Spatial distribution and environmental drivers of Northern anchovy (Engraulis mordax) from acoustic-trawl surveys along Mexico’s northwestern coast (2019–2022)

Understanding environmental selection and spatial distribution is essential for analyzing the population dynamics of small pelagic fishes. Despite their tendency to form large shoals and exhibit habitat-related spatial structure, predicting their behavior across time and space remains challenging. In the California Current System, the Northern anchovy ( Engraulis mordax ) plays a key role in energy transfer and ecosystem sustainability, supporting a transnational fishery. This study examines the spatial distribution and environmental preferences of juvenile and adult anchovies along the northwestern coast of Mexico, based on acoustic-trawl surveys conducted during summer and fall from 2019 to 2022. To characterize the physical and biogeochemical environment, in situ measurements were obtained using CTD casts at each sampling station. These profiles provided high-resolution data on temperature, salinity, dissolved oxygen, and chlorophyll fluorescence throughout the water column. Anchovies were primarily detected within the upper 180 m, with typical environmental conditions of 10.4 °C temperature, 33.9 salinity, 53.4 µmol/kg dissolved oxygen, and 0.12 relative fluorescence units. Juveniles were predominantly found offshore in deeper waters during summer, while adults were concentrated near the continental shelf north of Punta Eugenia (>27°N) during fall. Habitat suitability modeling using Random Forest algorithms revealed that coastal upwelling waters at 100 m depth were key predictors of anchovy distribution. The models highlighted dissolved oxygen, sea surface temperature, and bathymetry as the most influential variables. These findings suggest that E. mordax exhibits adaptive habitat use in response to changing oceanographic conditions. By integrating fishery-independent acoustic data with environmental modeling and in situ oceanographic observations, this study advances the understanding of anchovy habitat dynamics and supports the development of sustainable management strategies under climate variability. • According to acoustic data, the highest anchovy densities occur in upwelling areas across depths. • Coastal upwelling zones concentrate juveniles, which move offshore and deeper in summer. • Offshore and deeper movements during the 2019 El Niño suggest adaptive responses to warm events. • Offshore movement reduces exposure to warm shelf waters and to coastal fishing pressure. • Anchovies avoid southern, warm, oligotrophic waters with lower zooplankton availability.