Abstract

Chilean jack mackerel (Trachurus murphyi) is a highly migratory pelagic species in the Southern Pacific Ocean, forming the most important fishery for Chile. This species undergoes extensive offshore migration toward reproductive regions beyond Chile's Exclusive Economic Zone, with the main spawning area located off central Chile. In this study, we analyze the spatial distribution of Chilean jack mackerel (CHJM) eggs using data from 14 ichthyoplankton cruises conducted between 1999 and 2018 in the spawning grounds (32-39 degrees S/74-94 degrees W), extending up to 1100 nm offshore. We also examine wind stress, Ekman transport, and sea surface temperature (SST) distribution using Empirical Orthogonal Functions (EOF). The analysis shows that CHJM spawning mainly occurs in oceanic waters between 33 degrees and 38 degrees S, extending westward from 83 degrees W to beyond 94 degrees W. Wind stress and SST climatology reveal a seasonal pattern, where the core of low wind stress coincides with 15 degrees C-17 degrees C isotherms during the spawning period (September-November). A strong spatial correlation is found between the highest CHJM egg densities and low wind stress values (< 0.02 N m(-2)) west of 85 degrees W, with an exponential decline (r(2) = 0.72) delineating the spawning area. The EOF mode 1 for environmental variables (November 1999-2018) shows low wind stress amplitudes (< 0.2 Nm(-2)) coinciding with minimal surface dynamics in the 0-25 m layer, where Ekman transport amplitudes were also low (< 0.2 m s(-1)). This stable habitat, with limited interannual variability, characterizes the CHJM spawning region and is strongly influenced by the South Pacific Anticyclone.