Incorporating key environmental drivers in European anchovy (Engraulis encrasicolus) stock assessment model in the Adriatic Sea

Recent advancements in integrated single-species models allow for the inclusion of environmental drivers in stock assessment models, improving stock evaluation and better explaining fish population dynamics. This study applies Stock Synthesis (SS) to assess the European anchovy (Engraulis encrasicolus) stock in the Adriatic Sea, allowing for time-varying growth, recruitment, mortality, and survey catchability. These processes were linked to sea surface temperature (SST), river runoff, chlorophyll-a concentration, and salinity. Model selection, based on AIC and parameter significance, revealed that higher SST is significantly associated with reduced mean length-at-age. Two-variable models further revealed that SST strongly influences growth, while freshwater input modulates mortality at age one and survey catchability. Integrating these environmental factors reduced unexplained recruitment variability and improved model fit to length- and age-composition data, enhancing stock status estimates such as spawning biomass and fishing mortality. Diagnostic evaluations indicate that the integration of environmental covariates, despite inherent challenges associated with data quality, offers valuable insights into the observed declines in anchovy size and recruitment. The findings emphasize the importance of environmental conditions—particularly temperature and freshwater discharge—in driving life-history traits and population dynamics.