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Multiple threats analysis for loggerhead sea turtles in the Southwest Atlantic Ocean

Milagros López-Mendilaharsu*, Bruno Giffoni, Danielle Monteiro, Laura Prosdocimi, Gabriela M. Vélez-Rubio, Alejandro Fallabrino, Andrés Estrades, Alexsandro Santana dos Santos, Paulo H. Lara, Thais Pires, Manjula Tiwari, Alan B. Bolten, Maria Ângela Marcovaldi

*Corresponding author:

ABSTRACT: Priority setting approaches for widely distributed and long-lived species can be challenging. This is especially true for sea turtles, which are species of conservation concern. The aim of this study was to conduct a detailed analysis of threats to identify, quantify and prioritize the main impacts to the loggerhead (Caretta caretta) population in the South West Atlantic (SWA) region. A matrix of relative threats was constructed. Threats were identified and classified for 8 different life stages (nesting females, eggs, hatchlings, swim-frenzy transitional stage, juveniles neritic, juvenile oceanic, adult neritic, adult oceanic) and ecosystems inhabited by sea turtles (terrestrial, neritic and oceanic). Results indicated that fisheries bycatch represents a major threat for loggerheads in the SWA. The trawl fishery was identified as the main source of mortality for neritic juvenile and adult turtles, whereas juveniles in oceanic areas were mostly impacted by the surface longlines. In terrestrial environments, eggs and hatchlings are mainly affected by habitat alteration, and by native and exotic predators. Loggerheads have shown a positive nesting trend at their main nesting beaches in the SWA, probably due to long-term conservation efforts to reduce the mortality of the different life-stages within the terrestrial zone. However, the high mortality rates of juveniles and sub-adults documented at some known foraging grounds represent a reason for concern as this may affect the overall population trend in the future. In conclusion, this threat analysis provides a tool to review the goals of national action plans, prioritize actions, and optimize the allocation of management resources.