Biology

 

Description

The East Pacific green turtle is distinguished from the green turtle mainly by size, coloration and carapace shape. The carapace of the adult East Pacific green turtle is narrower, more strongly vaulted and more indented over the rear flippers than that of the green turtle (Cornelius 1986; Márquez 1990). The East Pacific green turtle is also conspicuously smaller and lighter than the green turtle. In the rookeries of Michoacán, Mexico, the mean size for nesting females is 82.0 cm in curved carapace length (CCL) (range 60.0-102, n=718) (Alvarado and Figueroa 1990). On the Galapagos Islands, the mean CCL for nesting females is 80.0 cm (range 74.0-100) (Márquez 1990). The mean straight carapace length (SCL) of nesting females at Playa Naranjo, Costa Rica is 82.9 cm (range 73.0-97.0, n=73) (Cornelius 1976). Adult females weigh between 65 – 125 kgs (Cornelius 1986). Adult males in the rookeries of Mexico are smaller than females with an average CCL of 77.0 cm (range 71.0-85.0, n=32) (Figueroa 1989). Mean hatchling length in Michoacán is 4.5 cm in SCL (range 4.2-5.0, n=140) (Zamora 1990).

In adult East Pacific green turtles, the carapace and dorsal surfaces of the head and flippers are olive-green to dark gray or black, while the plastron varies from whitish-grey to bluish or olive-grey. Considerable gray pigment often infuses the plastron. Hatchlings are black to dark grey above and white below with a white border around the dorsal edge of the carapace and flippers. Young juveniles are usually brightly colored with a mottled or radiating carapacial pattern of light and dark brown, reddish brown, olive and yellow (Caldwell 1962).

Taxonomy

The generic name Chelonia was introduced by Brongniart (1800). The specific name mydas was first used by Linnaeus (1758). The genus Chelonia is often considered to include the single species C. mydas with two distinct subspecies recognized: the East Pacific green turtle C. m. agassizii (Bocourt 1868) in the eastern Pacific (from Baja California south to Peru and west to the Galapagos Islands) and the green turtle C. m. mydas (Linnaeus 1758) in the rest of the global range (Groombridge and Luxmoore 1989). Nevertheless, there has been some controversy over the taxonomic status of the East Pacific green turtle. The nesting populations of the east Pacific differ from other forms of mydas in size, coloration, carapace shape (Cornelius 1986; Groombridge and Luxmoore 1989), as well as in osteological features (Kamezaki and Matsui 1995). Nuclear DNA analysis of Chelonia populations showed that samples from the Pacific coast of Mexico and the Galapagos Islands were closely associated and fairly remote from other populations (Karl et al. 1992), however, mitochondrial DNA (mtDNA) analyses of the global C. mydas complex do not support the genetic distinctness of the East Pacific green turtle from Chelonia populations in other regions of the world (Bowen et al. 1992; Dutton et al. 1996). It is clear that the question of species status must ultimately be resolved by taking into account morphometric, genetic and behavioral aspects. In the absence of a thorough study of the morphology and genetics of the agassizii form, set in the context of the overall systematics of the C. mydas group, the East Pacific green turtle is considered to be a melanistic form of Chelonia mydas of the monotypic genus Chelonia for the purpose of this recovery plan.

Regardless of taxonomic designation ultimately conferred upon the melanistic form, the remaining large nesting populations of Chelonia in the east Pacific should be managed as distinct population units. This document presents an agenda for the recovery of these regionally distinct and important populations.

Geographic Scope

Defining the geographic range of a population of sea turtles in the Pacific Ocean is difficult. Sea turtles are highly migratory, and the life histories of all species exhibit complex movements and migrations through geographically disparate habitats. Because the U.S. Pacific Sea Turtle Recovery Team is required to focus on sea turtle populations that reside within U.S. jurisdiction, we must delineate what constitutes a population where individuals reside permanently or temporarily within U.S. jurisdiction and what actions must be taken to restore that population. This has proven to be quite challenging because sea turtles do not recognize arbitrary national boundaries and in most cases we have only limited data on stock ranges and movements of the various populations. In this recovery plan we have tried to make these judgements with the best information available, and to suggest means by which the United States can promote population recovery.

Geographic scope (from a U.S. jurisdictional perspective) for all six of the U.S. Pacific sea turtle recovery plans (written for five species and one regionally important population) is defined as follows: in the eastern Pacific, the west coast of the continental United States (Figure 1a); in the central Pacific, the state of Hawaii and the unincorporated U.S. territories of Howland, Baker, Wake, Jarvis, and Midway Islands, Johnston Atoll, Palmyra Atoll, and Kingman Reef; in Oceania, Guam, the Commonwealth of the Northern Mariana Islands (CNMI), and American Samoa (see Figure 1b). The U.S.-affiliated but independent nations of the Republic of the Marshall Islands (RMI), Federated States of Micronesia (FSM), and the Republic of Palau are also included. The FSM includes the states of Yap, Pohnpei, Chuuk, and Kosrae. While independent, all retain clearly defined administrative links to the United States in the areas of defense, natural resource management, and some regulatory issues. Thus, we include them here in an advisory capacity. Finally, where eastern Pacific sea turtles are held in common with Mexico, discussion of the status and recovery of these stocks will also include discussion of the resource under Mexican jurisdiction.

In all cases where U.S. sea turtle stocks are held in common with other sovereign states, we have tried to suggest means by which the United States can support efforts at management of those stocks by those states. We recognize that other nations may have different priorities than the United States and we have sincerely attempted to avoid establishing policy for those nations.
Because of the highly migratory behavior of adult turtles, and the likelihood of shifting habitat requirements of post-hatchlings and juveniles, the populations of East Pacific green turtles, Chelonia mydas, in the Pacific Ocean cross international boundaries.

The west coasts of Central America, Mexico and the United States constitute a shared habitat for East Pacific green turtles. The following discussions acknowledge the extended range of East Pacific green turtles by incorporating relevant biological information from within and without U.S. political jurisdiction.

Occurrence Records

Drawing on the records in the Global Biodiversity Information Facility (GBIF), we can see where green sea turtles have been found: