Timing of Walleye Spawning as an Indicator of Climate Change

We obtained Minnesota Department of Natural Resources historical records describing the egg-take from walleyes Sander vitreus at 12 spawning locations to determine whether the timing of walleye spawning runs could be used as an indicator of climate change. We used ice-out data instead of temperature for our analyses because walleyes often spawn soon after ice-out, and ice-out has been previously related to climate change. We used linear regressions to determine (1) the relationship between the start of spawning (based on first egg-take) or peak of the spawning run (greatest egg-take) and ice-out date and (2) whether long-term trends existed in ice-out and date of spawning over time. Linear regressions of the date of first walleye egg-take versus ice-out date showed that walleye spawning begins 0.5-1.0 d earlier for each 1.0-d decrease in ice-out date. All but two regressions had slopes less than 1.0. Similar results were found for peak of spawning runs. Regressions of egg-take and ice-out date versus year showed trends toward both earlier spawning and earlier ice-out. For regressions of first egg-take versus year (16 total with restricted data sets), significant negative slopes (P < 0.10) were observed in 5 of 16 regressions; for peak egg-take, six regressions had significant negative slopes. For regressions of ice-out date versus year, 25 of 26 regressions were negative; there were nine significant negative slopes (P < 0.10). Overall, ice-out and walleye spawning are occurring earlier in Minnesota, and the timing of walleye spawning may be a good biological indicator of climate change.