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Sea turtle tagging in the Mariana Islands Training and Testing (MITT) study area
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Sea turtle tagging in the Mariana Islands Training and Testing (MITT) study area
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  • Alternative Title:
    Sea turtle tagging in the Mariana Islands Training and Testing (MITT) study area : programmatic report, April 2020
  • Description:
    Understanding the spatio-temporal movements of animals is an integral component of wildlife conservation and management. Marine turtles are species of conservation concern and satellite telemetry is a primary research tool used to study their movements, providing high accuracy location data in near “real time,” thus facilitating rapid identification of movements and key habitats. Although it has been recognized that both green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles inhabit the waters around Guam and the Commonwealth of the Northern Mariana Islands (collectively referred to as the Mariana Archipelago), their distribution and habitat use in the region remains unclear. In 2013, under an inter-agency agreement between the United States Navy and the National Oceanic and Atmospheric Administration (NOAA), NOAA began conducting in-water surveys to record and quantify observations of marine turtles around the Mariana Archipelago. When observed, attempts were made to hand-capture turtles and equip them with satellite tags in an effort to better understand their spatial ecology. 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. Movements and habitat use were highly neritic for the overwhelming majority of turtles, 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 more vagile movement patterns observed, including shifts in intra-island foraging areas (n = 7), transitions between inter-island foraging areas (n = 2), and a long-range migration departure out the Mariana Archipelago (n = 1). 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 research detailed in this report provides important insights into the movement ecology of green and hawksbill turtles around the Mariana Archipelago and represents the most rigorous individual satellite tracking study on these species in the world.
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