Tipping the Scales: Comparing Abundance, Biomass and Length of Banded Killifish (Fundulus diaphanus) and Redbreast Sunfish (Lepomis auritus) across multiple tributaries of the Delaware River Estuary, USA

• Eli Swope, Marine Science, University of Delaware

• Edward Hale, Marine Science, University of Delaware

Biomass of fishes is used in the global management of recreational and commercial fisheries, as well as in estimating habitat production. Habitats with higher fish biomass generally enhance biodiversity. However dams that impede fish passage can create habitat fragmentation, as well as reduce fish production and biodiversity. We measured fish biomass across three tributaries of the Delaware River- Brandywine River (BR), White Clay Creek (WCC), and Red Clay Creek (RCC) for two resident fish species, Banded Killifish Fundulus diaphanus and Redbreast Sunfish Lepomis auritus above and below dams at each location. We compared fish biomass in these waterways to provide a broader understanding of the impact of impediments to fish passage. We used two replicate haul seines to collect samples from 8 locations weekly from July 2, 2024 to July 29, 2024. We found no statistically significant difference in biomass of Banded Killifish (p-value = 0.231) or Redbreast Sunfish (p-value = 0.134) between the three tributaries when sites were aggregated. However, the biomass of Banded Killifish was significantly higher at sites below dams (p-value = .0109) compared to sites above dams, while Redbreast Sunfish biomass did not significantly differ at sites above vs. below dams (p-value = 0.177). Our results demonstrate that biomass across tributaries when locations are pooled together is similar in tributaries of the Delaware River, but that dams negatively affect the biomass and production of forage fish, specifically Banded Killifish within a given tributary. Our findings suggest that impediments to fish passage interrupt the transfer of biomass and energy of a key forage species at sub-tributary level spatial scales.