Diving Behavior Of Hawksbills Sea Turtles

Coral Reefs (1997) 16: 133—138

Diving behavior of immature hawksbill turtles (Eretmochelys imbricata) in a caribbean reef habitat
R. P. van Dam*, C. E. Diez
University of Amsterdam, Institute for Systematics and Population Biology, P.O. Box 94766, 1090 GT Amsterdam, The Netherlands Department of Biological Sciences, University of Central Florida, Orlando, Florida, 32816—2368, USAAccepted: 2 July 1996

Abstract. Time-depth recorders were deployed on immature hawksbill turtles at the southwestern reefs of Mona Island, Puerto Rico, to examine patterns of diving behavior. Diving profiles of 10—12 day duration were obtained from five turtles ranging in carapace length from 27—52 cm. Turtles exhibited contrasting diurnal and nocturnal diving behaviors. During daylight hours, diveswere made 92% of the time, featured continuous depth variation and were attributed to foraging activity. Foraging dive duration increased with turtle size; individual mean dive durations ranged from 19—26 min; mean post-dive surface intervals ranged from 37—64 s; mean depths ranged from 8—10 m. At night, dives were made 86% of the time to constant depths and were interpreted as resting behavior.Resting dive durations were not dependent on turtle size; individual mean dive durations ranged from 35—47 min; mean post-dive surface intervals ranged from 36—60 s; and mean depths from 7—10 m. Immature hawksbill turtles maintained short term home ranges several hundred meters in extension.

Caribbean they appear to be primarily spongivorous (Meylan 1988). Although the terrestrial nesting behaviorof Eretmochelys has been described in detail (Deraniyagala 1939; Carr et al. 1966), few accounts of the at-sea behavior of the species are available. One report by Hirth et al. (1992) describes immature hawksbill turtles swimming and resting at a fringing reef in Papua New Guinea. In this study, we document the diving behavior observed in immature hawksbill turtles at a reef site in the northernCaribbean. We compare the behavior of this species with that of the more extensively studied green turtle (Chelonia mydas), which has distribution and habitat preferences comparable to those of the hawksbill turtle. Study area and methods Data were collected during the 1992 to 1994 field seasons (July—November) in a study area along the southwestern coast (18°05N, 67°57W) of Mona Island, PuertoRico (Fig. 1). The study area was divided into three sections named according to the adjacent beaches: Sardinera, Mujeres, Carabinero. All sections lie on the leeward side of the island and are thus relatively protected from prevailing winds and associated waves from the east and southeast. However, the reef profile and benthic composition of the areas are substantially different. The Sardinera areaconsists of a forereef with spurs and grooves at between 5 and 12 m depth, radiating outwards from a fringing reef. The reef spur structures seldom reach more than 1.5 m above the substrate. Cover at 10 m depth is dominated by macro-algae, scleractinians, plexaurids and other gorgonians. Beyond 12 m depth, about 500 m offshore, the spur-groove system breaks up into large coral patches surrounded bysand. At Mujeres, the reef patches at 4 to 18 m depth are better developed, with typical structure heights of 1 to 2 m (up to 4 m) and overhangs and ledges providing turtles with ample shelter. Patches are covered with macro-algae, hydrocorals, scleractinians, gorgonians, and the prominent encrusting sponge Anthosigmella varians. At Carabinero, a hard-bottom terrace

Introduction The hawksbillturtle (Eretmochelys imbricata) is circumtropically distributed and frequently associated with coral reefs (Marquez 1990). Juvenile turtles with a carapace ´ length of 20 cm and larger are thought to take up residency in hard-bottom neritic habitats after completing a pelagic post-hatching life phase (Carr et al. 1966). Adaptations to hard-bottom environments include thick, abrasion resistant...