Influence of Sea Surface Temperature and Chlorophyll-a on Biomass Availability and Body Size of the Black Skipjack (Euthynnus lineatus) in the Mexican South Pacific

Abstract This study investigates the relationship between oceanographic variability, specifically sea surface temperature ( SST ) and chlorophyll- a (Chl- a ) concentration, and the abundance and size structure of Euthynnus lineatus (black skipjack) along the southern Pacific coast of Mexico from October 2022 to October 2024. The region experiences two distinct seasons: a dry season with strong “Tehuano” winds causing upwelling, and a rainy season influenced by the Costa Rica Coastal Current. High-resolution satellite data were integrated with biometric and catch data from local artisanal fisheries. Seasonal catch patterns peaked between April and July, following increased productivity and rising SST. The highest catches coincided with SST around 31.0°C, suggesting a thermal preference that enhances aggregation and catchability. Significant interannual variability was observed; 2023 catches were more than double those of 2024, likely associated with the presence of a warm pool in 2023 and varying environmental conditions. Morphometric analysis indicated larger individuals during cooler, productive months (October–March) and smaller fish during warmer periods, possibly due to temperature-driven metabolic responses. Principal component analysis (PC1: 38.4%; PC2: 27.7%) confirmed a strong seasonal modulation of environmental and biological variables. These findings suggest that monthly SST and Chl- a variability are primary drivers of E. lineatus dynamics in Oaxaca, providing essential data for sustainable fisheries management and assessing the impacts of climate change and extreme events on artisanal fisheries.