Black Crappie Influences on Walleye Natural Recruitment in Northern Wisconsin Lakes

Walleye Sander vitreus natural recruitment has declined in northern Wisconsin lakes over time. Several factors have been implicated to explain Walleye natural recruitment declines in Wisconsin, including climate change, Largemouth Bass Micropterus salmoides interactions, less desirable fish communities, production overharvest, and depensatory effects on recruit survival. Previous research in other systems has suggested that White Crappie Pomoxis annularis negatively influence Walleye recruitment, but interactions between Walleye recruitment and Black Crappie Pomoxis nigromaculatus have not been examined. We evaluated trends between Black Crappie and age-0 Walleye relative abundance (catch per effort [CPE]) collected in northern Wisconsin during 1991-2017. Specifically, we tested for (1) trends in age-0 Walleye and Black Crappie CPE over time, (2) a relationship between age-0 Walleye and Black Crappie CPE, and (3) the influence of several abiotic and biotic covariates (including Black Crappie CPE) on age-0 Walleye recruitment. Age-0 Walleye CPE declined and Black Crappie CPE increased significantly during 1991-2017. Within lakes, the relationship between age-0 Walleye and Black Crappie CPE showed a threshold effect such that age-0 Walleye CPE was always low when Black Crappie CPE was high. Of the abiotic and biotic covariates tested to explain variability in the age-0 Walleye and Black Crappie CPE relationship, only Black Crappie CPE was significant. Our results suggest that Black Crappie may negatively influence Walleye natural recruitment; however, we caution that our findings only reveal a pattern and not a mechanistic explanation for negative interactions between the species. Additional research is needed to test for mechanistic interactions between Walleye and Black Crappie and to inform comanagement of these species.