MTN 71:6-7 Results of the 1994 nesting season at chenkan, campeche, Mexico

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RESULTS OF THE 1994 NESTING SEASON AT CHENKAN, CAMPECHE, MEXICO

Introduction: The coast of Campeche, Mexico, at the southern limit of the Gulf of Mexico, is known to be one of the most important nesting areas for hawksbill turtles (Eretmochelys imbricata) in the world (Meylan, 1989). One of the more important sites, in terms of numbers of nests recorded, is Chenkán, which has been operating as a "campamento tortuguero" (sea turtle camp) since 1986. Both hawksbill and green (Chelonia mydas) turtles nest there (Barrios and Canul, 1993). During the 1994 nesting season, seven distinct turtle camps (including the one at Chenk†n) were set up on the Campeche coast, each administered by a different organization. The present report is a summary based on the work carried out at Chenkán (Sanchez et al., 1994).

Study Area: During the 1994 nesting season, the Chenkán camp was responsible for 20 km of coastline between Rancho Nohán and Puente Chenkán II (km 90 to km 110 on the Federal Highway Carmen-Campeche). Chenkán ("snake hole" in Maya) is located at km 101.5 on the Federal Highway, and the study area lies between 19°15'N, 90°10'W and 19°00'N, 90°50'W. The area is typified as hot, subhumid, with a mean annual air temperature of 26°C and annual average rainfall between 800-1500 mm, most of which falls during the summer (Garcia, 1974). The vegetation of the beach is dominated by coconut plantations (Cocus nucifera), which are now dying because of a virus. The Federal Highway runs roughly parallel to the coast, and in the Chenkán area it is generally within 100 m of the shoreline. Immediately inland of the highway is a vast mangrove forest and estuary.

Materials and Methods: Beach monitoring began on 1 April 1994 and continued until the end of August. In addition to foot patrol, beach transportation was provided by a 4-wheel all-terrain-vehicle (Honda) and a pickup truck. Each night, at about 2200 hr, one group of people would set out east along the beach, while the other group went west. Nesting females were tagged with monel cattle-ear tags provided by the Secretaria de Pesca; tagging and measuring of females was carried out after they nested. Eggs from most nests were transported to a beach hatchery at Chenkán. The eggs were placed in man-made nests with dimensions similar to natural nests. A week before the hatchlings were expected to emerge, the artificial nest was covered with a cylinder of wire mesh. Hatchlings were counted and released during the night or early morning, and nests were excavated (post-hatching) to quantify the contents. From January to September approximately 35 km of beach, from km 90 to km 125, were patrolled during morning hours to record stranded turtles. Carcasses were weighed and measured, and their physical condition was described.

Results: During the 1994 season, 76 nesting hawksbills were tagged; of these, 32 individuals were recaptured a total of 49 times. Of the 300 hawksbill nests reported, 238 were transplanted to the hatchery, 8 were moved to new sites on the beach, and 54 were left in situ. Nesting was recorded from 8 April to 23 August; the peak occurred in June, with 34% of the nests. More nests were laid during new and waxing moons. Out of a subsample of 230 nests, 126 (55%) were laid between km 106 and km 109; the densest nesting occurred between km 107 and km 108, with 55 nests (24% of the subsample).

Of the 238 transplanted nests, 68% were laid in habitat characterized as 'high beach with vegetation'. The average clutch size of the transplanted nests was 149.51 eggs, and the average number of hatchlings liberated from hatchery nests was 103.63, yielding an average hatch success of 69%. The average hatch success of in situ nests was estimated to be 74%, and nests moved to new sites on the beach had an estimated average hatch success of 53%.

A total of 50 hawksbills were found dead on the beach; 48 of them ranged in size from 17-55 cm in carapace length, with the two remaining turtles measuring 83 and 90 cm. One stranded green turtle was of juvenile size. Strandings were recorded from January to September, with a peak of 25 in May. Marks on the necks and heads of the cadavers indicated that they had been drowned in gill nets, which are commonly used in this region.

Acknowledgements: During the nesting season students from the Universidad Autónoma de Campeche and the Centro de Estudios Tecnológicos del Mar de Campeche collaborated with beach patrolling activities and took part in the release of hatchlings. Lic. Gabriel Sánchez Dzib helped with computer analysis, and Dr. J. Frazier with the preparation of this report.

Barrios S., R. and J. M. Canul V. 1993. Manejo de la zona del refugio de las tortugas marinas en Chenkán, Municipio de Champotón, Campeche, 1990, p.91-97. In: J. Frazier (Chief Editor), Memorias del IV Taller Regional Sobre Programas de Conservación de Tortugas Marinas en la Península Yucatán. Univ. Autónoma de Yucatán, Mérida.

Garcia, E. 1981. Modificaciones al sistema de clasificación climática de Kopen (3rd ed.) Offset Larios, México, D.F. 252 pp.

Meylan, A. B. 1989. Status report of the hawksbill turtle, p.89-94. In: L. Ogren (Chief Editor), Proc. Second Western Atlantic Turtle Symposium. NOAA Tech. Memo. NMFS-SEFC- 226. U. S. Dept. Commerce.

Sánchez A., M, A. del C. Paredes M., R. Barrios S., A. Contreras R., G. Sánchez Dzib and F. Alvarez R. 1994. Campamento Tortuguero "Chenkán" Campeche. Programa Nacional de Protección y Conservación Ecológica de las Tortugas Marinas, Temporada 94.Secretaría de Desarrollo Social; Dirección de Aprovechamiento Ecológico de los Recursos Naturales. Campeche, Campeche.

MANUEL SANCHEZ ARJONA, RAFAEL BARRIOS SANDOVAL, ADRIANA PAREDES MEDINA, ALBERTO CONTRERAS REJON and FERNANDO ALVAREZ RIVAS, Subdelegación de Medio Ambiente, Secretaría del Medio Ambiente, Recursos Naturales y Pesca, Av. 16 de septiembre s/n, 2° piso, Palacio Federal, Col. Centro, Ciudad de Campeche, Campeche C.P. 24000 MEXICO.