Biological indicators of climate change: trends in fish communities and the timing of walleye spawning runs in Minnesota.

Abstract

I conducted research on two projects to examine effects of climate change on Minnesota’s aquatic communities. I used walleye egg-take records from the Minnesota Department of Natural Resources for 12 spawning locations and historical ice-out data to determine if the timing of these events is changing. I used ice-out data instead of temperature for our analyses because historical temperature data is not available and ice-out has been previously related to climate change. Because ice-out has been previously related to climate change, I regressed the dates of first egg-take against ice-out dates to determine if the timing of walleye spawning runs could be a useful biological indicator of climate change. For the second project to determine if fish species abundances are changing in response to climate change, I used historical lake survey records for 34 lakes, each with 15 to 43 years of data, and regressed catch-per-unit-effort (CPUE) against year. I examined species distributions by regressing mean latitude against year. I regressed slopes of CPUE over time against 5 local air temperature variables to determine if changes in abundance were associated with air temperature. I also used stepwise regressions (forward and backward selection) and one-way analysis of variance (ANOVA) to determine if variability in trends could be explained by lake physical and chemical characteristics. Results were reported for 7 species with the strongest trends: Centrarchids (Micropterus salmoides, Micropterus dolomieu, and Lepomis macrochirus); Ictalurids (Ameiurus melas and Ameiurus natalis); Whitefish (Coregonus artedi and Coregonus clupaeformis).For the walleye spawning analyses I found that spawning runs and ice-out are occurring earlier in some lakes but not all. However, there was a strong relationship between first eggtake and ice-out dates, and walleye egg-take appears to provide a good biological indicator of climate change. For the lake survey analysis, centrarchid abundance in lakes was increasing over time, black bullhead abundance was decreasing, and other species were increasing in some lakes and decreasing in others. Slopes of CPUE versus year increased more quickly over time in smaller lakes and more quickly moving east across the state than in larger lakes toward the west. All species’ ranges were significantly advancing northward except smallmouth bass and whitefish. Regressions of CPUE versus air temperature showed that centrarchids are increasing in lakes as summer air temperatures increase, and whitefish are decreasing in lakes as air temperatures increase. In summary, the abundances and distributions of these 7 species over time may be responsive to climate change, and trends for species abundances may be influenced by lake characteristics. Centrarchids and bullhead may be good indicators, and thus, further research is warranted. Also, because there is a strong relationship between dates of first egg-take and ice-out, and because ice-out has previously been related to climate change, the timing of walleye spawning runs may be a useful biological indicator of climate change.