Post-nesting migrations of green turtles from Aldabra Atoll, Seychelles: satellite tracking, flipper tag returns and marine protected areas

Abstract

To effectively implement protective measures for migratory species such as marine turtles, knowledge of their breeding grounds, foraging areas, migratory pathways and possible threats encountered is required. Aldabra Atoll, a UNESCO World Heritage site in Seychelles, hosts and protects one of the largest nesting populations of green turtles Chelonia mydas in the Western Indian Ocean. We satellite tracked 21 post-nesting green turtles during 2011-2014 (n = 8) and in 2022 (n = 13). Nineteen turtles were tracked beyond Aldabra and took 8-49 d to reach their final recorded locations, travelling 743-2552 km along distinct routes, each taking a unique path to widely dispersed coastal sites in Tanzania, Madagascar, Somalia, Kenya, Mozambique and Seychelles, highlighting the connectivity of the region through one large rookery. When compared to the locations of 54 international flipper tag returns from Aldabra females recorded since the 1980s, there was consistency in the use of Tanzania, Kenya, Mozambique, Somalia and Madagascar as foraging destination countries for Aldabra turtles. However, satellite tracking expanded the countries used as foraging sites to include Seychelles and elevated the relative importance of remote sites for which fishermen were unlikely to report intercepted flipper tags—especially Somalia, northern Madagascar and distant offshore foraging habitat within Seychelles. The end points for >40% of the turtles were within or nearby marine protected areas (MPAs) in Madagascar, Mozambique, Tanzania and Seychelles, 5 (26.3%) within MPAs and 3 (15.8%) <25 km away from MPAs. Eleven (57.9%) turtles travelled through MPAs after leaving the Aldabra protected zone. There is further opportunity to increase the protection and connectivity of foraging areas by expanding existing MPAs. Identifying foraging hot spots within the region by pooling data from other important breeding grounds should be a priority to focus conservation efforts on migratory corridors and the status and state of those foraging areas.