PROJECTS

Between 2013 and 2019 (the project is still underway), researchers encountered a total of 517 turtles, 111 of which were captured and equipped with satellite tags, including 97 green turtles and 14 hawksbill turtles. The majority of turtles spent most of their time in shallow coastal waters, with home range estimates revealing limited movements for both species. Ninety−four (89.5%) of the tracked turtles remained within a 1−3 km² area for the entire life of their tag (average tag retention time = 191 days), demonstrating limited movements and high foraging site fidelity. Notwithstanding this perspective, there were three long-distance movement patterns observed, including shifts in intra-island foraging areas (7 turtles), transitions between inter-island foraging areas (2 turtles), and a long-range migration departure out the Mariana Archipelago (1 turtle). Dive patterns suggest that both green and hawksbill turtles spend most of their time in waters shallower than 25 meters. However, it is possible that habitat partitioning may exist between the two species, with hawksbill turtles spending more time in deeper waters than green turtles, using average depths of 15.3 meters and 10.5 meters, respectively. Spatial analysis of satellite tags has demonstrated limited direct overlap of turtles with Navy detonation sites (i.e., Agat Bay Mine Neutralization Site, Piti Point Mine Neutralization Site, and Outer Apra Harbor Underwater Detonation Site). However, turtles are spending significant amounts of time in and moving through areas within 1−2 km of these sites and additional analyses are needed to better evaluate potential overlap.

The results of this work were used by the Navy to inform the analysis in the Mariana Islands Training and Testing Environmental Impact Statement proposed geographic mitigation areas and Endangered Species Act consultations.