Changes in the Spawning Phenology of the Anchoveta Engraulis ringens Over Two Decades as Related to Environmental Drivers in the Humboldt Upwelling System

Resumen: In recent decades, changes in the reproductive phenology of marine fishes in response to climate variability have become a concern for fisheries scientists. This study investigates long-term shifts in the spawning phenology of anchoveta (Engraulis ringens) using a 22-year dataset and a generalized additive model (GAM), relating spawning index with key environmental drivers of coastal upwelling (standardized upwelling index, Ekman transport and pumping, sea surface temperature (SST), and chlorophyll-a concentration) as well as biological traits such as female body condition (Kn), weight, and mean fish length. Four major findings emerged: (i) interannual and seasonal changes in fertilization levels; (ii) a transition from a single winter–spring spawning peak before 2015 to a bimodal pattern after 2015, with the appearance of a secondary summer peak; (ii) a weakening of the main winter–spring upwelling signal over time, accompanied by warmer SST and lower chlorophyll-a, whereas the summer peak coincided with stronger upwelling and cooler SST; (iii) a general decline in overall reproductive intensity despite the rise of summer spawning activity; and (iv) evidence that both spawning periods occur independently of female size, with individuals larger than 13 cm participating in both events. The GAM model explained 52% of total variability in the spawning index, with season (50%), period (before vs. after 2014) (18%), SST (28%), and the standardized Ekman Index (6%) as the most influential predictors. Overall, our results demonstrate a shift in anchovy reproductive strategies, likely driven by changes in upwelling dynamics, with potential implications for ecosystem functioning and fisheries management in the Humboldt Current system.