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Marine Turtle Newsletter 63:6-7, © 1993

Reproductive Biology of Hawksbills Nesting in Antigua

James I. Richardson
Georgia Sea Turtle Cooperative, Institute of Ecology, University of Georgia
Athens, Georgia 30602-2968 USA

The Jumby Bay Hawksbill Project has completed six years (1987-1992) of intensive tagging with adult female hawksbill sea turtles (Eretmochelys imbricata) nesting at Pasture Bay, Long Island, Antigua (Eastern Caribbean). The results have recently been published by Hoyle and Richardson (1993). Pasture Bay is a natural beach of calcareous sand, with a community of mixed tropical hardwood trees and shrubs providing suitable nesting habitat. The beach (160 m in length) is foot-patrolled by a team of two biologists on hourly intervals from dusk until dawn during the 150-day principle nesting season (15 June - 15 November). The purpose is to record the activity and identity of each turtle on every nesting visit. The number of such events that are missed by the patrol team is less than 5% of total nesting activities each year. Loss of individual flipper tags is estimated at 5-10% over a 2-year or 3-year period. Turtles are protected from unnecessary harassment arising from research or other interpretative activities. The nesting beach is owned and managed by Jumby Bay Club and Resort. The research program is directed by the Georgia Sea Turtle Cooperative.

Ninety-one individuals have been tagged to date. The number of females nesting each season has ranged from 22 to 38 individuals. The proportion of untagged turtles during each of the last two seasons (1991-1992) has held relatively constant at less than 20%. Thus, annual recruitment to the nesting population can be not greater than 20% and is probably less by some number of turtles on longer remigration intervals and by possible tag loss. Turtles usually return on 2-year and 3-year remigration intervals, with a mean (n=51) of 2.53 years. Nine of 60 individuals (15%) have not returned in four years, and this represents potential bias for the remigration interval reported. The calculation of annual survivorship is difficult and perhaps premature with a short-term tagging study of six years, but best minimum estimates to date range from 0.98 (1987 turtles) to 0.89 (1988 turtles). Annual survivorship values are expected to increase with additional years of tagging data and improved tagging methods.

Individual turtles lay 4.52 clutches of eggs per season, with five clutches being the dominant mode. Mean clutch size is 157 eggs. An individual turtle will lay approximately 700 eggs per nesting season or 280 eggs per year of it's reproductive life (remembering that a turtle does not nest every year). The mean inter-nesting interval is 14.8 days (n=489), with some evidence that the first interval (15.2 days) is longer than the remaining intervals (14.4 days). The average nesting season, derived from a sample of 716 nests, describes a clear peak of activity in late August and early September. There is apparent bi-weekly periodicity in nesting activity that may even be synchronized across nesting seasons. Social facilitation has not been ruled out. Most females exhibit a propensity for arriving each nesting season on a date predictable for the individual, suggesting the existence of an accurate biological clock that coordinates the behavior of each turtle and defines the shape of the nesting season.

There have been 716 nests recorded for the six seasons, or a mean of 119 nests per survey season (15 June - 15 November). Since some minimal nesting occurs in every month of the year, an additional 20% of this value (±150 clutches) may represent nesting activity outside of the survey season. Mean hatching success has been above 80%. An estimated 100,000 hatchlings were produced from 1987-1992, speaking to the importance of Pasture Bay as a nesting beach for the endangered hawksbill in the Caribbean Sea. The Jumby Bay Club and Resort and the Georgia Sea Turtle Cooperative are working together to see that the future for the Pasture Bay hawksbills is secure. In addition to ongoing efforts to gather important population data on the nesting females, attempts are being made to improve nesting habitat at the site. A comprehensive national recovery action plan for sea turtles in Antigua and Barbuda (Fuller et al., 1992), recently developed by WIDECAST and published by the United Nations Environment Programme, highlights the significant work done at Pasture Bay and provides an integrated framework for continued work there.

Fuller, J. E., K. L. Eckert, and J. I. Richardson. 1992. WIDECAST Sea Turtle Recovery Action Plan for Antigua and Barbuda (K. L. Eckert, Editor). CEP Tech. Rept. No. 16. UNEP Caribbean Environment Programme, Kingston, Jamaica. 88 p.

Hoyle, M. and J. I. Richardson. 1993. The Jumby Bay Hawksbill Project: Survivorship, Mortality, Recruitment and Reproductive Biology and Behavior of Adult Female Hawksbill Sea Turtles (Eretmochelys imbricata) Nesting at Pasture Bay, Long Island, Antigua, 1987-1992. Technical Report. The Georgia Sea Turtle Cooperative, Institute of Ecology, University of Georgia, Athens. 76 p.