Nesting Ecology of the Leatherback Turtle, Dermochelys coriacea, at Parque Nacional Marino Las Baulas, Costa Rica: 1988–1989 to 1999–2000
We collected data on nesting ecology and identified individual turtles that nested at Parque Nacional Las Baulas, Costa Rica, one of the few remaining nesting sites for Pacific leatherbacks, from 1988–1989 to 1999–2000. We tagged individual female turtles with flipper tags and later with Passive Integrated Transponder (PIT) tags that permitted permanent identification. During the full calendars years of 1990 and 1995, over 93% of nests were laid between the beginning of October and the end of February. We found that 92.4 ± 1% of nesting attempts resulted in successful oviposition, with a mean clutch size of 64.7 ± 1.4 yolked and 38.5 ± 1.0 yolkless eggs (n = 1389). Mean standard curved carapace length and curved carapace width during the surveyed years ranged from 144.4 ± 0.6 cm to 147.6 ± 0.3 cm and from 103.9 ± 0.3 cm to 105.5 ± 0.6 cm, respectively. Reproductive output as determined by estimated clutch frequency (ECF) ranged from 4.3 ± 0.2 to 7.9 ± 0.3 clutches per female per nesting season. The mean period between nesting seasons for an individual turtle was 3.7 ± 0.2 years; only 15% of turtles tagged in 1993/1994 returned to nest again within six years. The nesting population declined from 1367 adult females in 1988/1989 to 231 in 1999/2000. The decline in the nesting population was apparently because of the low incidence of turtles returning to nest in more than one season.Abstract
Monthly distribution of leatherback turtles nesting at Playa Grande and Playa Ventanas in Parque Nacional Las Baulas, Costa Rica from full-year body pit counts in 1990 and 1995. Bars show mean ± 1 SE
Representative data on emergence of nesting leatherback turtles at Playa Grande from December 1998 and January 1999 showing the time of observed turtle activity (solid black circles) and time of the high tide each night (black line). The high tide advances between 40 and 60 min per day dependent on the phase of the lunar cycle
Frequency distribution of the Observed Internesting Period (OIP) for leatherback turtles at Playa Grande during the 1997–1998 season
Number of nesting female leatherbacks and number of body pits at Playa Grande, Costa Rica from 1988–1989 to 1999–2000. We calculated numbers from 1988–1989 to 1992–1993 from nest counts and an ECF of 6.8 clutches per female. Error bars show error of minimum and maximum ECF from 1996–1997 to 1999–2000 (ECF 6.4–7.9). We determined numbers from 1993–1994 to 1999–2000 from actual numbers of female turtles tagged during the survey period and calculated for the full year from temporal distribution of nesting activity. Error bars from 1993–1994 to 1999–2000 show error in calculation of full-year total from subset of data collected from October to March each season. Body pit count error was calculated in the same manner