The ecology and migrations of sea turtles. 7, The West Caribbean green turtle colony. Bulletin of the AMNH ; v. 162, article 1

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New York : American Museum of Natural History
"The present report is a summary and preliminary analysis of data on the green turtle, Chelonia mydas, that has been collected during a 22-year tagging program at Tortuguero, Costa Rica, 52 miles north of the Caribbean city of Puerto Limon. It is the first general account of Tortuguero results since 1960. From 1955 through the 1976 season, approximately 12,000 female green turtles have been tagged on the nesting beach. Of these, 2522 have been seen in subsequent years; 1412 of them as return migrants and 1110 on distant forage grounds or in migration. No turtle tagged at Tortuguero has ever been reported from any other nesting shore. The paper is concerned mainly with the migratory and behavioral ecology of the colony and with interseasonal changes in the nesting population. Results are presented in five sections, as follows: (1) Migratory geography and speed of travel: of 1110 long-distance, postseasonal recoveries of Tortuguero tags 957 have come from the Miskito Cays and adjacent parts of Miskito Bank off the Nicaraguan coast. Smaller numbers of recoveries cluster in Colombia, Panama, and Mexico. Analysis of monthly recovery frequencies in Nicaragua, and of periods of time elapsed between tagging and recapture, reinforce the assumption that Miskito Bank is a resident foraging range and not merely a travel station. Migratory travel speeds based on tag recoveries are compared with those recorded in the literature. (2)Nesting and renesting: The average number of nestings by a Tortuguero turtle during a season at the breeding shore is 2.8; the recorded maximum is seven, although eight probably occur occasionally. There is evidence that one-time nestings are a regular occurrence. The average renesting interval is 12.1 days. Remigrant turtles were found to nest more often than recruits. (3) Remigration: Of 1412 turtles that have returned to Tortuguero after previous appearances there, only six came back the following season. Interval percentages for the three predominant remigration periods are: two years, 21 percent; three years, 49 percent; four years, 18 percent. A unique contribution of the report is an extensive record of remigratory cycle-shifts, and tables showing composition of the nesting colonies of 1962-1972 with respect to past and future remigration-interval frequencies. (4) Reproductive homing: A distinction is made between philopatry, or regional return, and site fixity--the tendency to nest repeatedly on the same beach section within the home region. These two surely involve different cues; and the responses mediating open-sea orientation must be different from both. (5) Size of the West Caribbean population: A calculation of the number of sexually mature green turtles in the western Caribbean is made. An equation that takes into consideration the different proportions of two-, three-, and four-year remigratory periods is used to convert nesting arrivals into total female population. Since the latter varies from year to year, the average for the last six years is used in the calculation, and the resulting figure is doubled, on the assumption that there is a 1:1 sex ratio. The resulting total of mature green turtles in the population is 62,532. In the final section, the future outlook for the population is assessed and the need for further research in its shifting habitats, particularly the internesting habitat, is pointed out. The critical importance of developing an excluder device to keep sea turtles out of shrimp trawls is discussed"--P. 5.
46 p. : ill., map ; 26 cm.
Includes bibliographical references (p. 43-46).