Zebro, L.R., J.T. Mrnak, S.L. Shaw, S.R. Chipps, and G.G. Sass. 2022. Density-Dependent, Cannibalism, and Environmental Influences on Juvenile Walleye Survivorship in Northern Wisconsin Lakes. Fisheries Management and Ecology 29:897-910.
Abstract
Walleye (Sander vitreus) natural recruitment has declined in many populations within the Ceded Territory of Wisconsin (CTWI) over the past twenty years. Using CTWI age-0 and age-1 walleye relative abundance (CPE) data during 1990-2019, we tested for abiotic and biotic (density dependence, cannibalism) factors influencing age-0 to age-1 walleye mortality. Age-0 to age-1 walleye mortality was strongly density-dependent. Juvenile walleye mortality was always elevated at high age-0 CPE and highly variable at low age-0 CPE. Cannibalism effects did not influence age-0 to age-1 walleye mortality. Mixed effects modeling results suggested that age-0 CPE (positive), May surface water temperature (positive), and peak surface water temperature (negative) were the strongest predictors of age-0 to age-1 walleye mortality. Our results suggest that density-dependence and environmental factors influencing spawning and ontogenetic phenology (climate change, variable ice-off dates), trophic mismatches, and metabolic and consumptive demand may dictate age-0 to age-1 walleye mortality. Our results also showed elevated age-0 to age-1 walleye mortality at low age-0 CPE, which supports previous findings of depensatory recruitment dynamics in CTWI walleye populations. Given observed natural recruitment declines observed in CTWI walleye populations over time, stocking has been primarily used to rehabilitate stocks. Our findings suggest that stocking on top of natural recruitment would further increase density-dependent juvenile walleye mortality rates. Additional research is needed to specifically address elevated juvenile walleye mortality at low adult stock sizes and/or with declining natural recruitment to inform conservation management decisions.