In 2012, Sea Sense commenced a nesting green turtle population assessment. Monitoring is intensified during the peak nesting months of April and May at Juani Island and Kigamboni District, which support Tanzania's two largest green turtle rookeries. Individual nesting females are tagged using titanium flipper tags with a TZ prefix to enable the identification of individual females. The assessment is repeated annually and is providing data on important reproductive parameters including clutch frequencies, levels of nest site fidelity and duration of inter-nesting intervals. 2021 was the ninth consecutive season of flipper tagging and the patrol teams are now encountering many turtles that have been tagged in previous nesting seasons, which is providing important insights into remigration intervals.
More than two thirds of all recorded green turtle nests in Tanzania are laid in Juani Island and Kigamboni District, so data from a continuous and focused monitoring programme can also be used to determine population sizes at other nesting sites in Tanzania where only track counts are available. Analyses of tagging data also highlight the caution needed when using track counts from daily patrols and breeding frequencies quoted in published literature (average of three clutches per season for green turtles) to estimate population sizes. Data from the population assessment have confirmed that green turtles in Tanzania frequently lay more than three clutches per season with some females laying as many as six clutches.
In 2012 Sea Sense embarked on the first ever sea turtle satellite telemetry project in Tanzania to identify migratory pathways and the location of important foraging grounds. Seven satellite tags were deployed on nesting green turtles. Three of the tags were funded by the South West Indian Ocean Fisheries Project (SWIOFP), which also funded deployment of satellite tags in Kenya, Madagascar, Mozambique, Seychelles and Mauritius. Tracking data from these countries identified Tanzania's Rufiji Delta as one of five regional 'hotspots' for green turtle foraging activity.
In light of the success of the first satellite telemetry project in 2012, Sea Sense received funding for deployment of a further four satellite tags which were deployed in Pangani, Mnemba Island (Zanzibar), Mafia and Kigamboni. Satellite tracking data are contributing to a much greater understanding of green turtle spatial dynamics both within Tanzania waters and the wider western Indian Ocean region. Tracking data demonstrates that green turtles with natal origins in Tanzania are coastal migrators, staying in inshore waters rather than crossing open seas. Two distinct post-nesting migratory strategies have been observed: northern movement along the continental shelf of east Africa to Kenya and Somalia (three turtles) and residency within Tanzania waters (five turtles). Two tags failed before post nesting migrations commenced so it was not possible to determine the migratory strategy of those two individuals.
One turtle did not fit into either strategy and instead migrated into Kenyan waters after finishing her nesting cycle but then returned to Tanzania to settle onto a foraging ground. It is unclear as to why the turtle travelled more than 1,000km before returning to a foraging ground close to her nesting beach. It is possible that she was a first time nester (neophyte) and so her navigational performance was based on limited experience.