Fish Out of Water: Predictors of Juvenile Growth, Success at Adulthood, and Year-Class Strength in Alewife (Alosa pseudoharengus).

Colby, Rebecca S.¹, Eric Schultz², ¹MassWildlife Central District, West Boylston, MA, ²University of Connecticut, Storrs, CT

The increasing frequency and severity of drought in coastal U.S. regions threatens and degrades connections between freshwater and seawater habitats. If droughts occur during diadromous fish migrations, lost or compromised habitat connectivity could obstruct passage between natal and adult growth grounds. This could have great impact on juveniles attempting their very first migration and salinity transition, especially when considering underlying physiological states. Some Alewife (Alosa pseudoharengus) populations in particular rely on smaller streams for migratory passage, exacerbating their vulnerability to the impacts of low water availability. We leveraged historical information on the Alewife run at Bride Lake (East Lyme, CT, USA) to investigate water availability in the natal habitat as a predictor of juvenile growth and success at adulthood, and adult condition as a predictor of overall year-class strength. Our findings suggest that low water availability at the juvenile stage, especially driven by mid- to late-May regional drought, is a predictor of reduced juvenile growth and iteroparity. Additionally, age at first spawn and iteroparity are predictors of year-class strength. The predictors identified in this study could serve as low-effort monitoring targets for Alewife populations (if validated at other sites), especially if a risk assessment of Alewife runs were performed to identify those most vulnerable to impacts from drought. Increasing our understanding of how juveniles interact with their environment during migration is crucial for current-day management practices for diadromous species, as well as for demystifying the shaping forces of lifestyles involving salinity transitions.