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AUTHORS: Brett T. Miller, Brian C. Peterson - Department of Biology, University of Nebraska at Kearney; Casey W. Schoenebeck, Department of Biology, University of Nebraska at Kearney and Minnesota Department of Natural Resources, Glenwood Area Fisheries Office; Keith D. Koupal, Nebraska Game and Parks Commission, Fisheries Division
ABSTRACT: Gizzard shad (Dorosoma cepedianum) are an influential forage fish in many reservoirs across their native range. The importance in understanding what biotic and abiotic factors influence larval gizzard shad abundance can link timing of peak densities to sportfish management. The goal of this study was to investigate what biotic and abiotic factors influence larval gizzard shad abundance. We used combinations of 6 variables (total zooplankton, adult gizzard shad CPUE from the fall prior, temperature, turbidity, chlorophyll a, and reservoir elevation) from a long-term (2003-2014) monitoring database to create 26 a priori candidate models to assess the relative support of explanatory variables using Akaike’s information criterion (AIC). During the course of our study, larval gizzard shad densities ranged from 0.6±0.2 to 5.6±1.4/m3 SE which is similar to reported regional densities. The best supported model included turbidity and total zooplankton. Turbidity has been shown to reduce visual effectiveness of predators and allow larval gizzard shad to congregate closer to the surface where zooplankton are more abundant. Increase in total zooplankton provides greater food availability which has been shown to increase larval gizzard shad growth, thus improving the escape ability from predators, but also grow past the gape restriction of potential predators. Results suggest that a combination of factors drive larval gizzard shad abundance, understanding and being able to predict what conditions may produce a large year class can be utilized by fisheries managers to better understand competition with sportfish as well as stocking strategies.
