Kevin E. Wehrly

Field-Based Estimates of Thermal Tolerance Limits for Trout: Incorporating Exposure Time and Temperature Fluctuation

Abstract We used temperature and fish data from streams across Michigan and Wisconsin to estimate upper thermal tolerance limits for brook trout Salvelinus fontinalis and brown trout Salmo trutta. Tolerance limits were estimated for the maximum daily mean temperature (MEANT), maximum daily maximum temperature (MAXT), and maximum daily temperature range (RNGT) at exposure lengths of 1, 3, 7, 14, 21, 28, 35, 42, 49, 56, and 63 d. We found no difference in the upper thermal tolerance limit for brook and brown trout. For time periods of 1–14 d, the upper temperatures tolerated by trout decreased rapidly from 25.3°C to 22.5°C for MEANT and from 27.6°C to 24.6°C for MAXT. For time periods from 21 to 63 d, the upper temperatures tolerated by trout declined more gradually from 22.1°C to 21.0°C for MEANT and from 24.2°C to 22.9°C for MAXT. The 7-d upper tolerance limit was 23.3°C for MEANT and 25.4°C for MAXT. The maximum RNGT tolerated by trout varied as a function of mean temperature and length of exposure. Our ...

Defining and Characterizing Coolwater Streams and Their Fish Assemblages in Michigan and Wisconsin, USA

Abstract Coolwater streams, which are intermediate in character between coldwater “trout” streams and more diverse warmwater streams, occur widely in temperate regions but are poorly understood. We used modeled water temperature data and fish assemblage samples from 371 stream sites in Michigan and Wisconsin to define, describe, and map coolwater streams and their fish assemblages. We defined coolwater streams as ones having summer water temperatures suitable for both coldwater and warmwater species and used the observed distributions of the 99 fish species at our sites to identify coolwater thermal boundaries. Coolwater streams had June-through-August mean water temperatures of 17.0–20.5°C, July mean temperatures of 17.5–21.0°C, and maximum daily mean temperatures of 20.7–24.6°C. We delineated two subclasses of coolwater streams: “cold transition” (having July mean water temperatures of 17.5–19.5°C) and “warm transition” (having July mean temperatures of 19.5–21.0°C). Fish assemblages in coolwater stream...

A Multimetric Assessment of Stream Condition in the Northern Lakes and Forests Ecoregion Using Spatially Explicit Statistical Modeling and Regional Normalization

Abstract We sampled fish communities, water temperature, water chemistry, physical habitat, and catchment characteristics for 94 stream sites selected randomly throughout the Northern Lakes and Forests ecoregion and used those data to explicitly model reference conditions and assess ecological stream condition at each site via a regional normalization framework. The streams we sampled were first order through fourth order, and the catchments ranged from 0.9 to 458 km2. We developed multiple linear regression (MLR) models that predicted fish community metrics, water chemistry characteristics, and local physical habitat from catchment characteristics; we used these models to compare existing conditions with the conditions that would be expected based on the regression models. Our results indicated that the fish communities were relatively unimpaired because the catchment variables associated with human-induced land use change were important in only 1 of the 10 fish metric models. Agricultural land use was a...

A Landscape-Based Classification of Fish Assemblages in Sampled and Unsampled Lakes

Abstract We related fish species patterns and landscape-scale environmental data from 216 Michigan lakes to identify repeatable types of fish assemblages, identify environmental factors related to assemblage types, and classify fish assemblages in unsampled lakes. Multivariate regression tree modeling of fish species abundances identified six assemblage types that were explained by degree-days during the ice-free period, lake surface area, and mean lake surface temperature. Warmwater species dominated southern lakes, while coolwater and coldwater species had higher abundances in northern lakes. Coolwater species were present in large southern lakes, whereas warmwater species were excluded from northern lakes that had low mean surface temperatures or low degree-days. These results suggest that patterns of lake fish assemblages are shaped by differences in climate as well as lake-specific differences in surface temperature regimes and in vertical availability of coldwater and coolwater habitats. Because we ...

Assessing local and landscape patterns of residential shoreline development in Michigan lakes

Abstract We evaluated relationships between residential development intensity and littoral zone habitat and disturbance characteristics in 332 Michigan lakes 4 ha and larger. We also developed a landscape-based model to estimate lakeshore status in more than 6500 unsampled lakes. Residential development had strong negative effects on large woody debris and strong positive effects on shoreline armoring and docks at both local and whole-lake scales. Lakes having greater cumulative residential development showed greater littoral zone impacts at local scales. Littoral habitats were more heavily impacted in larger lakes and in lakes in southern Michigan. Results of our predictive modeling identified the following as important predictors of residential shoreline development: the amount of urban land use, public ownership, and wetlands in a 100 m buffer around a lake as well as distance to major population centers. Statewide estimates of shoreline development showed that in southern Michigan only 8% of lakes were undeveloped and that 23% had low and 69% had high development intensity. In contrast, 30% of northern Michigan lakes were undeveloped and 48% had low and only 22% had high development intensity. Land planning policy and lake management should consider cumulative effects of lakeshore development as well as the effects of region and lake type. Our study provides the basis for developing regional strategies to protect, restore, and manage lake ecosystems.

Assessment of dam effects on streams and fish assemblages of the conterminous USA

Despite the prevalence of damming as a global disturbance to river habitats, detailed reach-based assessments of the ecological effects of dams are lacking, particularly across large spatial extents. Using data from nearly 50,000 large dams, we assessed stream network fragmentation and flow alteration by large dams for streams of the conterminous USA. We developed 21 dam metrics characterizing a diversity of dam influences operating at both localized (e.g., distances-to-dams) and landscape scales (e.g., cumulative reservoir storage throughout stream networks) for every stream reach in the study region. We further evaluated how dams have affected stream fish assemblages within large ecoregions using more than 37,000 stream fish samples. Streams have been severely fragmented by large dams, with the number of stream segments increasing by 801% compared to free-flowing streams in the absence of dams and a staggering 79% of stream length is disconnected from their outlet (i.e., oceans and Great Lakes). Flow alteration metrics demonstrate a landscape-scale disturbance of dams, resulting in total upstream reservoir storage volumes exceeding estimated annual discharge volumes of many of the nations largest rivers. Further, we show large-scale changes in fish assemblages with dams. Species adapted to lentic habitats increase with dams across the conterminous USA, while rheophils, lithophils, and intolerant fishes decrease with dams. Overall, fragmentation and flow alteration by dams have affected fish assemblages as much or more than other anthropogenic stressors, with dam effects generally increasing with stream size. Dam-induced stream fragmentation and flow alteration are critical natural resource issues. This study emphasizes the importance of considering dams as a landscape-scale disturbance to river habitats along with the need to assess differential effects that dams may have on river habitats and the fishes they support. Together, these insights are essential for more effective conservation of stream resources and biotic communities globally.

Advancement of Geospatial Capability by NRiSD and GLAHF in Enhancing Aquatic Ecosystem Research and Management

Advancement of Geospatial Capability by NRiSD and GLAHF in Enhancing Aquatic Ecosystem Research and Management Identifying, measuring, and understanding how landscape factors influence the characteristics of aquatic systems has increasingly become a central theme of research and management of rivers and lakes. Although linkages among landscapes and associated physicochemical and biological characteristics of aquatic systems have long been recognized, the development of conceptual frameworks and tools for measuring and synthesizing such linkages is relatively recent. This article summarizes the major advancements of these spatial frameworks and datasets by NRiDS and GLAHF, illustrates their uses in improving aquatic system research and management, and identifies improvements for future work.