Mentor: Karly Geller, Ph.D.

Shifts in environmental conditions can impact fish distributions, phenology, community composition, and population abundance. Here, we use 18 years of larval fish data to investigate bluegill (Lepomis macrochirus) hatch seasonality, abundance, and survival rate in a hypereutrophic reservoir. Along with gizzard shad (Dorosoma cepedianum), bluegill is one of the most abundant and ecologically important fish species in midwestern reservoirs. Larval bluegill were collected weekly via tows at two offshore sites in Acton Lake (USA) (April - August, 2007 - 2024) to quantify larval abundance and size. For determining the age of collected fish, estimated bluegill growth rates were used, allowing us to predict hatch dates and assess long-term trends. We found that larval bluegill density in the reservoir is increasing over time (18 years), and a preliminary analysis on a subset of years suggests that both the yearly date of peak abundance and peak hatch may be occurring earlier in the summer compared to the beginning of our study. We also observed that the density of bluegill at hatch decreases over the course of a summer, and hatch dynamics vary substantially year-to-year (i.e., one major hatch vs up to 8 hatch cycles per year). Additionally, our study shows that several abiotic and biotic drivers mediate long-term larval bluegill trends and seasonal hatch dynamics. Our results demonstrate that while larval bluegill hatch dynamics are highly variable, we can improve our understanding by incorporating key physical and biological conditions of the lake.

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