The importance of environmental drivers on the narrownose smoothhound shark (Mustelus schmitti) yield in a small-scale gillnet fishery along the southern boundary of the Río de la Plata estuarine area

Abstract

Small-scale fisheries are increasingly studied around the world due to their “too big to ignore” ecological and economic impacts. Understanding their limitations and interactions with environmental dynamics is crucial for a more comprehensive management. Utilizing spring-summer gillnet fishery data from the Río de la Plata estuarine region, we addressed the influence of environmental drivers on Mustelus schmitti shark yield (individuals per 100m net and 24h soak time). In particular, we applied a two-stage boosted regression tree (Delta-BRT) approach to investigate relationships between environmental predictors and both smoothhound presence and relative yield. Results suggested that M. schmitti presence was most influenced by distance to coast, latitude and temperature, and the relative yield by distance to coast, month and wind. Fishery success was more likely to occur at long distances from the shore, southernmost locations, during early spring when temperature remains cool, and under environmental factors favouring the occurrence of the salinity front (28–30 range) over the fishing ground. Interannual differences in M. schmitti distribution were mainly explained by changes in salinity conditions driven by extreme anomalies in freshwater discharge. This study provides insight into considering environmental importance on resources availability for a more effective management of small-scale fisheries settled along environmental boundaries.