Marine Turtles of the Western Indian Ocean

Abstract

After seven years' study, visiting islands scattered over more than a million square miles of the western Indian Ocean, where once hundreds of thousands of green turtles nested every year, the author's "optimistic estimate" of the number of females nesting today is 5500. Only eighty years ago 12,000 were taken in one year on Aldabra alone. Over-exploitation by man for food -both of nesting females and eggs -and destruction of nesting habitat, i.e. disturbance of the beaches, are the two factors that are destroying this immensely valuable resource. The author's study was assisted by FPS.For seven years, 1968-74, 1 have been studying sea turtles in the western Indian Ocean, and only now do I feel able to report on their status in the area north of Madagascar: Seychelles, British Indian Ocean Territory (BIOT), Gloriosa, Comoros, and offshore islands north-east of Madagascar. Many of the islands studied were once famous for their vast numbers of turtles, which had thrived for untold centuries. But in the last hundred years exploitation by man has reduced the populations, as well as other natural resources, catastrophically, and a survey of the population trends and the status of both the turtles and their nesting and feeding grounds had become urgent. However, getting to small, remote islands is not easy at the best of times, and even when you do it is not always possible to land. The study area covers over a million square miles. In Seychelles alone there are nearly a hundred islands, and even after seven years of study, sailing over tens of thousands of miles of ocean, and walking hundreds of miles of beaches, there are beaches I have still not surveyed and some islands I have never seen. However, I have visited all the most important beaches, and there is no indication that the few unsurveyed ones would invalidate my conclusions.Only two species of marine turtle are common in the western Indian Ocean: the green Chelonia mydas, famous for its contribution to turtle soup, and the smaller hawksbill Erermochelys imbricata, known for its beautiful shell that is made into jewellery and curios. Loggerhead, ridley, and leathery turtles are found only rarely in these waters. Estimating the population of an animal that ranges over thousands of miles of ocean, and still guards many important secrets of its life history (e.g. time taken to mature), is something of a "guestimate". However, nesting females coming ashore leave conspicuous tracks and nest pits on the beach, and these can be counted with some Above HAWKSBILL nesting under a casuarina tree

Marine and Coastal Protected Areas: A Guide for Planners and Managers

“…The workers greatly relished green turtle meat and eggs and historical documents indicate that exploitation of hawksbill shell occurred throughout the period of human settlement. Export statistics are available only for the present century, but show a decline in the numbers of hawksbills captured between 1904 and 1929 (Frazier, 1977). Historical documents also indicate that the abundance of both green turtles and hawksbills was much greater during the early years of settlement (Mortimer & Day, 1999).…”

“…Although regulations were enacted in 1968 to prohibit the take of green turtles, interviews with island residents in 1970 indicated a continuing harvest (Frazier, 1977). The harvest was effectively terminated during 1970 and 1971, however, when the last island residents were evacuated to Mauritius in preparation for an Anglo-American military base which was constructed and has been active ever since (Stoddart, 1971).…”

“…In 1970, Frazier (1977 estimated the nesting population to number some 300 females of each species. Data collected by Mortimer (Mortimer & Day, 1999) during a six week survey of the archipelago in 1996 indicate that twice as many turtles now nest annually, including some 400-800 green turtles and 300-700 hawksbills.…”

Seasonality, abundance, and fifteen-year trend in green turtle nesting activity at Itsamia, Moheli, Comoros

“…It is listed on the IUCN Red List (www.iucnredlist.org), primarily because of the overexploitation of eggs and adults on nesting beaches as well as bycatch in fisheries and perturbation to both nesting and feeding habitats (Seminoff 2004). Indeed, there is considerable evidence of significant population declines of green turtles over the past few centuries, especially in the Indian Ocean region, most of which is thought to be due to overexploitation and destruction of nesting and foraging habitats (Frazier 1975. Nonetheless, the SWIO has hosted some of the world's most important nesting and feeding grounds for green turtles (Frazier 1971, 1975, 1984, Hughes 1973, Le Gall et al 1986, Le Gall 1988.…”

“…Indeed, there is considerable evidence of significant population declines of green turtles over the past few centuries, especially in the Indian Ocean region, most of which is thought to be due to overexploitation and destruction of nesting and foraging habitats (Frazier 1975. Nonetheless, the SWIO has hosted some of the world's most important nesting and feeding grounds for green turtles (Frazier 1971, 1975, 1984, Hughes 1973, Le Gall et al 1986, Le Gall 1988. This region, defined here as the waters bounded by the eastern coast of Africa extending from Kenya to South Africa and east as far as 60º E, nowadays includes major green turtle nesting areas such as Europa and Tromelin Islands (Lauret-Stepler et al 2007), Aldabra Atoll (Frazier 1971, 1984, Mortimer 1985, Mortimer et al 2011a, and Mayotte (Bourjea et al 2007a), where each island/atoll regularly hosts thousands of annual nesters.…”