Leatherback Turtles (Dermochelys coriacea) on St. Croix, U.S. Virgin Islands: Fifteen Years of Conservation
– Ralf H. Boulon, Jr., Peter H. Dutton, and Donna L. McDonald
ABSTRACT - From 1981 to 1995, saturation tagging and consistent night patrols have yielded comprehensive information on every leatherback turtle (Dermochelys coriacea) nesting at Sandy Point National Wildlife Refuge, St. Croix, USVI. A total of 358 individual leatherbacks have been flipper-tagged, with 18 to 55 individual females per season. Annual remigration rates averaged 34.1%, and the most common remigration interval was two years. Turtles ranged in carapace length from 131.0 to 177.4 cm and in weight from 259 to 506 kg. The nesting period extends from 9 February to 11 August with each turtle laying an average of 5.26 nests per season with an internesting interval of 9.6 days. Clutch size averages 79.7 yolked eggs and 36.4 yolkless eggs. Incubation takes an average of 63.2 days with an in situ nest hatch success of 67.1% and a relocated nest hatch success of 60.4%. A few turtles encountered on Sandy Point were originally tagged on other beaches on St. Croix or on various beaches in Puerto Rico, including Culebra. Several turtles originally tagged on Sandy Point were later observed to nest at Vieques, Culebra, and Anguilla. One turtle stranded in New Jersey and another was caught in Mexico. Nearly half of the nests on Sandy Point were relocated to prevent loss due to predictable annual cycles of sand erosion and redeposition. Conservation efforts have reduced nest loss due to erosion to less than 5% and eliminated poaching of nests. We estimate that approximately 130,200 hatchlings emerged at Sandy Point from 1982 to 1995, possibly double the number that would have been produced without these efforts.

Nesting of the Leatherback Turtle (Dermochelys coriacea) in Tongaland, KwaZulu-Natal, South Africa, 1963-1995
– George R. Hughes
ABSTRACT - A modest nesting population of leatherback turtles has been vigorously protected and studied on the Tongaland coast of KwaZulu-Natal, South Africa, for 32 years from 1963 to 1995. The number of nesting females has grown significantly from about 20 nesting females per season to over 100 per season. Of 1329 females tagged, 1017 (76.5%) have never been identified again, though many untagged turtles have calluses suggesting high tag loss. Remigration rates averaged 30.5% for 1964-84, and 33.7% for 1984-95. The longest observed reproductive lifetime was 18 years and many females were recorded nesting over a period of more than 9 years. Re-nesting occurred most frequently at two year intervals (44.8%) and often at three year intervals (29.2%). However, most females appear capable of changing their remigration intervals quite frequently, even nesting occasionally in consecutive years (1.9%). Mean carapace length of the nesting females has decreased from 162.2 cm in 1964-68 to 159.6 cm in 1994-95. Long distance recoveries of females have been relatively few in number, and none have been recorded nesting elsewhere. This nesting population is now the focus for a successful tourism activity.

Leatherback Turtle, Dermochelys coriacea, Nesting and Nest Success at Tortuguero, Costa Rica, in 1990-1991
– Alison J. Leslie, David N. Penick, James R. Spotila, and Frank V. Paladino
ABSTRACT - Leatherback turtle nesting at Tortuguero, Costa Rica, in 1990 and 1991 took place from early March to early July and peaked in April for both years. We tagged 33 turtles in 1990 and 45 in 1991. Mean mass of 22 female turtles was 346.8 kg. Mean standard curved carapace length was 156.2 cm. Mean clutch size was 86 yolked and 53 yolkless eggs in 1990 and 80 yolked and 33 yolkless eggs in 1991. Mean mass of 613 yolked eggs was 84.3 g and mean diameter was 54.0 mm. In 1990, hatchlings emerged from 26 of 56 nests (46.4%). Poachers removed 14 clutches (25%), predators (dogs) destroyed 6 (10.7%), and tides and waves destroyed 10 (17.8%). Mean percent emergence for successful nests was 70.0%. In 1991, hatchlings emerged from 85 of 150 nests (56.7%). Poachers removed 17 clutches (11.3%), predators (dogs) destroyed 10 (6.7%), roots and debris destroyed 7 (4.7%), and tides and waves destroyed 31 (20.6%). Mean percent emergence for successful nests was 53.2%. Dogs destroyed an additional 40 (47.1%) of the 85 successful nests at emergence in 1991. Thus, 50 (33.3%) of the total number of nests studied in 1991 were destroyed by dogs. Poaching and predation were related to nest position on the beach, being highest in the mid- and upper beach zones. Soil temperature profiles predicted that both nesting seasons produced predominantly male hatchlings; 54% male in 1990 and 62% male in 1991. However, when we added the effect of metabolic heating, the sex ratio predictions went to 70.8% female in 1990 and 63% female in 1991. Rainfall had a profound cooling effect on incubation (sand) temperatures with mean sand temperature of 28.5oC in 1990 and 29.0oC in 1991. Water potential values of beach sand ranged from -1.5 to -8.5kPa. An estimated 150-368 females nested at the Tortuguero beach.

Leatherback Turtle, Dermochelys coriacea, Nesting at Tortuguero, Costa Rica, in 1995
– Cathi L. Campbell, Cynthia J. Lageux, and Jeanne A. Mortimer
ABSTRACT - We monitored leatherback turtle, Dermochelys coriacea, nesting in Parque Nacional Tortuguero on the Caribbean coast of Costa Rica during the 1995 nesting season. Between 8 April and 11 May, leatherbacks deposited an estimated 702 clutches along 35 km of beach between the mouths of the Tortuguero and Parismina rivers. Comparison of our data with those from previous studies indicate a probable decline in numbers of nesting turtles, possibly caused by the high levels of egg harvest which have occurred during recent decades. Public awareness campaigns and programs to encourage community participation in conservation efforts are needed in addition to more stringent enforcement of existing laws protecting leatherback turtles and their eggs. We advocate that ground surveys of the nesting beach be conducted throughout the nesting season complemented by occasional aerial surveys of the entire coastline to assess overall distribution of nesting leatherbacks.

Nesting Leatherback Turtles at Las Baulas National Park, Costa Rica
– Anthony C. Steyermark Kristina Williams, James R. Spotila, Frank V. Paladino, David C. Rostal, Stephen J. Morreale, Maria Teresa Koberg, and Randall Arauz
ABSTRACT - Las Baulas National Park on the Pacific coast of Costa Rica includes three beaches, Playa Grande, Playa Langosta, and Playa Ventanas, that support a major nesting colony of leatherback turtles, Dermochelys coriacea. During the 1993-94 nesting season, we tagged 159 individuals with inconel tags, and 154 of these with PIT tags also. During the 1994-95 season, we tagged 462 individuals with inconel tags, and 459 of these with PIT tags also. Documented inconel flipper tag loss (10%, 1993-94; 7.4%, 1994-95) was high given the short time span of this study (November to February). In contrast, apparent loss rate of PIT tags was 3.1% in 1993-94 and 3.3% in 1994-95. Las Baulas leatherbacks were smaller than leatherbacks reported from nesting beaches outside the east Pacific area. Mean standard curved carapace length (SCCL) was 144.4 cm in 1993-94 and 147.6 cm in 1994-95. Modal internesting period was 9 days. Mean observed clutch frequency was 3.6 for the 1993-94 season and 3.5 for the 1994-95 season. Mean estimated clutch frequency was 5.1 for 1993-94 season and 4.9 for the 1994-95 season. Estimated clutch frequency was higher than observed for both seasons due to incomplete beach coverage and possibly to lack of beach philopatry. An estimated 1600 leatherbacks previously nested at Playa Grande during each of the 1988-89 and 1989-90 seasons. We estimated 202 nesting leatherbacks in 1993-94 and 469 in 1994-95. The decline in the 1993-94 season and the ensuing increase in 1994-95 in numbers of leatherbacks at Las Baulas was correlated with changes in mean sea surface temperatures in the equatorial Pacific Ocean region (El Niño). The decline in numbers of leatherbacks at Las Baulas since the high years of 1988-89 may be due to the recent increase in development in the area surrounding nesting beaches, as well as incidental catch of leatherbacks in offshore fisheries.

Subsistence Hunting of Leatherback Turtles, Dermochelys coriacea, in the Kai Islands, Indonesia
– Alexis Suarez and Christopher H. Starbird
ABSTRACT - The subsistence hunting of the leatherback sea turtle (Dermochelys coriacea) in the Kai Islands, Indonesia, was studied during October - November 1994. This traditional fishery has been part of Kai culture for centuries and encompasses ancient beliefs and rituals of adat which are equated with the will of the ancestors. Peoples of eight villages hunt leatherbacks in the open sea using traditional dugout sailboats and harpoons during the oceanic calm period of October to February. Leatherback hunts were observed and interviews were conducted with village chiefs, elders, and fishermen from ten villages in the Kai Islands. Capture numbers, locations, methods, and traditional beliefs and rituals associated with hunting leatherbacks are described. The loss of traditional restraints on hunting is the greatest threat to this population of leatherbacks. In addition to being hunted for ritual purposes as in past generations, leatherbacks are currently also taken regularly for sustenance.

Decline of the Leatherback Population in Terengganu, Malaysia, 1956-1995
– Eng-Heng Chan and Hock-Chark Liew
ABSTRACT - The Rantau Abang leatherback population in Terengganu, Malaysia is now severely depleted, with current nestings representing less than 1% of levels recorded in the 1950s. Major causes of decline are mortalities attributed to fisheries operations in the high seas as well as within the territorial waters of Malaysia, and a long history of egg exploitation. These problems have been compounded by loss of suitable nesting habitat due to tourism-related development, marine pollution, and sub-optimal hatchery practices leading to reduced hatch rates and sex-biased hatchling production. The global moratorium on driftnet fisheries and complete protection of eggs to ensure optimal hatch rates and production of hatchlings with balanced sex ratios offer some hope for the eventual rehabilitation of the depleted population.

Leatherback Turtles, Dermochelys coriacea, Nesting in French Guiana, 1978-1995
– Marc Girondot and Jacques Fretey
ABSTRACT - Ya:lima:po beach in French Guiana exhibits the highest concentration of leatherback (Dermochelys coriacea) nesting in the world. Scientists and volunteers from more than 25 countries have worked within the Kawana marine turtle project for 16 years. Numbering and tagging of leatherbacks has been the main activity of this project. Number of nests per year has been estimated for 13 nesting seasons between 1978 and 1995. More than 50 thousand nestings were recorded annually in 1988 and 1992, but only 10 to 15 thousand annually in 1978-86, 1993, and 1995, with intermediate numbers of 20 to 30 thousand annually in 1987, 1989, 1991, and 1994. A general increase in the number of nests has been observed in the last few years as compared to the first years, but the actual trend is unclear. Analysis of the database of tagged leatherbacks (over 31,000 data points) elucidates behavior of this species within and between nesting seasons.

Worlwide Population Decline of Dermochelys coriacea: Are Leatherback Turtles Going Extinct?
– James R. Spotila, Arthur E. Dunham, Alison J. Leslie, Anthony C. Steyermark, Pamela T. Plotkin, and Frank V. Paladino
ABSTRACT - We estimated the number of leatherbacks, Dermochelys coriacea, nesting on 28 beaches throughout the world from the literature and from communications with investigators studying those beaches. The estimated worldwide population of leatherbacks in 1995 was about 34,500 females on these beaches with a lower limit of about 26,200 and an upper limit of about 42,900. This is less than one third the 1980 estimate of 115,000. Leatherbacks are rare in the Indian Ocean and in very low numbers in the western Pacific Ocean. The largest population is in the western Atlantic. We used an age-based demographic model to answer "what if?" questions about the stability of leatherback populations. We formulated a hypothetical life table model based on estimated ages of sexual maturity at 5 or 15 years. Leatherbacks that mature in 5 years would exhibit much greater population fluctuations in response to external factors than would turtles that mature in 15 years. Simulations indicated that leatherbacks would maintain a stable population only if both juvenile and adult survivorship remained high. If other life stages (egg, hatchling, juvenile) remain static, stable leatherback populations could not withstand an increase in adult mortality above natural background levels without decreasing. However, protection of eggs during incubation and hatchlings during their first day of life (potentially doubling survival) could have a significant effect on overall stability of leatherback populations in the face of an increase in adult mortality. Leatherback populations in the Indian Ocean and western Pacific Ocean cannot withstand even moderate levels of adult mortality. Even the Atlantic populations are being exploited at a rate that cannot be sustained. Leatherbacks are on the road to extinction and further population declines can be expected unless we take action to reduce adult mortality and increase survival of eggs and hatchlings.

 Read the entire article 

Shallow Water Diving by Leatherback Turtles in the South China Sea
– Scott A. Eckert, Hock-Chark Liew, Karen L. Eckert, and Eng-Hang Chan
ABSTRACT - Internesting dive behavior of 3 leatherback turtles near Rantau Abang, Malaysia, is presented. Diving patterns were similar to leatherbacks in the Caribbean in that there was almost no period when the turtles were not diving, and dives were influenced by time of day. Daytime dives were longer, deeper, and had longer post-dive surface intervals than night-time dives. Bottom durations were also longer during the day. Major differences between Caribbean and Malaysian leatherbacks were the depth and duration of the dives. Malaysian turtles were constrained by the shallow waters of the South China Sea to dives of less than 60 m, and indeed many of their dives appeared to be to the bottom. Dive durations were much longer for Malaysian turtles. We suggest that this may be due to a lower metabolic demand of diving by Malaysian turtles, possibly because they were resting on or near the bottom on each dive. Bottom times were greater than 3 minutes in 47% of all dives, which is distinctly different than Caribbean leatherback diving. There was a strong correlation between dive depth and dive duration but only a weak relationship (if any) between dive duration and bottom time and none between dive duration and post-dive surface time.