Resilience despite overfishing? Microsatellites reveal high genetic diversity and connectivity for Umbrina canosai (Acanthuriformes: Sciaenidae) in the Southwestern Atlantic

Abstract

Abstract Marine connectivity and demographic changes are important factors in the conservation and management of commercially exploited marine fishes. This study used seven microsatellite markers to evaluate the connectivity and potential loss of genetic diversity for the Argentine croaker (Umbrina canosai), a coastal sciaenid fish endemic to the Warm Temperate Southwestern Atlantic Province. Sampling was conducted across almost the entire species distribution: Southeastern Brazil, Southern Brazil, and Argentine-Uruguayan Common Fishing Zone. Despite historical overfishing, the analyses revealed high genetic diversity and connectivity, with no evidence of a genetic bottleneck. Previous studies based on phenotypical and ecological markers have proposed two distinct stocks for U. canosai. We hypothesized that a bidirectional gene flow between these stocks is promoted by the dispersal of planktonic eggs and larvae via marine currents in the Southwestern Atlantic, as well as by adult migrants. These conclusions support the species resilience and its IUCN classification as “Least Concern”. Nevertheless, transboundary management measures by Brazil, Uruguay, and Argentina are necessary to prevent the economic collapse of U. canosai stocks.