World Status, Exploitation and Trade - WIDECAST

INTRODUCTIONSUMMARY1. Recent investigations into the systematics of sea turtles are few; thepresent sub-generic taxonomy is unsatisfactory, and unlikely adequately toreflect between-populat ion genetic variation.2. It is difficult to estimate population size and trends in sea turtles.Although some feeding ground aggregations have been studied, it is onlypossible to assess population size by means of an estimate of the number ofmature females that emerge on a given nesting beach. Because femalestypically nest on two- to three-year cycles, the annual nesting contingentwill be a minor proportion of the total adult female population. Becausemassive fluctuation in annual nesting numbers has been demonstrated atseveral sites, population trends can only reliably be distinguished as aresult of long-term field studies. Hawksbill numbers are particularlydifficult to assess because females tend to nest singly or in small numbers,often on small unsurveyed beaches.3. Virtually all reported between-season recoveries of nesting femalestagged on their nest beach have occurred on the same beach (most data relateto C. mydas , the subject of most tagging operations). This precise hominghas led to the prevailing view that nesting beach populations are isolatedgenetically from one another. There is evidence for very occasionaldispersal of females to different nest sites, and for sufficient flexibilityto allow slow colonisation of new nesting sites. Significant gene flow mustoccur if turtles do not nest on their own natal beach. However, noextirpated nesting population has been seen to be replenished by otherpopulations, and the precise homing that has been shown to occur amongmature animals nesting in their second or subsequent season means that eachnest site population must be treated separately for conservation andmanagement purposes.4. Growth rates are likely to be partly dependent on food supply, but theavailable data show that maturation in C. mydas is attained after a longperiod of between 20 and 50 years; present indications are that E. imbricatamay be similar, although a higher growth rate has been demonstrated at onesite holding both species. The practical importance of late maturation isthat the effects of human interference with wild populations, whetheradverse or beneficial, can be masked for many years. Over-exploitation maynot be evident because it would theoretically be possible to take every eggor adult from a nest beach for some 20 years with little obvious effect, asnewly maturing females would still emerge to nest during this period; butthe population would then crash because recruitment had ceased some 20 yearsin the past.5. Eggs of all sea turtle species are widely collected for directsubsistence or medicinal use, or for sale, usually locally or nationally.Turtle oil is used for fuel, as a lubricant and waterproofing agent, and formedicinal and cosmetic purposes. Green Turtle meat and cartilage are widelyconsumed for subsistence purposes, and, as ingredients of 'turtle soup', asa luxury foodstuff in international trade. Between 40% and 50% of the wetweight of a Green Turtle comprises edible protein; a sub-adult or adultindividual might weigh in the region of 100 kg. Hawksbill meat is consumedless regularly, and is sometimes highly poisonous. Hawksbills are usedmainly for their shell, known as "tortoiseshell"; the shell of Green Turtlesis too thin for carving and is rarely traded. A market has been created inthe last few decades for turtle skin; Olive Ridley Lepidochelys olivacea is