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Lake Winnipeg has undergone extensive changes in environmental conditions and fish community structure during recent decades. The presence of cyanobacteria and invasive species as well as eutrophication, flow regulation, fishing pressure, and climate change all have potential impacts on the native fish community. Since 2002, pelagic forage fish species and early life stages of large-bodied fish species in the pelagic zone in Lake Winnipeg (Manitoba, Canada) have been monitored. Catch data were used to study the temporal variation in species-specific occurrence and catch-per-unit-effort (CPUE) and to analyse the effects of lake condition on species occurrence and CPUE estimates. To account for the temporal variation observed for commonly caught prey species in Lake Winnipeg, we used a Bayesian approach, Integrated Nested Laplace Approximation (INLA), to compare the effects of environmental variables on occurrence and CPUE. The pelagic fish community composition varied among years, and CPUE declined by 2.2-fold between 2005–2008 and 2015–2018. Emerald shiner was the most dominate prey fish species but decreased in the catches since the early 2000's, while rainbow smelt have almost entirely disappeared from the catches in recent years. Overall, we observed a decrease in CPUE in four of six most caught, pelagic species. Important environmental variables explaining occurrence and CPUE of the six most caught species in the survey were temperature and Secchi, trawl, and water depths. The trawl survey serves as a valuable long-term monitoring tool to study trends in responses of both native and non-native species to ecosystem changes in Lake Winnipeg. [ABSTRACT FROM AUTHOR]

Abstract: To better understand patterns of temporal and spatial variation of fish assemblages in offshore waters of Lake Winnipeg (Manitoba, Canada), midwater trawl tows were conducted near lakewide monitoring stations from 2002 to 2008. Trawl samples collected during spring, summer, and fall from the south basin, channel, and north basin were used to study effects of season and geographic region within the lake on species biomass estimates. Within each region, effect of trawl depth was explored. Greatest biomass in trawl catches was from the south basin. Of the most commonly caught species, across all seasons, greater biomass of emerald shiner (Notropis atherinoides) and cisco (Coregonus artedi) were found in the south basin and the channel, compared to the north basin. Biomass of the non-native rainbow smelt (Osmerus mordax), by contrast, was greater in the north basin compared to the south basin or the channel. Yellow perch (Perca flavescens) and introduced white bass (Morone chrysops) biomass varied temporally and spatially, with greatest biomass captured in the summer in the south basin. Estimated biomass of walleye (Sander vitreus) was greatest in the south basin, followed by the channel, and the north basin. Patterns in species distribution in Lake Winnipeg probably are influenced by a combination of factors, including species interactions and differing temperature and light conditions in the lake. As no lakewide pelagic trawl studies have been reported for this lake, these data form a baseline against which effects of changes, such as lake trophic state or establishment of non-native species, can be assessed. [Copyright &y& Elsevier]

Patterns in abundance, growth, and condition of lake whitefish (Coregonus clupeaformis) from Lake Erie were compared with those from Lake Ontario. Discontinuous assessment data were available from 1972 to 2003 for each lake to describe abundance, growth, and condition, while a seasonally intensive field program was undertaken in 2003 to describe diet, energy density, and gonadosomatic index (GSI). Through time, abundance declined more in Lake Ontario than in Lake Erie. Length-at-age (growth) and condition both declined significantly in Lake Ontario but did not change in Lake Erie. Diet analysis revealed chironomids, dreissenid mussels and sphaeriids made up the bulk of lake whitefish diet in Lake Erie. Diet in Lake Ontario exhibited more seasonal variability with amphipods and gastropods comprising the bulk of the spring and fall diets, and dreissenid mussels dominating summer diets. Lake whitefish energy density (J/g wet mass) was significantly higher in Lake Erie than in Lake Ontario, increasing with body mass and strongly correlated with water content. Female gonadosomatic index was also significantly greater in Lake Erie than in Lake Ontario. Biological attributes of lake whitefish from Lake Erie did not change greatly from the late 1980s to 2003 while fish from Lake Ontario exhibited decreased size-at-age and condition likely due to decreased energy content of diets compared to predreissenid mussel conditions, and possibly lower availability of benthic prey compared to Lake Erie. [ABSTRACT FROM AUTHOR]