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.