World Status, Exploitation and Trade - WIDECAST

INTRODUCTIONextremely heavy harvesting regimes are surprisingly slow. Pritchard (1982c)pointed out that "rapid recovery of a Green Turtle population that has beensubject to complete or nearly complete egg exploitation is probablyimpossible", saying that such populations might need protection for severaldecades before they would show signs of recovery. Thus, although eggharvesting has the potential for being a good way of sustainably harvestingsea turtle populations, it has its dangers, and requires far greater controlthan is usually exercised. Some of the financial implications ofsustainable egg harvesting are discussed later.Turtle harvestsThis category will be taken to include any killing of post-hatchi ingturtles, from juveniles up to mature breeding adults. For practicalreasons, it is usually breeding animals that are taken. Several authors(e.g. King, 1982; Mrosovsky, 1983) have commented on the dismal history ofexploitation of adult C. mydas which has frequently resulted in the localdepletion of populations, in some cases leading to extinction. Techniquesfor estimating turtle populations have only recently been developed, and soit is rarely possible to document trends in wild populations; more often thehistorical harvest figures are used to indicate what the wild populationsonce were. However, some indication of the past impact of turtleexploitation can be inferred from the present distribution of turtles.Nearly all of the major remaining Green Turtle rookeries are located onislands. This is not for want of any suitable sandy beaches on themainland, and so some other explanation mus*: be sought. The most plausiblehypothesis is because of disturbance or predation by terrestrial animals. Avariety of non-human predators are known to dig up and destroy turtle nests,and in some cases this may result in heavy mortality. The predators rangefrom ants to pigs and many are absent from offshore islands (Stancyk,1982). Some of the worst predators, feral pigs and dogs, are associatedwith human presence, but their effect is probably minimal in comparison withdirect human predation. Only humans regularly kill substantial numbers ofadult turtles; the other predators mostly confine themselves to eggs, andthis form of exploitation is thought to be less damaging. It thus appearsthat human predation may be primarily responsible for the presentdistribution of turtle nesting colonies, and this is corroborated by thefact that several islands which formerly held breeding colonies are known tohave lost them only after they became inhabited by humans. Examples includeMauritius, Reunion, the Cayman Islands and Bermuda. Mainland nestingcolonies in the New World, particularly Mexico, but also Colombia andothers, have been depleted in historical times after the onset of humanexploitation, and the only remaining mainland nesting beaches are in placeswhere they have not, until recently, been much exploited. This may be forreasons of inaccessibility, such as Costa Rica, or because of religiouscustoms forbidding the consumption of turtle meat, such as Somalia, theArabian Peninsula, Burma, Malaysia and, formerly, Indonesia. Africa, thecontinent with the longest history of human habitation, has no largemainland rookeries of C. mydas outside Somalia. Of course, it could beargued that it was not necessarily predation killing turtles, butdisturbance that had caured turtles to move to offshore islands. However,the marked philopatry of nesting turtles argues against this.There is also some good documented evidence of declines in C. mydaspopulations subject to heavy exploitation (see Table 11). Some of thesedeclines have been extremely rapid. The vast Cayman Island rookery was27