The Feeding Ecology of the West Caribbean Green Turtle (Chelonia mydas) in Nicaragua

Abstract

The stomach contents of 243 subadult and adult green turtles, Chelonia mydas, taken at their foraging grounds off the eastern coast of Nicaragua, were examined. The sex and site of capture of most of the turtles were known. Turtle grass, Thalassia testudinum, accounted for an average of 78.9 percent of the dry weight of the samples. The turtles were found to graze at the bases of the Thalassia plants where they obtained the youngest growth. They avoided those blades which were encrusted with epiphytic animals and plants. In decreasing order of abundance, the remaining food items comprised: other species of seagrasses (9.7%), algae (8.2%), benthic substrate (1.8%), and animal matter (1.4%). In the northern part of the Nicaraguan foraging range Thalassia accounted for nearly 90 percent of the diet, while in the more southerly portions fleshy red algae predominated. Turtles migrating between the feeding and nesting grounds travel near shore, at which time they consume greater amounts of Syringodium filiforme, red algae, and highly lignified terrestrial debris deposited at river mouths. No difference in the diets of the two sexes was recorded. THE AIM OF THIS STUDY is to enhance our generally limited knowledge of the ecology of the green turtle, Chelonia mydas, at its feeding grounds. Information obtained by tagging nesting females has made it possible to piece together migratory routes, the location of feeding grounds, and the time intervals between nestings. Virtually nothing, however, is known of the ecology of the animals away from the nesting beach. The green turtle colony that nests at Tortuguero, Costa Rica, is both the largest in the western Caribbean and the best studied in the world. Here, a tagging project conducted by Archie F. Carr, Jr. has been in progress for 27 years. At Tortuguero, females nest at intervals of two, three, and four years, with longer cycles possibly occurring. After laying between one and six clutches of eggs during a given nesting season, the females travel to their distant feeding grounds, and apparently remain there until the time again comes to migrate to Tortuguero (Carr et al. 1978). Because it has not been feasible to tag males, their movements remain unknown. However, it is assumed that they too return to the same feeding grounds after mating off the nesting beach. It has been postulated that conditions on the foraging pastures may determine the timing of the reproductive cycles (Carr and Carr 1970). The feeding grounds of most populations of green turtles are located some distance from their nesting beaches. Tag returns have demonstrated that the feeding grounds for approximately three-quarters of the Tortuguero turtles are the seagrass meadows that blanket the extensive continental shelf of eastern Nicaragua (Carr et al. 1978). Because food is generally unavailable, little or no feeding is believed to take place directly off the nesting beaches, or enroute between breeding and feeding sites. Mortimer (1976, in press) reviewed published accounts of green turtle feeding habits on a worldwide basis. The literature characterizes the turtle as an herbivore that is not averse to eating animals.In most parts of its range the green turtle forages primarily in seagrass pastures (Hirth 1971), e.g., in the western Atlantic north of the equator, in the central Pacific, and in the Indian Ocean (Frazier 1971). In areas where seagrasses are lacking-off the coast of Brazil, Tahiti, Hawaii (Balazs 1979a, b), the Galapagos Islands (Pritchard 1971), and the south African coast (Hughes 1974) -algae are the mainstay of the diet (Hirth 1971). In some localities, however, green turtle colonies that feed mainly on seagrasses occur within a few kilometers of others that forage exclusively on algae. This dichotomy has been reported along the west coast of Honduras (Carr 1952), in the Gulf of California (Felger and Moser 1973), in Fiji (Hirth 1971), in the Gulf of Aden (Hirth et al. 1973), and the Torres Strait of Australia (Nietschmann, in press). The present study is a quantitative analysis of stomach contents from adult green turtles captured on their feeding grounds off the east coast of Nicaragua (fig. 1). In most cases sex and sites of capture were known. The turtles were slaughtered either in Miskito Indian villages for local consumption, or in the two Nicaraguan meat-packing and exporting plants. MATERIALS AND METHODS STOMACH CONTENT ANALYSIS.-The guts of 243 BIOTROPICA 13(1): 49-58 1981 49 This content downloaded from 157.55.39.136 on Thu, 19 May 2016 04:17:56 UTC All use subject to http://about.jstor.org/terms