collaborative Lake Ontario bloater restoration stocking and assessment, 2012–2020

Bloater, Coregonus hoyi , are deepwater planktivores native to the Laurentian Great Lakes and Lake Nipigon. Interpretations of commercial fishery time series suggest they were common in Lake Ontario through the early 1900s but by the 1950s were no longer captured by commercial fishers. Annual bottom trawl surveys that began in 1978 and sampled extensively across putative bloater habitat only yielded one individual (1983), suggesting that the species had been locally extirpated. In 2012, a multiagency restoration program stocked bloater into Lake Ontario from gametes collected in Lake Michigan. From 2012 to 2020, 1,028,191 bloater were stocked into Lake Ontario. Bottom trawl surveys first detected stocked fish in 2015, and through 2020 ten bloater have been caught (total length mean = 129 mm, s.d. = 44 mm, range: 96–240 mm). Hatchery applied marks and genetic analyses confirmed the species identification and identified stocking location for some individuals. Trawl capture locations and acoustic telemetry suggested that stocked fish dispersed throughout the main lake within months or sooner, and the depth distribution of recaptured bloater was similar to historic distributions in Lake Ontario and other Great Lakes. Predicted bloater trawl catches, based on modeled population abundance and trawl survey efficiency, were similar to observed catches, suggesting that post-stocking survival is less than 20% and contemporary bottom trawl surveys can quantify bloater abundance at low densities and track restoration.

Lake Ontario↗
USGS2023

Does hatchery rearing of lake trout affect their reproductive behavior in the wild?

Stocking of hatchery-reared fishes has been used with variable success as a management action to promote the recovery of populations and species. The practice has been controversial for several reasons, including uncertainty about whether the hatchery rearing experience may affect reproduction after release. Fine-scale acoustic telemetry was used during three spawning seasons to test whether hatchery rearing affects the reproductive behavior of lake trout using a spawning shoal complex in northern Lake Huron. Within sex, wild- and hatchery-reared fish behaved similarly, but significant behavioral differences occurred between sexes. Lake trout of both sexes moved synchronously onto the spawning shoals at the completion of autumn thermal turnover and occupied the same spawning sites (confirmed visually by presence of fertilized eggs) on the shoals. Male lake trout tended to congregate directly on spawning sites, with duration of occupancy varying greatly among years. Female lake trout spent less time on spawning shoals than males and congregated less at spawning sites on shoals. Most fish visited multiple spawning sites among shoals per season, with many making multiple transits among individual spawning sites. We found no evidence to support the hypothesis that hatchery rearing impairs spawning behavior of lake trout and, therefore, conclude that behavior deficiencies on the spawning ground are likely not an impediment to rehabilitation of lake trout in northern Lake Huron. Our study narrows the field of possible impediments to lake trout rehabilitation in the Great Lakes and provides insights that expand the conceptual model of lake trout spawning behavior.

Michigan↗
USGS2023

Habitat selection by lake trout at reefs near Drummond Island, Lake Huron: An evaluation of physical characteristics used for spawning

Continued dependence on stocking of hatchery-reared lake trout, Salvelinus namaycush , in the Laurentian Great Lakes indicates recruitment bottlenecks still exist between spawning and the juvenile life stage (age-1). Possible impediments include poor habitat quality and an inability of hatchery-origin adults to select substrates that support successful incubation. Understanding of characteristics of suitable lake trout spawning habitat is limited but has centered on the cobble-contour framework, which identifies sloped reefs with cobble substrate and deep interstices to entrain eggs as spawning habitat. A novel sampling design based on acoustic-telemetry detections was used to evaluate relative importance of cobble-contour habitat characteristics (substrate size, homogeneity, interstitial depth, and slope) for predicting egg presence on two spawning reefs in northern Lake Huron. Fixed effect logistic regression models were used to relate egg presence to all possible combinations of measured physical characteristics. Physical characteristics of sites with naturally spawned eggs present varied, and no single best model predicted egg presence. Model selection and multi-model inference revealed slope to be the only informative predictor. Substrate size, homogeneity, and interstitial depth were not important. Embryo survival-to-hatch was also compared among sampling sites using in situ habitat bioassays seeded with hatchery fertilized embryos. No difference in embryo survival was observed between sites where naturally spawned eggs were present vs. absent. Over half of sites evaluated exceeded 75% survival. Naturally spawned eggs were observed at 25 of 57 sites. We suspect other characteristics such as interstitial flow could be helpful for predicting selection of lake trout spawning habitats.

Michigan↗
USGS2024

On the survival and habitat use of hatchery-reared cisco (Coregonus artedi) in Lake Erie

Cisco ( Coregonus artedi ) have been extirpated from Lake Erie in North America since the 1960s, but they once supported one of the largest Laurentian Great Lakes fisheries. Numerous potential impediments to rehabilitation have been identified, including summer habitat refugia and predation. We used acoustic telemetry to investigate the thermal habitat use and survival of hatchery-reared adult cisco in Lake Erie. Fish were experimentally released (n = 50 per site) offshore at Dunkirk, New York, in the eastern basin and Huron, Ohio, in the central basin. Cisco in both basins found suitable summer oxythermal habitat in the metalimnion, suggesting that coldwater habitat availability is likely not an impediment for reestablishment. However, track end dates or predation dates were distributed across only four months with the last detection at 155 days. Predation sensors combined with temperature values during digestion indicated different potential predators: lake trout ( Salvelinus namaycush ) for the Dunkirk group and walleye ( Sander vitreus ) for the Huron group. Additionally, digestion temperatures of two tags indicated bird predation was also important, likely underestimated and suggested substantial use of the epilimnion by tagged fish. The results highlight the need for additional studies to address stocking optimization questions in support of future reintroduction experiments and related cisco conservation efforts.

Lake Erie↗
USGS2025

Grass carp (Ctenopharyngodon idella) movement states and backwater use can inform removal efforts

Expansion of grass carp ( Ctenopharyngodon idella ) within the Laurentian Great Lakes poses significant ecological and economic risks. Suppression efforts to remove grass carp have increased to curtail population growth, but capture efficiency remains low. One management challenge is the lack of understanding how this invasive species is using its novel habitats in the Great Lakes. This study aimed to identify spatiotemporal patterns in grass carp behavior and backwater use that could be exploited by management efforts, including removal. We used acoustic telemetry to examine when grass carp occurred in areas vulnerable to removal by boat electrofishing in the Sandusky River, Ohio, USA. Hidden Markov models were used to categorize behavioral states and evaluate their relationships with environmental factors. Best performing 2-state and 3-state hidden Markov models included proximity to backwater as a factor in state-dependent step length and transition probability between states, with a higher probability of being in less mobile states during the middle of the day and in backwaters. For the 2-state model, this less mobile state was also more common during warmer temperatures. Distinct diel patterns and backwater use identified in this study provide critical insights for improving management. Model results suggest that current removal efforts, focused primarily on the mainstem of the river, may benefit from adjustments in both timing and removal gear. The findings raise further questions about unobserved behaviors contributing to state assignment and sufficiently flexible adaptive management strategies to account for individual variation in grass carp behavior.

Ohio↗
USGS2025

Movement characterizations of stocked juvenile lake sturgeon (Acipenser fulvescens) within the Genesee River, NY

Knowledge of the movements of post-stocked juvenile lake sturgeon ( Acipenser fulvescens ) within and beyond the Genesee River of New York is limited. Describing lake sturgeon post-stocking movements could further the understanding of population structure and the delineation of nursery habitat. This project aimed to characterize the movements of juvenile sturgeon by tagging and tracking 69 age-0 + and 30 sub-adult lake sturgeon with acoustic transmitters from 2019 to 2021. Habitat use was disproportionate between the two life stages of juvenile sturgeon; age-0 + lake sturgeon primarily inhabited the upper reaches of the Genesee River, while sub-adults primarily utilized the lower dredged reaches of the Genesee River and the embayment outside of the river. A lower proportion of age-0 + lake sturgeon left the Genesee River relative to sub-adults, with seven sub-adult sturgeon (23.3 % of all tagged) moving to new habitats over 100 km away. Water temperature, discharge, and dissolved oxygen concentrations best predicted lake sturgeon movement within the river. These results indicate that the Genesee River is serving as a nursery habitat for juvenile lake sturgeon and that connectivity exists among the river, nearshore Lake Ontario habitats, and other tributaries. Such information is important when considering that management efforts for this species are commonly uniform across a system, while our results suggest a broader metapopulation framework may be relevant.

New York↗
USGS2025

Emigration probabilities and survival estimates of stocked juvenile lake sturgeon (Acipenser fulvescens) within the Genesee River, NY

Knowledge of juvenile lake sturgeon ( Acipenser fulvescens ) survival is important both to understanding changes in population abundance and for assessing the efficacy of management practices like stocking. High mortality rates of juvenile fish are partially mitigated by stocking hatchery-raised individuals; however, survival of post-stocked lake sturgeon remains lower compared to survival at older life stages. In this study, acoustic telemetry data from 69 age-0+ (weight: = 29 g, range = 2–41 g; length: = 198 mm, range = 176–223 mm) and 30 sub-adults (weight: = 2144 g, range = 1100–7020 g; length: = 751 mm, range = 605–1020 mm) tagged in the fall of 2019 and 2020 were utilized to construct a multi-state model used to estimate both survival and spatial transitions between the Genesee River and Lake Ontario. Sub-adults (approximate ages: 4–7 years) had estimated survival rates exceeding 88 % in both the Genesee River and Lake Ontario. Age-0+ lake sturgeon displayed much lower survival rates that ranged between 31 % (Lake Ontario) and 77 % (Genesee River). Both age-0+ and sub-adults lake sturgeon were most likely to leave the Genesee River in the fall and winter months, while being most likely to return in the spring and summer months. The approach used in this study to estimate survival is hypothesized to have led to higher survival estimates than traditional Capture-Mark-Recapture (CMR) derived estimates as a result of accounting for emigration from the Genesee River.

New York↗
USGS2026

Lake trout colonization of artificial reefs: Who’s interested, and how long does it take?

Restoring self-sustaining lake trout ( Salvelinus namaycush ) populations has been a major management objective for decades across the species’ native range. Reproduction has been observed but recruitment has been limited in many areas of the Laurentian Great Lakes. Reef restoration and construction have been proposed to increase recruitment, leading to the construction of experimental spawning reefs in Thunder Bay, Lake Huron, during 2009–2010. Research shortly after reef construction demonstrated lake trout quickly colonized those reefs during spawning. We revisited this site after 10 years to evaluate lake trout encounter rate and residency on each reef over time and relative to an adjacent historical, anthropogenic reef complex using fine-scale acoustic telemetry. Encounter frequency increased at most experimental reefs since reef construction, but changes in residency were dependent on lake trout origin (hatchery or wild). Hatchery-produced fish increased their residency on the experimental reefs and spent more time on these reefs collectively than the historical reef; wild lake trout continued to primarily use the historical reef. We expected younger wild fish to have increased residency on the experimental reefs assuming these individuals could have originated from those reefs and were therefore more likely to return to them; however, residency on experimental reefs remained low (< 50%) for these fish. These results indicate that reef construction provided additional habitat used by spawning lake trout, but wild individuals continue to prefer older habitat including naive wild fish born after reef construction.

Michigan↗
USGS2026

Thermal habitat use of lake trout in Lake Erie

Understanding the thermal habitat use of fish populations is vital for effective rehabilitation or management, particularly in the face of climate change, given limited thermal tolerances of some species. In Lake Erie, lake trout ( Salvelinus namaycush ) rehabilitation efforts by means of stocking have been ongoing for four decades. However, high water temperatures and lengthening periods of stratification may be hindering reestablishment efforts by contributing to unfavorable conditions for spawning and natural recruitment. We used acoustic telemetry to quantify weekly temperature occupancy of adult lake trout in Lake Erie and evaluated whether temperature occupancy differed relative to fish total length and sex. We found that lake trout occupied water temperatures similar to temperatures occupied by other Great Lakes lake trout populations during summer stratification. During fall, lake trout in Lake Erie occupied warmer temperatures than Lake Huron populations but similar temperatures to Lake Ontario populations. Occupied temperatures decreased with increasing body size during a 7-week period of mid- to late-summer stratification, but not during early summer or fall. Male and female lake trout did not differ in weekly temperature occupancy during any season. These findings reveal similarities with successfully reproducing populations, which suggest that adult temperature occupancy is unlikely to be a major impediment to natural recruitment in Lake Erie.

Lake Erie↗