Long-term spatial and temporal patterns of sea turtle strandings in southern Brazil

Abstract

Strandings of marine vertebrates along beaches have been widely used to infer threats and causes of mortality in adjacent waters. Understanding the influence of anthropogenic impacts on sea turtle survival is essential for effective conservation, yet limited data are available on the magnitude and patterns of sea turtle mortalities in southern Brazil. Our study reports sea turtle stranding data obtained from monthly beach surveys undertaken from 1995 to 2014 in the state of Rio Grande do Sul, Brazil, and when possible, we identify causes of mortality associated with different fisheries. A total of 6285 turtles of five species were encountered, with the three most common species being loggerhead (Caretta caretta; n = 3192), green (Chelonia mydas; n = 2572), and leatherback turtles (Dermochelys coriacea; n = 376). Generalized linear models demonstrated that loggerhead and green turtle strandings have increased over the last 10 years. Strandings were highest from October to March, which coincides with the greatest bottom pair trawl, gill net, and possibly double-rig trawl fishing effort near the coast. Our results provide a baseline to compare future sea turtle stranding patterns. For reducing sea turtle mortalities, we suggest that time/area closures and/or reduction in gill net, pair trawl, and possibly double-rig trawl fishing effort in coastal waters of southern Brazil during austral spring and summer be considered for future fisheries management plans.