Antipredatory strategies of leatherback sea turtles during internesting intervals on St. Croix, US Virgin Islands

Abstract

Predators affect prey through mortality, and prey respond by employing antipredatory strategies. Although leatherback sea turtles Dermochelys coriacea are the largest sea turtle, they are susceptible to shark predation. Females lay multiple clutches of eggs separated by a ~10 d internesting interval at sea, during which they move many kilometers away from the nesting beach. The goal of this study was to test the hypothesis that this wide-ranging behavior was associated with predator avoidance. To accomplish this goal, we used animal-borne video and data recorders along with satellite telemetry to monitor diving behavior and track the at-sea movements of females during the internesting intervals on St. Croix, US Virgin Islands. After they departed the nesting beach, females immediately swam a mean maximum distance of 101 km from St. Croix. The mean transit distance during 10.19 d at sea was 466 km. We recorded 102 periods during which females inverted and rotated vigorously for an average of 2.7 min at or near the surface. Because females nesting on St. Croix commonly exhibit scars and fresh wounds, many of which result from shark encounters, this behavior likely represents a defensive response to predator attack. The frequency of defensive behaviors that occurred <6 km from the nesting beach (4.6 d-1) was 3.3-fold greater than when they were >6 km from shore (1.4 d-1). By moving offshore, females reduced the possibility of predator encounters by 53%.