Overwinter Survival of Age‐0 Gizzard Shad in Missouri Reservoirs Spanning a Productivity Gradient: Roles of Body Size and Winter Severity

Abstract

AbstractSurvival through the first winter of life can be an important bottleneck in the recruitment of fishes and is commonly size dependent, with larger fish exhibiting higher survival than smaller fish. Body size and density of age‐0 gizzard shad Dorosoma cepedianum, an ecologically important prey species, are reportedly influenced by reservoir productivity. These differences in age‐0 demographics across a productivity gradient may influence overwinter survival and subsequent year‐class strength of adults. I examined fall age‐0 demographics (fall mean total length, mean density, and energy density), overwinter changes in these demographics, and factors that influenced overwinter survival among five age‐0 cohorts in five Missouri reservoirs spanning a productivity gradient. I specifically wanted to determine whether (1) fall age‐0 demographics varied along a reservoir productivity gradient, (2) fall age‐0 demographics and winter severity were related to overwinter survival, and (3) variation in the abundance of overwinter survivors among years decreased with increasing reservoir productivity. Fall demographics did not consistently vary along a productivity gradient. Fall total length was typically larger in more productive reservoirs and was the most variable in the least productive reservoir, with large fish being present during 1 year. Likewise, fall density did not vary with reservoir productivity; the highest overall density occurred in one slightly eutrophic reservoir and one highly eutrophic reservoir, and fall density was lowest and most variable in the least productive reservoir. However, energy density was higher in the more productive reservoirs than in the less productive ones. Overwinter survival ranged from 0% to 100% and increased with increasing fall total length and winter temperatures among all cohorts and reservoirs. Variation in overwinter survivor abundance did not consistently decrease along a reservoir productivity gradient. Unique characteristics of individual reservoirs and changing climatic conditions apparently obscured overall patterns in age‐0 demographics and overwinter survival across reservoir productivity.