Hitting a moving target: Identifying critical periods for spawning and recruitment of walleye in north-temperate lakes

Fish recruitment is influenced by myriad abiotic and biotic factors that vary in space and time.  “Critical periods” may exist when the presence or absence of optimal environmental conditions determines year class strength; however, critical periods are difficult to identify quantitatively and may be altered by broad-scale stressors like climate change. We used a sliding windows analytical approach to identify potential critical temperature and precipitation windows for recruitment from a 57-year time series of walleye (Sander vitreus) spawning, adult abundance, and recruitment data. Walleye spawn timing was strongly influenced by the interaction of water temperature and photoperiod, with photoperiod cues more important when water temperatures were suboptimal for spawning. Using the full time-series, we observed no significant temperature or precipitation critical periods for walleye recruitment.  However, when dividing the data into early (1958-1984), middle (1984-2002), and recent (2003-2019) years, precipitation in the two weeks after spawning had a strong negative effect on recruitment only in recent years.  Our results suggest a growing importance of precipitation for walleye recruitment, a concern given future climate projections for a wetter Wisconsin climate.  More broadly, weak evidence for clearly defined critical periods may mean that biotic variables are more important than abiotic conditions, or that the relative importance of factors are context-dependent, complicating attempts to predict year class strength using predefined environmental variables. 

Primary Presenter: Zach Feiner, Wisconsin Department of Natural Resources (zachary.feiner@wisconsin.gov)

Authors:

Stephanie Shaw, Wisconsin Department of Natural Resources  (stephanie.shaw@wisconsin.gov)

Greg Sass, Wisconsin Department of Natural Resources  (gregory.sass@wisconsin.gov)