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Marine Turtle Newsletter 57:15-17, © 1992

1991 a 'Record Year' for Leatherback Productivity on St. Croix, U. S. Virgin Islands

Peter Dutton¹, Donna McDonald¹ and Ralf Boulon^2
1Leatherback Turtle Research and Conservation Project,
P. O. Box 1697, Frederiksted, St. Croix, USVI 00841-1697;
²Division of Fish and Wildlife, 101 Estate Nazareth, St. Thomas, USVI 00802

With regard to clutch frequency, and thus the output of hatchlings, 1991 was the most productive year on record for leatherback sea turtles nesting on the 2.4 km beach at Sandy Point National Wildlife Refuge, St. Croix (Figure 1). The 1991 total of 260 nests was the highest since the project's inception in 1982 (Table 1), but the number of turtles involved was lower than in other peak years (Figure 2). In 1991, as in previous years, the beach was patrolled nightly and all turtles (n=39) were observed and tagged. There were 16 remigrants: one first tagged in 1981, two in 1982, two in 1985, one in 1987, six in 1988, and four in 1989 (one of these was tagged at Manchineel Bay, St. Croix). One of the untagged turtles had a tag scar and thus may also have been a remigrant. Of the known remigrants, eight appear to be nesting on 2-yr cycles and eight on 3-yr cycles. Observed clutch frequency (observed nests per female) ranged from 1-11 (mean= 6.0, sd=2.55) in 1991. If we assume that undocumented nests were laid when an internesting interval was double or triple the usual 8-12 days, the mean number of nests per female can be estimated at 6.7 (sd=2.64). Mean observed clutch frequency was similar to that reported in 1990, but exceeded means calculated in previous years (Figure 3). We can only speculate as to the cause(s) for the increase in productivity; demographic and environmental factors may be involved. Perhaps food was more abundant in recent years, enabling females to reach a better reproductive condition. Record nesting on Culebra, Puerto Rico, in 1991 (T. Tallevast, pers. comm.) suggests that this trend may be more widespread, though data on individual fecundity are not available at that site. Our data emphasize the value of population studies and indicate caution when attempting to extrapolate population size from nest counts. More nests do not necessarily mean more turtles!

Figure 1. Total annual hatchling production from nests laid by leatherback sea turtles at Sandy Point National Wildlife Refuge, St. Croix, U. S. Virgin Islands, 1982-1991.

Table 1. Final outcome of leatherback sea turtle nests laid at Sandy Point National Wildlife Refuge, St. Croix, U. S. Virgin Islands, 1982-1991. Data were summarized from annual project reports submitted by Principal Investigators Scott and Karen Eckert (1982-1985), Robert Brandner and Susan Basford (1986-1990), and Peter Dutton and Donna McDonald (1991).

Figure 2. The number of adult female leatherback turtles nesting annually at Sandy Point, 1981-1991.

Figure 3. Observed and estimated nest frequency at Sandy Point, 1982-1991. Estimates for 1986-1990 not available.