Genetic connectivity of black drum ( Pogonias courbina ) stocks in the southwestern Atlantic Ocean

The delimitation of fishery stocks is an important aspect for the development and implementation of fishery stock management and sustainable use programs. Genetic analyses can provide useful information for the definition of population units, migration rates and changes in effective population sizes over long time frames. The black drum Pogonias courbina (Lacepede, 1803) is a marine fish that inhabits estuaries, bays and coastal waters of both hemispheres of the Western Atlantic, including Brazil, Uruguay and Northern Argentina. Intensely exploited at the Lagoa dos Patos Estuary in South Brazil, it is considered locally collapsed and since 2014 it is included in the National List of Endangered Fauna. Here we studied the population genetics of Pogonias courbina from South Brazil and the Argentinean and Uruguayan margins of the Río de la Plata Estuary, using the mitochondrial DNA control region. We showed that along the study area Pogonias courbina groups present high genetic diversity, no genetic structure, and are undergoing slight expansion. These characteristics favor resilience of the population, decreasing the extinction risk of local stocks. However, the slow recovery after the black drum fisheries collapse at Lagoa dos Patos indicates that the recolonization process is slow; this is corroborated by migration estimates, in which we observe a low number of migrants between Argentina/Uruguay and South Brazil. Therefore, we suggest that the South Brazil reproductive stock, impacted by regional fisheries, can be considered a unique stock in terms of management, independent of Uruguayan and Argentinean management strategies. However, an integrated management plan should ideally be considered for these groups, since impacts and conservation efforts are likely shared between areas.