Trends in pinniped interactions with commercial passenger fisheries vessels in California

Abstract

The resurgence of pinniped populations along the West Coast of the United States, a consequence of the Marine Mammal Protection Act, has resulted in unintended ecological and socio-economic repercussions. The conflict between pinniped and fisheries in California, a persistent management challenge for decades, primarily manifests as depredation (the removal or damage of hooked fish) from Commercial Passenger Fishing Vessels (CPFVs). Depredation not only results in stolen fish but also in lost fishing opportunities due to the presence of pinnipeds deterring target fish species or necessitating vessel relocation. Using logbook data from 1994 to 2021, we explored spatiotemporal trends in pinniped depredation of CPFVs in California. Our model, which evaluates the factors predicting the number of fish depredated, revealed a distinct concentration of pinniped depredation in Southern California, with increasing rates of depredation during summer and spring. Over our time series, depredation is decreasing, as our model found a seven percent decrease in the number of fish depredated each calendar year. Correspondingly, changepoint and trend analysis revealed two key trend reversals in 1999 and 2014, exemplified by a rapid peak and ensuing drop in overall depredation. Overall, our study suggests that depredation is shaped by an interplay of environmental factors, the population dynamics of pinnipeds, and the patterns of fishing activities within the California current ecosystem.