Population structure of the Chub mackerel Scomber japonicus, in waters of the northwest of Mexico

Abstract

Understanding the population structure of commercially harvested species is essential for the effective management of fisheries. The Chub mackerel (Scomber japonicus) is a significant fishery resource in the Mexican Pacific. It exhibits two distinct population units delineated by temporal variations in gonadal maturity stages and spawning seasons, and other features as age and size composition. However, the species' highly migratory behavior may contribute to genetic homogeneity, similar to what has been observed in other small pelagic species. This study aimed to test whether the Chub mackerel presents a discrete population by integrating body morphological (geometric morphometric) and genomic (SNP´s) variability analyses. Fish analyzed were collected in Ensenada, Bahía Magdalena, Mazatlán, and the Gulf of California center from autumn 2020 to spring 2021 (N = 291). The body morphological variability (geometric morphometrics) allowed us to differentiate between two morphotypes: one with an elongated and hydrodynamic shape related to the areas with higher current intensity, followed by weaker covariation with increasing temperature; and the second, with a shorter head associated with less dynamic waters and sea surface height increased. However, the population genomic analysis with 4877 neutral SNPs showed a single population in the Mexican Pacific. These results indicate that the Chub mackerel presents a single population with two morphotypes linked to the variability of ocean dynamics.