Larval fish population dynamics are influenced by biotic and abiotic factors. Larval stages of planktivorous fish temporally overlap in aquatic systems. In midwestern reservoirs in the USA, larval stages of gizzard shad (Dorosoma cepedianum) and bluegill (Lepomis macrochirus) temporally overlap in early-mid summer. Larval gizzard shad hatch earlier (early May) than bluegill (June) and can cause short-term decreases in zooplankton density, therefore altering food resources for larval bluegill. Turbidity can decrease larval predation risk as well as alter larval fish-prey interactions by affecting prey contrast, while temperature affects larval fish growth rates. In order to determine biotic and abiotic drivers of larval bluegill density we analyzed an 11-year data set (2006-2017) in a eutrophic reservoir of weekly measurements of larval fish and zooplankton density, temperature and inorganic turbidity (Non-volatile suspended solids, NVSS) from May to August. Preliminary analysis showed an increase in mean density of bluegill and gizzard shad larvae with time. However, gizzard shad larvae density was consistently higher than bluegill larvae density. Temperature and NVSS also increased with time, while total zooplankton density showed no major trend with time. Larval bluegill density only showed strong positive correlations with temperature and NVSS. Larval bluegill density showed no correlations with biotic factors, larval gizzard shad and zooplankton density. Our results suggest that the negative effects of the temporal overlap between bluegill and gizzard shad larvae may be alleviated in high turbidity habitats. High turbidity may decrease bluegill larvae predation risk and/or an increase zooplankton availability via changes in prey contrast.
Author(s): Jonathan Hauman, Biology and Environmental Science Major
Advisor(s): Maria Gonzalez, Department of Biology
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