Abstract
Delineation of home ranges, residence and foraging areas, and migration corridors is important for understanding the habitat needs for a given species. Recently, many population segments of Northwest Atlantic loggerhead sea turtles (Caretta caretta) were designated as endangered or threatened; the smallest subpopulation is in the Dry Tortugas. Foraging and residence areas for this subpopulation have not been defined outside the Gulf of Mexico. Here, for Dry Tortugas loggerheads that traveled to the Bahamas, we use a combination of switching state-space modeling (SSM) and home-range estimators to determine migration period, spatially delineate and describe residence areas, and examine inter-annual home-range repeatability. In 5,973 tracking days, migration dates for Dry Tortugas loggerheads traveling to the Bahamas occurred during July–September, with turtles tracked twice showing remarkably similar migration paths and timing of departure from nesting sites. Core-use residence areas for 19 loggerheads ranged from 3.7 to 179.5 km2 (mean ± 1 SD = 56.2 ± 49.5 km2). For three turtles, we found inter-annual home-range repeatability, with centroids of core areas only 0.7–2.9 km apart and significant overlap of inter-annual 50% kernel contours. We demonstrate a previously unknown link between Dry Tortugas nesting beaches and Bahamas residence areas; 17/39 (43.6%) of nesting loggerheads tagged in and tracked from the Dry Tortugas take up residence at sites in the Bahamas. Residence area estimates for these turtles were similar in size to previous foraging area estimates for two turtles tracked to the Bahamas in other studies. We show inter-annual residence area repeatability, and that residence areas of different individuals generally did not overlap. We suggest that these loggerheads possibly establish territories.
Highlights
Delineation of home ranges, residence and foraging areas, and migration corridors is important for understanding the habitat needs for a given species
Turtle B had the same dates of migration for 8 of 15 total migration days; turtle E had the same dates of migration for 13 of 37 total migration days, turtle G had the same dates of migration for 3 of 10 total migration days, and turtle L had the same dates of migration for 13 of 27 total migration days
Female loggerheads traveling from Dry Tortugas (DRTO) to the Bahamas show a high level of repeatability in both migration corridors and residence area use, and a low amount of residence-area overlap with conspecifics, suggesting they may establish territories
Summary
Delineation of home ranges, residence and foraging areas, and migration corridors is important for understanding the habitat needs for a given species. Delineation of home ranges, residence and foraging areas, and migration corridors is essential to understand the spatial extent of habitats necessary for a given species. Defining these areas can be challenging in the marine environment given their often separate geographic locations, but electronic tags (i.e., satellite, GPS, and geolocation tags) have allowed delineation of high-use at-sea residence sites for marine megafauna, including sea turtles [1,2,3,4,5,6]. For loggerhead sea turtles locations of oceanic ‘hotspots’ representing key residence and foraging habitats have recently been delineated in the southeast US [11,22] and the Gulf of
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