Networks of interactions between Marine Protected Areas and their effects on the conservation of the South American sea lion and the Southern right whale in the Western South Atlantic Ocean.

Marine protected areas (MPAs) are key for biodiversity conservation and natural resource management, contributing to ecosystem services. However, fixed MPA boundaries present challenges for species with large geographic ranges, such as marine mammals. It is essential to evaluate the role of international MPA networks in protecting species like the South American sea lion (Otaria flavescens) and the Southern right whale (Eubalaena australis), whose distribution spans the southern coasts of Brazil, Uruguay, and Argentina. MPA networks can benefit from manager interactions through information exchange, knowledge sharing, and joint management strategies, addressing socio-environmental issues more effectively. In this study, we used graph theory and complex network analysis to investigate the structure of interactions among 27 MPAs based on interviews with managers across the three countries. Our findings reveal that interactions are limited to within-country networks, with no transboundary cooperation for the conservation of O. flavescens and E. australis. The networks showed low density, with geographic and hierarchical proximity influencing interaction likelihood. Management networks were generally broader than species-specific biological networks. Although our study is limited by its reliance on self-reported data and the absence of direct geospatial validation, the findings underscore critical governance gaps and emphasize the urgent need for enhanced international collaboration in the conservation of marine megafauna in the South Atlantic. Strengthening both national and transnational networks of MPAs is essential to ensure the effective protection of migratory marine species.