Juvenile River Herring Habitat Use in the Connecticut River.

Roy, Allison¹, Matthew Devine², Lian Guo³, Meghna Marjadi³, Meghan-Grace Slocombe², Jacqueline Benway⁴, Justin Davis⁴, Kevin Job⁴, Adrian Jordaan⁵, Stephen McCormick⁶, Kenneth Sprankle⁷, Michelle Staudinger⁸, ¹USGS Massachusetts Cooperative Fish and Wildlife Research Unit, University of Massachusetts, Amherst, MA, ²Massachusetts Cooperative Fish and Wildlife Research Unit, Department of Environmental Conservation, University of Massachusetts, Amherst, MA, ³Organismic and Evolutionary Biology, University of Massachusetts, Amherst, ⁴Connecticut Department of Energy and Environmental Protection, Fisheries Division, Old Lyme, CT, ⁵Department of Environmental Conservation, University of Massachusetts, Amherst, ⁶USGS Eastern Ecological Science Center, S.O. Conte Anadromous Fish Research Laboratory, Turners Falls, MA, ⁷USFWS Connecticut River Fish and Wildlife Conservation Office, Sunderland, MA, ⁸USGS Department of the Interior Northeast Climate Adaptation Science Center, Amherst, MA

Decades of juvenile river herring monitoring in the mainstem of the Connecticut River and adult monitoring in tributary rivers suggest considerable interannual fluctuations in population abundance; however, little is known about juvenile river herring use of freshwater cove habitats and how this contributes to overall population viability. We aimed to characterize spatial and temporal variability in juvenile river herring densities, growth, diets, and condition among small coves along the mainstem river. Juvenile river herring were sampled using a pelagic purse seine deployed at night over four months (June, July, August, and September) in 2019. We found high variability in river herring densities among the five coves, with densities in Wethersfield Cove much higher than densities observed during sampling of coastal ponds in other studies. Sites with higher densities had lower growth rates and length at age; however, experimental studies show that food and temperature affected juvenile river herring growth. River herring consumed prey based on availability and preference for large-bodied prey items. In early summer, fish had a higher selectivity for large zooplankton (Cladocera, Copepoda) than they did for small zooplankton (Ploima); however, in late summer river herring shifted to feeding on a benthic invertebrate, Ostracoda, particularly in heavily vegetated locations. Larger juvenile river herring had higher scaled energy reserves than smaller fish, which may affect river herring survival potential. The observed spatial differences in habitat use among coves helps to understand factors limiting river herring productivity in this large river system.