Proceedings of the 19th Annual ISTS: sea turtle genetics

Black turtle (Chelonia mydas agassizii) foraging grounds along the coasts of Baja California, Mexico (Fig. 1) were surveyed during 1996-1998. 92 tissue samples were collected and analyzed using standard molecular genetic methods. Haplotypes from feeding areas were compared to those known from nesting populations in the eastern and central Pacific (Dutton et. al., unpublished data). Results suggest that Baja California’s Chelonia originate from several disparate nesting areas. The majority of the haplotypes found on foraging grounds are of the Michoacan type (80%), however approximately 20% were not.

Hypotheses for the origin of these turtles include dispersal from Hawaiian rookeries (6% were haplotype D; Dutton’s nomenclature) or the Islas Revillagigedos, a small archipelago off of the coast of Colima, Mexico. As genetic samples have not yet been obtained from the Islas Revillagigedos we recommend doing so. The hypothesized “Revillagigedos” haplotype (G; Dutton’s nomenclature) was significantly more abundant along the Pacific coast when compared to Gulf of California feeding grounds, supporting pelagic dispersal from the archipelago to the feeding grounds on the west coast of Baja California.

Supporting information from tagging and satellite telemetry reiterate the conclusion that a majority of Baja California Chelonia originate from and return to nest in Michoacan, Mexico. Three adult female turtles were tracked using satellite telemetry from Gulf of California feeding grounds to the vicinity of Colola, Michoacan. Each of the three turtles had “Michoacan” haplotypes (E,E, and N; Dutton’s nomenclature). All tag returns from Baja California feeding grounds have been from Colola or Maruata, Michoacan. None of the 250+ turtles tagged by this project have been found on any nesting beach other than those in Michoacan.

These results represent the first efforts to define management units for the east Pacific green turtle, a population that continues to decline despite nearly three decades of conservation efforts on its principal nesting beaches in Michaocan (Alvarado, pers. comm.). They also represent the first black turtles ever tracked from feeding to nesting areas, a distance of approximately 2000 km. Further, these results suggest that high mortality rates of large subadult and adult Chelonia on feeding grounds have likely played a significant role in the slow recovery of several eastern Pacific rookeries.