Seasonal variation and response of surf zone fish assemblages to environmental variables in the Northeast Pacific

Located at the land-sea interface, the highly dynamic sandy beach and surf zone ecosystem is one of the coastal zones used most intensely by humans (e.g., recreation, fishing, tourism). Surf zones are also important as fish habitat; however, the factors structuring fish assemblages in the surf zone are relatively understudied due to challenges associated with sampling this dynamic environment. To investigate temporal influences on surf zone fish communities, we evaluated seasonal trends in the fish assemblage and associations with environmental conditions using baited remote underwater video stations (BRUVS) at four beaches on the Northeast Pacific coast (California, USA) from July 2020 to June 2021. Our study region is characterized by strong seasonality in productivity (due to spring upwelling) and the wave climate (in response to winter storms), making it an ideal location for evaluating seasonal change in surf zone fish. We found that surf zone fish assemblages exhibited marked seasonality and site-to-site variability. Two species of surfperch (Amphistichus argenteus and A. koelzi) and leopard sharks (Triakis semifasciata) were more common in the winter and spring, corresponding with surfperch spawning, while flatfishes were more abundant in the summer. Fish species composition was most affected by distance from shore (as a proxy for surf zone width), visibility, water temperature, percent cover of combined macroalgae and surfgrass, and breaker wave height, with significant effects detected for distance from shore and breaker height. Fish species that exhibited higher abundance in the winter, including A. argenteus, A. koelzi, and T. semifasciata, were associated with larger waves and wider surf zones. Our results highlight the influence of seasonal variation in environmental conditions on fish communities in the dynamic, coastal surf zone ecosystem, with potential management implications for several highly abundant species targeted by recreational fisheries.