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

ABSTRACT 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.