Long-term changes in biotic and abiotic factors influence larval gizzard shad (Dorosoma cepedianum) annual peak density

Abstract

ABSTRACTGizzard shad (Dorosoma cepedianum) are an influential forage fish and driver of zooplankton resources in many reservoirs. The ability to identify the biotic and abiotic factors that influence the timing of elevated gizzard shad densities can be important to better utilize this forage fish and manage sport fish. The objective of this study was to investigate which biotic and abiotic factors influence larval gizzard shad annual peak density. We used combinations of six variables (CPUE of adult gizzard shad from the prior fall, mean zooplankton density, turbidity, chlorophyll a, relative reservoir elevation, and water temperature) from a long-term (2003–2014) monitoring program to create 28 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 annual peak densities were best explained by zooplankton density and relative reservoir elevation. Zooplankton density provides greater food availability which has been shown to increase larval gizzard shad growth. Relative reservoir elevation was negatively associated with higher densities of larval gizzard shad. This study describes two important factors that may result in greater larval gizzard shad densities, which can assist managers in anticipating available forage for sport fish and identify strategies to improve system management.