|Reptilia||< Turtles & tortoises >||Fishes|
Only marine turtles and some South American tortoises exhibit migratory behaviour. Marine turtles are distributed widely in international waters, and adults show a remarkable capacity to return to their tropical and subtropical nesting beaches (Figures A2.76-A2.82). All seven species are listed on CMS Appendices. Some authors consider the black turtle (Chelonia mydas agassizi) as an own species (Figure A2.76). All 7 (or 8) species migrate, and some species cover considerable distances. Goff et al. (1994) have shown that a marked leatherback turtle (Dermochelys coriacea) made 5000 km in only 128 days (Figures A2.81, A2.82). The "least migratory" is the Australian flatback (Natator depressus), which is restricted to coastal waters of Australia and Papua New Guinea. An excellent database of Indopacific nesting beaches is provided online by WCMC42 , and a similar project for the Mediterranean is under way. Extracts from the Indopacific databases have been integrated into the printed maps of Annex II (Figures A2.76-A2.82).
Though many publications stress the poor understanding of sea turtle movements and insufficient monitoring, a review of the available literature reveals an impressive amount of data sets, which should be sufficient for a design of efficient conservation strategies. Besides conservation-oriented articles and handbooks, there are high-quality reports, such as the CMS Technical Publication on Marine Turtles of the Atlantic Coast of Africa (Fretey 1998), long-term data sets for certain nesting areas, or in-depth case studies (see below, and references in captions of Figures A2.76-A2.82). A great number of non-governmental organisations and volunteers are dedicated entirely to the conservation of turtles. Correspondingly, a great number of websites is dedicated to promote turtle conservation, and many contain valuable scientific information. Among the oldest initiatives is the "Archie Carr Center for Sea Turtle Research" (University of Florida), which provides an excellent online-bibliography on all aspects of sea turtle biology.43 The "Mediterranean Association to Save the Sea Turtles" (MEDASSET: http://www.ex.ac.uk/telematics/EuroTurtle/medas/medas.htm) has initiated several monitoring and conservation programmes. Their website contains extensive species accounts, which have been linked to the respective turtle species report within the GROMS database.
Until only few decades ago, sea turtles were slaughtered and exploited for meat on a grand scale. Meanwhile, "sea turtle soup" has disappeared from most western restaurants, thanks to intensive, successful campaigning by conservationists. Though direct exploitation is still a problem in several parts of the world, sea turtles are now facing new threats, such as marine pollution, destruction of coastal habitats and bycatch by modern fisheries, which seem to be even more difficult to combat. Threats have been carefully documented by numerous studies, and some examples are discussed within the respective figure captions (Annex II, Figures A2.76-A2.82) and below. Today, the original state of sea turtle abundance is difficult to imagine, but is vividly described by Long in 1774:
"The greater part of them emigrate from the gulf of Honduras [...] it is affirmed, that vessels, which have lost their latitude in hazy weather, have steered entirely by the noise which this creatures make in swimming, to attain the Cayman isles [...]. In these annual peregrinations across the ocean the resemble [...] herring shoals [...] thus the inhabitants of all these islands are, by the gracious dispensation of the Almighty, benefited in their turn; so that, when the fruit of the earth are deficient, an ample sustenance may still be drawn from this never failing resource of turtle, or their eggs, conducted annually as it were into their very hands [...]." (Long 1774, cited after King 1979; p 184).
The pelagic nature of sea turtles makes them susceptible to fishing gear in international as well as territorial waters. Yatsu et al. (1991) report that the Japanese squid driftnet fishery killed over 500 leatherbacks in two years (1989-1990). The profound study of Chan & Liew (1996) on the decline of the leatherback Dermochelys coriacea in Rantau Abang, Terengganu, Malaysia, provides hard data for fisheries operations being the main factor for the rapid decline of the leatherback in Malaysia. Considerable conservation efforts such as awareness campaigns and establishing of sanctuaries and hatcheries have been made. However, some activities were counterproductive: tourism increased (partly for watching turtles), and sanctuary personnel conducted motorised all-night patrols throughout the sanctuary. Due to these disturbances, turtles appear to have shifted south, but these beaches are developed for industry, tourism and housing. Hatcheries successfully released thousands of turtles, some since the early 1970s. Assuming a 20 year maturation period, recruitment into the breeding population should have started in the 1990s, but populations continued to decline. The authors identified incidental captures in fishing gear (mostly trawl and driftnet) as the main factor of adult mortality. Besides, newly emerged hatchlings are attracted to fishing boats using bright lights at night. The authors conclude that "[...] if mortality of adults and subadults is not reduced, even complete protection of eggs at the nesting beaches would be rendered ineffective", and that only control of fisheries will help to stop adult mortality (Chan & Liew 1996).
Similar frightening declines have been documented from the Eastern Pacific, based on well-documented data from transponder tagging (Spotila et al. 2000). The authors report collapse of nesting populations from Playa Grande, Costa Rica, which was largest nesting colony in the world. From 1,367 leatherbacks nesting in 1988, only 117 were left in 1999. Similar exponential declines have been reported from many other Pacific nesting beaches, including the large Mexican colony (1982: 70,000 to fewer than 250 in 1999). The authors calculated an annual mortality rate between 23% and 33%, which is mainly due to Asian trawl, longline and driftnet, Central and South American longline and gillnet, and Hawaiian longline fisheries. The authors modelled that the species can withstand a maximum of 1% anthropogenic mortality, corresponding to 17 adult and 13 subadult females for the Eastern Pacific, and much lower than the actual bycatch numbers. Spotila et al. (2000) blame Hawaiian longline fishery for the decline of Eastern Pacific leatherbacks (see caption, Figure A2.81). This correlation is questioned by LaGrange (2000), who cites evidence that "mortality associated with the swordfish gillnet fisheries in Peru and Chile represents the single largest source of mortality for East Pacific leatherbacks." In spite of these disputes, it is evident that fishing practices must be changed to save such long-lived species as sea turtles.
All marine turtles are listed in both CMS Appendices, and the "Memorandum of Understanding Concerning Conservation Measures for Marine Turtles of the Atlantic Coast of Africa 1999" has the goal to develop a conservation plan, which "shall aim to improve basic knowledge of species and migration routes, reduce mortality of marine turtles, enhance co-operation among Range States and secure funding for the initiation and/or continuation of conservation programmes." (UNEP-CMS, MoU, 2000). Ongoing monitoring financed by CMS includes the "Sri Lankan Sea by-catch survey and tagging project". Numerous conservation groups are active to save marine turtles, which have become flagship species for the conservation of the marine environment. Besides CMS, there are regional initiatives such as WIDECAST (the Wider Caribbean Sea Turtle Conservation Network),44 TORMED in the Mediterranean, the Marine turtle Conservation Strategy and the Action Plan for the Western Indian Ocean (according to the Sodwana declaration: 1995; National Report of South Africa to CMS, 1997). In addition, the European Community funds projects related to sea turtle conservation within its LIFE framework with considerable budgets (European Community, LIFE database, extracted 7th May 2001). However, most of these projects concentrate on monitoring and protection of nesting beaches, while the detrimental effects of bycatch are neglected.
An impressive number of sea turtle conservation networks run projects including captive rearing and releasing of hatchlings ("headstarting"). But Heppell & Crowder (1998) argue that conservation measures should focus on re-establishing adult stocks and protecting subadults. This may restore
declining populations more effectively. Especially in late-maturing species, an increase in juvenile cohort size does not necessarily increase population growth significantly. The authors show that the main mortality factor for Lepidochelys kempii is incidental drowning of large juveniles and adults in shrimp trawls, thereby destroying the results of captive-rearing and release efforts. Eckert & Honebrink et al. (1992) attribute inefficiency of fishery legislation for St. Kitts and Nevis45 to protection of small turtles alone, while large juveniles and adults could be taken eight months of the year. Such bad practice affects all sea turtles of the Wider Caribbean, due to their highly migratory behaviour. A decade later, the recommendations of the authors are still not enforced.
|42||Marine turtle nesting database: http://www.unep-wcmc.org.uk/marine/mturtle/home.htm|
|44||Carribean Environment Program CEP: http://www.cep.unep.org/|
|45||As part of the Caribbean Environment Program CEP: http://www.cep.unep.org/|
|Reptilia||< Turtles & tortoises >||Fishes|
This document should be quoted as part of the publication "Riede, K. (2001): The Global Register of Migratory Species Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD
by Klaus Riede