Changes in Relative Abundance of Several Minnesota Fishes from 1970 to 2013

Abstract

Large‐scale ecological stressors such as climate change, habitat degradation, and invasive species increasingly affect fisheries across watershed or political boundaries within which they are typically managed. Though broad‐scale analyses of trends in fish populations and changes in aquatic communities can be useful for detecting the effects of these stressors, they are rarely possible due to a lack of long‐term data sets. The Minnesota Department of Natural Resources has used gill nets and trap nets to monitor fish communities in lakes since 1940, and the techniques have been standardized since 1970. We applied a random‐coefficient mixed‐effects model to mean CPUE data to describe statewide and local population trends of eight key fish species (Black Crappie Pomoxis nigromaculatus, Bluegill Lepomis macrochirus, Largemouth Bass Micropterus salmoides, Northern Pike Esox lucius, Smallmouth Bass M. dolomieu, Walleye Sander vitreus, White Sucker Catostomus commersonii, and Yellow Perch Perca flavescens) sampled from 1970 to 2013 in 119–1,499 lakes. We found increasing statewide trends in gill‐net CPUE of Black Crappie, Bluegill, Largemouth Bass, Smallmouth Bass, Northern Pike, and Walleye and decreasing trends for Yellow Perch and White Sucker. Statewide trends in average trap‐net CPUE were positive for Bluegill, negative for Black Crappie, Walleye, White Sucker, and Yellow Perch, and stable for Largemouth Bass, Northern Pike, and Smallmouth Bass. We compared the CPUE trends across lake types developed for Minnesota lakes and found some differences, especially in medium and large mesotrophic lakes, suggesting that some species display changes in abundance more in those lakes types than in others. This study quantifies temporal changes in Minnesota's fish community structure and can help managers focus future research and management activities in the state and in similar waters across central North America. Received May 14, 2014; accepted September 9, 2014

An Assessment Model for a Standard Gill Net Incorporating Direct and Indirect Selectivity Applied to Walleye

“…Because our model is based on statewide data, it is likely to have some generality but the scatter of points in Figure about the line of direct proportionality and the random lake effects in the models for statewide trends (Grant et al. 2004b; Bethke and Staples ) suggest that average catchability likely varies among lakes. The use of fixed net sites rather than randomized locations in Minnesota's standard surveys also contributes to such variation.…”

“…As shown with the Mille Lacs and Upper Red Lake examples, the 80% probability distribution of the predicted Walleye density by length-bins for fish measuring between 356 and 510 mm could be plus or minus 20% to 30%. Because our model is based on statewide data, it is likely to have some generality but the scatter of points in Figure 1 about the line of direct proportionality and the random lake effects in the models for statewide trends (Grant et al 2004b;Bethke and Staples 2015) suggest that average catchability likely varies among lakes. The use of fixed net sites rather than randomized locations in Minnesota's standard surveys also contributes to such variation.…”

“…Second, we suggest that researchers develop methods to directly estimate capture probability by size and test the assumptions of indirect selectivity models. Lastly, some management questions about trends and changes in stock status may be addressed by analyses of raw gill-net catch rates and size distributions (Grant et al 2004b;Bethke and Staples 2015); however, questions about the abundance and size distribution of the populations require considering size selectivity and capture probability. Not addressing selectivity biases the estimates of vital statistics, and adjusting gill-net catch data with indirect selectivity models that assume equal contact probabilities for each mesh may introduce considerable bias to estimates of population abundance and length distributions.…”

Life history constraints explain negative relationship between fish productivity and dissolved organic carbon in lakes

“…As bluegill are primarily a littoral species, particularly in spring and early summer (Becker, 1983), fish were collected using littoral fyke nets set overnight (2-10 net nights per lake per year), with the exception of McCullough where we were restricted to angling. Fyke nets have shown to be a reliable method to sample bluegill populations, yielding similar results to various other gears (Bethke & Staples, 2015;Fischer & Quist, 2014). For each sampling occasion, one 1-m² square net (12-m leader, no wings, 3-m-long car with 5 sections), and one 1-m-diameter round net (12-m leader, two wings of 6 m, 2.5-m-long car with 4 sections) were set (both with a stretched mesh size of 1 inch, and 1-m-high leaders).…”

Quantifying Temporal Trends in Fisheries Abundance Using Bayesian Dynamic Linear Models: A Case Study of Riverine Smallmouth Bass Populations

“…In addition, there is an increasing emphasis on understanding and managing aquatic systems across large spatial extents as opposed to single-lake or single-watershed management (Midway et al 2016). For example, Bethke and Staples (2015) performed a broad-scale analysis of fish population trends in Minnesota lakes in an effort to place locally observed changes into a larger context and to assist managers in preparing for future large-scale management of important fishery resources. Similar regional analyses have been completed in Wisconsin lakes for both Walleyes Sander vitreus and Largemouth Bass Micropterus salmoides in an effort to understand temporal changes in fish populations relative to interspecific and intraspecific competition and in the context of management regulations (Hansen et al 2015b;Pederson et al, in press).…”