Comparing Age and Growth of Juvenile River Herring in Freshwater and Estuarine Environments.

Burgoff, Julian*¹, Douglas Bishop¹, Allison Roy¹, Michelle Staudinger², Adrian Jordaan³,

¹U.S. Geological Survey, Massachusetts Cooperative Fish and Wildlife Research Unit, Department of Environmental Conservation,University of Massachusetts, Amherst, MA, ²U.S. Geological Survey, Northeast Climate Adaptation Center, University of Massachusetts, Amherst, MA, ³Department of Environmental Conservation, University of Massachusetts, Amherst, MA

Anadromous juvenile river herring hatched and reared in freshwater lakes during the first stage of their life emigrate into estuaries throughout the summer and fall of each year. Minimal information exists regarding the characteristics that make successful juvenile emigrants and what factors are associated with enhanced growth and survival as they transition between freshwater and estuary habitat. The objective of this research is to evaluate the age and growth of juvenile river herring in lakes and associated estuaries to better understand how egress to estuarine environments influences growth and survival. From June through October 2021 and 2022, juvenile river herring were sampled monthly using nighttime purse seines in three paired lakes and estuaries in coastal Massachusetts. In one system (Herring Run Brook, Weymouth, MA), actively emigrating juveniles were also sampled in the stream during their emigration. We analyzed daily growth increments from sagittal otoliths to compare juvenile age and growth among sites and habitat types over time. This research will contribute to a greater understanding of juvenile river herring emigration and estuary habitat use dynamics and will inform population modeling efforts by providing novel and essential biological information regarding the transition between juvenile life history stages.