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The ecological consequences of winter in freshwater systems are an understudied but rapidly emerging research area. Here, we argue that winter periods of reduced temperature and light (and potentially oxygen and resources) could play an underappreciated role in mediating the coexistence of species. This may be especially true for temperate and subarctic lakes, where seasonal changes in the thermal environment might fundamentally structure species interactions. With climate change already shortening ice‐covered periods on temperate and polar lakes, consideration of how winter conditions shape biotic interactions is urgently needed. Using freshwater fishes in northern temperate lakes as a case study, we demonstrate how physiological trait differences (e.g. thermal preference, light sensitivity) drive differential behavioural responses to winter among competing species. Specifically, some species have a higher capacity for winter activity than others. Existing and new theory is presented to argue that such differential responses to winter can promote species coexistence. Importantly, if winter is a driver of niche differences that weaken competition between, relative to within species, then shrinking winter periods could threaten coexistence by tipping the scales in favour of certain sets of species over others. [ABSTRACT FROM AUTHOR]

Seasonal water temperature data from 388 large Canadian lakes (area ≥ 100 km2) were used to develop improved empirical tools for forecasting the impacts of climate change on the magnitude ( TP) and time of occurrence ( JP) of annual peak surface water temperatures. Analyses of remotely sensed open-water temperatures with sinusoidal models produced estimates of TP and JP predominately better than other models. Those estimates were analyzed for lake and climate patterns. Linear mixed effects regression produced a significant model of TP with fixed positive effects for mean July and annual air temperatures and lake perimeter, but negative effects with mean July and annual percent cloud cover, mean annual precipitation, range of monthly mean global clear sky radiation, area, and elevation. Subsets of the estimates with mean, maximum, or Secchi depth values produced similarly significant models with negative depth coefficients. JP was relatively invariant but small, significant lake and climate effects were detected. The best models identified in our analyses will be useful tools for forecasting how climate change will alter aspects of the limnetic seasonal water temperature cycle that strongly influences the species composition and productivity of their fisheries. [ABSTRACT FROM AUTHOR]

Nearshore waters are among the most biologically productive and anthropogenically developed in the North American Great Lakes. We examined site-to-site differences in the pattern of variation in the daily water temperatures obseived at water intakes located in nearshore regions of the Great Lakes. Data from 28 nearshore sites spread across all five lakes were analyzed. At each site, daily differences between nearshore and lake-wide surface water temperatures varied systematically with season, and these seasonal patterns varied systematically from site to site. We characterized these patterns using an index derived from quantile regression. Index values were related to site-specific factors such as depth, fetch and exposure. We broadened these empirical analyses to develop a tool for extending, to nearshore water temperatures, previously published projections of climate change impacts on lake-wide mean surface water temperatures. This tool provided projections of the possible impacts of increasing surface water temperatures on nearshore water temperatures under a climate change scenario for the Great Lakes region. Projections were generated for nearshore sites characterized by a range of depth and fetch values representative of those found throughout the Great Lakes. Projected impacts varied with site characteristics, with likely implications for biological activity and human use. [ABSTRACT FROM AUTHOR]

Abstract: Energy storage is a common adaptation of fish living in seasonal environments. For some species, the energy accumulated during the growing season, and stored primarily as lipids, is crucial to preventing starvation mortality over winter. Thus, in order to understand the adaptive responses of fish life history to climate, it is important to determine how energy should be allocated to storage and how it trades off with the other body components that contribute to fitness. In this paper, we extend previous life history theory to include an explicit representation of how the seasonal allocation of energy to storage acts as a constraint on fish growth. We show that a strategy that privileges allocation to structural mass in the first part of the growing season and switches to storage allocation later on, as observed empirically in several fish species, is the strategy that maximizes growth efficiency and hence is expected to be favored by natural selection. Stochastic simulations within this theoretical framework demonstrate that the relative performance of this switching strategy is robust to a wide range of fluctuations in growing season length, and to moderate short-term (i.e., daily) fluctuations in energy intake and/or expenditure within the growing season. We then integrate this switching strategy with a biphasic growth modeling framework to predict typical growth rates of walleye Sander vitreus, a cool water species, and lake trout Salvelinus namaycush, a cold water specialist, across a climatic gradient in North America. As predicted, growth rates increased linearly with the duration of the growing season. Regression line intercepts were negative, indicating that growth can only occur when growing season length exceeds a threshold necessary to produce storage for winter survival. The model also reveals important differences between species, showing that observed growth rates of lake trout are systematically higher than those of walleye in relatively colder lakes. This systematic difference is consistent with both (i) the expected superior capacity of lake trout to withstand harsh winter conditions, and (ii) some degree of counter gradient adaptation of lake trout growth capacity to the climatic gradient covered by our data. [Copyright &y& Elsevier]

The ability of coldwater species and populations to respond to the predicted temperature increases associated with climate change will largely depend on existing adaptive potential within and among populations. Southern inland populations of Lake TroutSalvelinus namaycushare broadly characterized by two ecotypes (small and large bodied) which differ in their trophic ecology, life history traits, and body size. Using common-garden experiments, we investigated population-specific differences in thermal performance (growth, temperature tolerance, and temperature preference) and whether the differences were consistent between ecotypes. We further explored the role of acclimation temperature on growth and thermal performance in two representative ecotypic populations. The evidence from this study indicated that the differences were population specific rather than ecotype specific. A strong inverse relationship between early growth rate and temperature preference suggests that the differences in early growth among Lake Trout populations are driven by adaptive variation in temperature preference. Acclimation temperature had a greater effect than source population on growth and temperature tolerance, although both significantly influenced temperature preferences. Small-bodied ecotypes were less tolerant of elevated temperatures and exhibited less within-population variation, potentially indicating their greater vulnerability to changing ecological conditions under climate change scenarios. Received September 13, 2011; accepted January 14, 2013 [ABSTRACT FROM PUBLISHER]

Lake trout (Salvelinus namaycush) exhibit substantial life history variation range-wide and at a local scale. This study addresses two hypotheses that have been proposed to account for this: (i) over the zoogeographic range, climatic conditions are associated with life history differences; and (ii) within smaller geographic regions, physical lake attributes are associated with life history differences. Multivariate statistics (Procrustean analysis and canonical correlation analysis) identified a strong, range-wide association between climate and life history variables. Colder climates were associated with slower prematuration growth, older age at maturity, and increased longevity. Winter conditions were also important; longer, warmer winters were associated with slower prematuration growth, smaller maximum sizes, and increased weight at a standard length of 425 mm. In southern populations, these general trends were further modified by physical lake attributes. High productivity lakes had lake trout with faster prematuration growth and larger maximum sizes; deeper lakes were associated with larger maximum sizes and later ages at maturity; and larger lakes were associated with slower prematuration growth, greater longevity, and larger maximum sizes. This study identifies abiotic variables that should be incorporated into existing lake trout management models, thus extending their applicability range-wide and permitting them to deal with possible impacts of climate change. [ABSTRACT FROM AUTHOR]

Abstract: Temperature influences the rates of many ecosystem processes. A number of recent studies have found evidence of systematic increases in Great Lakes surface water temperatures. Our study aims to construct empirical relationships between surface water temperatures and local air temperatures that can be used to estimate future water temperatures using future air temperatures generated by global climate models. Remotely sensed data were used to model lake-wide average surface water temperature patterns during the open-water period in Lakes Superior, Huron, Erie, and Ontario. Surface water temperatures typically exhibit linear warming through the spring, form a plateau in mid-summer and then exhibit linear cooling in fall. Lake-specific warming and cooling rates vary little from year to year while plateau values vary substantially across years. These findings were used to construct a set of lake-specific empirical models linking surface water temperatures to local air temperatures for the period 1995–2006. Hindcasted whole-lake water temperatures from these models compare favourably to independently collected offshore water temperatures for the period 1968–2002. Relationships linking offshore water temperatures to inshore water temperatures at specific sites are also described. Predictions of future climates generated by the Canadian Global Climate Model Version 2 (CGCM2) under two future greenhouse gas emission scenarios are used to scope future Great Lakes surface water temperatures: substantial increases are expected, along with increases in the duration of summer stratification. [Copyright &y& Elsevier]

Walleye (Sander vitreus) is a native fish species in North America, and its zoogeographic range covers several climatic zones. Using multivariate statistical approaches and published growth data, we explored the association between climatic conditions (frost frequency, precipitation, air temperature, solar radiation, and cloud cover) and growth of walleye from 89 populations in North America. We found significant concordance between climatic conditions and walleye growth; however, the pattern of concordance differed among populations that originated from geographical regions that were colonized from different glacial refugia. This suggests that contemporary differences in walleye growth patterns related to local climatic conditions may have been shaped by evolutionary divergence that occurred among refugia during the last glaciation. We suggest that caution should be taken when assessing possible effects of climate variation and climate change on the life history traits of different walleye and other fish populations, especially when such assessments potentially include several genetically distinct groups. Procrustes analysis was shown to be an effective tool for characterizing how a multivariate set of response variables change in response to generalized changes in a multivariate set of independent variables. [ABSTRACT FROM AUTHOR]

Predicted increases in water temperature in response to climate change will have large implications for aquatic ecosystems, such as altering thermal habitat and potential range expansion of fish species. Warmwater fish species, such as smallmouth bass, Micropterus dolomieu, may have access to additional favourable thermal habitat under increased surface-water temperatures, thereby shifting the northern limit of the distribution of the species further north in Canada and potentially negatively impacting native fish communities. We assembled a database of summer surface-water temperatures for over 13 000 lakes across Canada. The database consists of lakes with a variety of physical, chemical and biological properties. We used general linear models to develop a nation-wide maximum lake surface-water temperature model. The model was extended to predict surface-water temperatures suitable to smallmouth bass and under climate-change scenarios. Air temperature, latitude, longitude and sampling time were good predictors of present-day maximum surface-water temperature. We predicted lake surface-water temperatures for July 2100 using three climate-change scenarios. Water temperatures were predicted to increase by as much as 18 °C by 2100, with the greatest increase in northern Canada. Lakes with maximum surface-water temperatures suitable for smallmouth bass populations were spatially identified. Under several climate-change scenarios, we were able to identify lakes that will contain suitable thermal habitat and, therefore, are vulnerable to invasion by smallmouth bass in 2100. This included lakes in the Arctic that were predicted to have suitable thermal habitat by 2100. [ABSTRACT FROM AUTHOR]

Future changes to climate in the Great Lakes may have important consequences for fisheries. Evidence suggests that Great Lakes air and water temperatures have risen and the duration of ice cover has lessened during the past century. Global circulation models (GCMs) suggest future warming and increases in precipitation in the region. We present new evidence that water temperatures have risen in Lake Erie, particularly during summer and winter in the period 1965–2000. GCM forecasts coupled with physical models suggest lower annual runoff, less ice cover, and lower lake levels in the future, but the certainty of these forecasts is low. Assessment of the likely effects of climate change on fish stocks will require an integrative approach that considers several components of habitat rather than water temperature alone. We recommend using mechanistic models that couple habitat conditions to population demographics to explore integrated effects of climate-caused habitat change and illustrate this approach with a model for Lake Erie walleye (Sander vitreum). We show that the combined effect on walleye populations of plausible changes in temperature, river hydrology, lake levels, and light penetration can be quite different from that which would be expected based on consideration of only a single factor. [ABSTRACT FROM AUTHOR]

Natural resource decision makers are challenged to adapt management to a changing climate while balancing short-term management goals with long-term changes in aquatic systems. Adaptation will require developing resilient ecosystems and resilient management systems. Decision makers already have tools to develop or ensure resilient aquatic systems and fisheries such as managing harvest and riparian zones. Because fisheries management often interacts with multiple stakeholders, adaptation strategies involving fisheries managers and other partners focused on land use, policy, and human systems, coupled with long-term monitoring, are necessary for resilient systems. We show how agencies and organizations are adapting to a changing climate in Minnesota and Ontario lakes and Montana streams. We also present how the Florida Fish and Wildlife Commission created a management structure to develop adaptation strategies. These examples demonstrate how organizations and agencies can cope with climate change effects on fishes and fisheries through creating resilient management and ecological systems. [ABSTRACT FROM AUTHOR]