|Scientific Name:||Chelonia mydas (Linnaeus, 1758)|
|Infra-specific Taxa Assessed:|
Testudo mydas Linnaeus, 1758
|Red List Category & Criteria:||Endangered A2bd ver 3.1|
|Assessor(s):||Seminoff, J.A. (Southwest Fisheries Science Center, U.S.)|
|Reviewer(s):||Crouse, D. & Pilcher, N. (Marine Turtle Red List Authority)|
Analysis of historic and recent published accounts indicate extensive subpopulation declines in all major ocean basins over the last three generations as a result of overexploitation of eggs and adult females at nesting beaches, juveniles and adults in foraging areas, and, to a lesser extent, incidental mortality relating to marine fisheries and degradation of marine and nesting habitats. Analyses of subpopulation changes at 32 Index Sites distributed globally (Figure 1, Table 1; see the supplementary material) show a 48% to 67% decline in the number of mature females nesting annually over the last 3–generations.
Assessment Procedure: In accord with the IUCN criterion that Red List Assessments focus on the number of mature individuals (IUCN 2001a), this assessment measures changes in the annual number of nesting females. Because reliable data are not available for all subpopulations, the present report focuses on 32 Index Sites (Figure 1, Table 1; see the supplementary material). These Index Sites include all of the known major nesting areas as well as many of the lesser nesting areas for which quantitative data are available. Despite considerable overlap at some foraging areas, each is presumed to be genetically distinct (Bowen et al. 1992, Bowen 1995) except for the Turtle Islands of Malaysia (Sabah) and Philippines (Moritz et al. 1991). These two Index Sites are, however, treated independently because of the different management practices exercised by the two governments and the resultant differences in subpopulation trends. Selection of the 32 Index Sites was based on two primary assumptions: (1) they represent the overall regional subpopulation trends and (2) the number of individuals among Index Sites in each region is proportional to the actual population size in that region. Any regional inconsistencies in this proportion may result in a biased global population estimate.
It should be noted that a major caveat of using the number of nesting females to assess population trends is that this data type provides information for the proportion of the adult females that nest in any given year, not the total adult female population. However, when monitored over many years, this index can be reliable for assessing long-term population trends (Meylan 1982, Limpus 1996). In the case of green turtles, which display high inter-annual variability in magnitude of nesting (Limpus and Nichols 1987, Broderick et al. 2001a), using short-term or single-season data sets could misrepresent the actual mean number of nesters over a longer timeframe. To alleviate this potential source of error, we used multiple-year data sets whenever available. However, when single-season datasets represented the only quantitative information for a given time period, these data were used as long as they were in accord with qualitative information from other references.
Because data on annual number of nesting females are not always available, we also used data on number of nests per season, annual hatchling production, annual egg production and annual egg harvest. When these proxies were used, we converted units to number of nesting females based on a constant figure of 100 eggs/nest and three nests/season/female, unless otherwise noted. These conversions were based on the assumptions that (1) the mean number of eggs/nest and nests/female/season differ insignificantly through time, and (2) efforts to monitor nesting female activity and egg production are consistent through time. When using egg harvest data, we also assumed that harvest effort was consistent during all years for which data are available and 100% of the eggs were harvested in any given year. We believe these assumptions are accurate, but their absolute validation is very difficult. Qualitative information does, however, suggest that they are reasonable assumptions. For example, in the case of historic egg harvest, the same group of people usually harvested the eggs at a particular nesting beach each year, and they typically took every egg they could find (e.g., Parsons 1962, Pelzer 1972).
In the present assessment, population abundance estimates are based on raw data, linear extrapolation functions, and exponential extrapolation functions. In most subpopulations, more than one trajectory was exhibited over the 3–generation interval; changes in subpopulation size are thus often based on a combination of raw data and extrapolations. If no change is believed to have occurred outside the time interval for which published abundance data are available, the raw data were used to determine the change in population size. However, when it is believed that change in subpopulation abundance occurred outside the interval for which raw data were available, extrapolations we performed to determine the overall change. Linear extrapolations were used when it was believed that the same amount of change occurred each year, irrespective of total subpopulation size. Exponential extrapolations were used when it was believed that change was proportional to the subpopulation size. In cases where there is a lack of information on the specific rate of change, both linear and exponential extrapolations were used to derive population estimates. However, if extrapolations resulted in obviously false estimates, their results were discarded (see Table 5; see the supplementary material).
Generation Length. Generation length is based on the age to maturity plus one half the reproductive longevity (Pianka 1974). Although there appears to be considerable variation in generation length among sea turtle species, it is apparent that all are relatively slow maturing and long-lived (Chaloupka and Musick 1997). Green turtles exhibit particularly slow growth rates, and age to maturity for the species appears to be the longest of any sea turtle (Hirth 1997). As a result, this assessment uses the most appropriate age-at-maturity estimates for each index site. At Index Sites for which there are local age-to-maturity data, those data are used to establish generation length. When data are lacking, as they are for a majority of subpopulations, information from the closest subpopulation for which data are available are used to generate age-at-maturity estimates (Table 2; see the supplementary material).
Estimates of reproductive longevity range from 17 y to 23 y (Carr et al. 1978, Fitzsimmons et al. 1995). Data from the apparently pristine Green Turtle stock at Heron Island in Australia’s southern Great Barrier Reef show a mean reproductive life of 19 y (Chaloupka et al. 2004). Because Heron Island is the only undisturbed stock for which reproductive longevity data are available (M. Chaloupka, pers. comm.), this datum is used for all Index Sites (Table 3; see the supplementary material). Thus, based on the range of ages-at-sexual-maturity (26 yrs to 40 yrs) and reproductive longevity from the undisturbed Australian stock (19 yr), the generation lengths used for this assessment range from 35.5 yrs to 49.5 yrs (Table 3; see the supplementary material).
Uncertainties in assessment process: As with any assessment based on historic data or small datasets, there is a great deal of uncertainty relating to the final results of this report. The sources of uncertainty are rooted in both the procedure itself as well as in the stochastic nature green of turtle biology. Both sources of uncertainty are ultimately related to a lack of information, which can be a common issue when dealing with an animal as long-lived as a Green Turtle.
First and foremost is the uncertainty related to the assumptions invoked for this assessment. For example, if, contrary to our assumption, efforts to monitor nesting female activity and egg production were not consistent through time, then our results may be biased. Similarly, our estimates may be inaccurate if harvest effort or the relative amount of eggs harvested was not consistent through time. In addition, the use of extrapolations may have resulted in erroneous estimates of population change. The potential for this increased when extrapolations were made over long time intervals, when they were based on short-term data sets, or if the start and/or end points of extrapolations were erroneous.
Uncertainty may also be tied to Green Turtle biology. In particular, the substantial variability in the proportion of a population that nests in any given year may result in inaccurate comparisons between past and present data sets. For example, if the proportion of a subpopulation’s adult female cohort nesting each year oscillates over decadal or longer time frames, then it is conceivable that our estimates of annual change in nesting numbers do not correspond to actual changes in the entire subpopulation. Moreover, if our conversion values for eggs/nest and nests/female/season are not accurate for the specific subpopulation being addressed, inaccuracies may result. Lastly, with respect to the migratory behaviour of green turtles, it is expected that each of the Index Sites included in this assessment represent a distinct subpopulation. Indeed, current genetic data support this claim, however, in the absence of complete data for all rookeries, it is possible that turtles moving back and forth between nesting areas in close proximity could have gone undetected. It is thus conceivable that a female could be counted twice. This would, of course, only be a problem when subpopulation size is based on an actual count of individual turtles visiting the beach. Although unlikely, it amounts to an additional source of uncertainty in this assessment.
Population trends. Based on the actual and extrapolated changes in subpopulation size at the 32 Index Sites, it is apparent that the mean annual number of nesting females has declined by 48% to 67% over the last three generations (Table 5; see the supplementary material). In addition, it is apparent that the degree of population change is not consistent among all Index Sites or among all regions (Tables 5 and 6; see the supplementary material). Because many of the threats that have led to these declines are not reversible and have not yet ceased, it is evident that green turtles face a measurable risk of extinction. Based on this assessment, it is apparent that green turtles qualify for Endangered status under Criteria A2bd.
The key supporting documentation is presented in the tables (see link to additional information below), and the full assessment is also available from the Marine Turtle Specialist Group web site.
|Previously published Red List assessments:|
|Range Description:||The Green Turtle has a circumglobal distribution, occurring throughout tropical and, to a lesser extent, subtropical waters (Atlantic Ocean – eastern central, northeast, northwest, southeast, southwest, western central; Indian Ocean – eastern, western; Mediterranean Sea; Pacific Ocean – eastern central, northwest, southwest, western central). Green turtles are highly migratory and they undertake complex movements and migrations through geographically disparate habitats. Nesting occurs in more than 80 countries worldwide (Hirth 1997). Their movements within the marine environment are less understood but it is believed that green turtles inhabit coastal waters of over 140 countries (Groombridge and Luxmoore 1989).|
Native:American Samoa; Angola; Anguilla; Antigua and Barbuda; Australia (Ashmore-Cartier Is., Coral Sea Is. Territory, Northern Territory, Queensland, Western Australia); Bahrain; Bangladesh; Barbados; Belize; Bonaire, Sint Eustatius and Saba (Saba, Sint Eustatius); Brazil; British Indian Ocean Territory; China; Christmas Island; Cocos (Keeling) Islands; Colombia; Comoros; Cook Islands; Costa Rica; Cuba; Curaçao; Cyprus; Dominica; Dominican Republic; Ecuador (Galápagos); Egypt; Equatorial Guinea (Bioko); Eritrea; Fiji; French Guiana; French Polynesia; French Southern Territories (Mozambique Channel Is.); Grenada; Guam; Guinea; Guinea-Bissau; Guyana; Haiti; India (Andaman Is., Gujarat, Laccadive Is., Nicobar Is.); Indonesia (Bali, Jawa, Kalimantan, Lesser Sunda Is., Maluku, Papua, Sulawesi, Sumatera); Iran, Islamic Republic of; Jamaica; Japan (Honshu, Nansei-shoto, Ogasawara-shoto); Kenya; Kiribati; Kuwait; Madagascar; Malaysia (Peninsular Malaysia, Sabah, Sarawak); Maldives; Marshall Islands; Martinique; Mauritania; Mayotte; Mexico (Baja California, Campeche, Michoacán, Quintana Roo, Revillagigedo Is., Sinaloa, Sonora, Tabasco, Tamaulipas, Veracruz, Yucatán); Micronesia, Federated States of ; Mozambique; Myanmar; New Caledonia; New Zealand (Kermadec Is., North Is., South Is.); Nicaragua; Niue; Northern Mariana Islands; Oman; Pakistan; Palau; Panama; Papua New Guinea; Peru; Philippines; Puerto Rico; Saint Helena, Ascension and Tristan da Cunha (Ascension); Saint Kitts and Nevis; Saint Lucia; Saint Martin (French part); Saint Vincent and the Grenadines; Sao Tomé and Principe; Saudi Arabia; Senegal; Seychelles; Sierra Leone; Sint Maarten (Dutch part); Solomon Islands; Somalia; Sri Lanka; Suriname; Tanzania, United Republic of; Thailand; Timor-Leste; Tokelau; Tonga; Trinidad and Tobago; Turkey; Turks and Caicos Islands; Tuvalu; United Arab Emirates; United States (Florida, Hawaiian Is.); United States Minor Outlying Islands (Midway Is., US Line Is.); Vanuatu; Venezuela, Bolivarian Republic of (Aves I., Venezuelan Antilles); Viet Nam; Virgin Islands, British; Virgin Islands, U.S.; Yemen
Regionally extinct:Cayman Islands; Mauritius (Rodrigues - Native)
|FAO Marine Fishing Areas:|
Atlantic – southwest; Atlantic – northwest; Atlantic – northeast; Atlantic – western central; Atlantic – eastern central; Atlantic – southeast; Indian Ocean – western; Indian Ocean – eastern; Mediterranean and Black Sea; Pacific – southwest; Pacific – eastern central; Pacific – western central; Pacific – northwest
|Range Map:||Click here to open the map viewer and explore range.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Like most sea turtles, green turtles are highly migratory and use a wide range of broadly separated localities and habitats during their lifetimes (for review see Hirth 1997). Upon leaving the nesting beach, it has been hypothesized that hatchlings begin an oceanic phase (Carr 1987), perhaps floating passively in major current systems (gyres) that serve as open-ocean developmental grounds (Carr and Meylan 1980, Witham 1991). After a number of years in the oceanic zone, these turtles recruit to neritic developmental areas rich in seagrass and/or marine algae where they forage and grow until maturity (Musick and Limpus 1997). Upon attaining sexual maturity green turtles commence breeding migrations between foraging grounds and nesting areas that are undertaken every few years (Hirth 1997). Migrations are carried out by both males and females and may traverse oceanic zones, often spanning thousands of kilometers (Carr 1986, Mortimer and Portier 1989). During non-breeding periods adults reside at coastal neritic feeding areas that sometimes coincide with juvenile developmental habitats (e.g., Limpus et al. 1994, Seminoff et al. 2003).|
|Movement patterns:||Full Migrant|
|Major Threat(s):||Green turtles, like other sea turtle species, are particularly susceptible to population declines because of their vulnerability to anthropogenic impacts during all life-stages: from eggs to adults. Perhaps the most detrimental human threats to green turtles are the intentional harvests of eggs and adults from nesting beaches and juveniles and adults from foraging grounds. Unfortunately, harvest remains legal in several countries despite substantial subpopulation declines (e.g., Humphrey and Salm 1996, Fleming 2001, Fretey 2001). In addition, a number of incidental threats impact green turtles around the world. These threats affect both terrestrial and marine environments, and include bycatch in marine fisheries, habitat degradation at nesting beaches and feeding areas, and disease. Mortality associated with entanglement in marine fisheries is the primary incidental threat; the responsible fishing techniques include drift netting, shrimp trawling, dynamite fishing, and long-lining. Degradation of both nesting beach habitat and marine habitats also play a role in the decline of many Green Turtle stocks. Nesting habitat degradation results from the construction of buildings, beach armoring and re-nourishment, and/or sand extraction (Lutcavage et al. 1997). These factors may directly, through loss of beach habitat, or indirectly, through changing thermal profiles and increasing erosion, serve to decrease the quantity and quality of nesting area available to females, and may evoke a change in the natural behaviors of adults and hatchlings (Ackerman 1997). The presence of lights on or adjacent to nesting beaches alters the behavior of nesting adults (Witherington 1992) and is often fatal to emerging hatchlings as they are attracted to light sources and drawn away from the water (Witherington and Bjorndal 1990). Habitat degradation in the marine environment results from increased effluent and contamination from coastal development, construction of marinas, increased boat traffic, and harvest of nearshore marine algae resources. Combined, these impacts diminish the health of coastal marine ecosystems and may, in turn, adversely affect green turtles. For example, degradation of marine habitats has been implicated in the increasing prevalence of the tumor-causing Fibropapilloma disease (George 1997).|
Green turtles have been afforded legislative protection under a number of treaties and laws (e.g., Navid 1982, Humphrey and Salm 1996, Fleming 2001, Fretey 2001). Among the more globally relevant designations are those of Endangered by the World Conservation Union (IUCN; Baillie and Groombridge 1996, Hilton-Taylor 2000); Annex II of the SPAW Protocol to the Cartagena Convention (a protocol concerning specially protected areas and wildlife); Appendix I of CITES (Convention on International Trade in Endangered Speciesof Wild Fauna and Flora); and Appendices I and II of the Convention on Migratory Species (CMS). A partial list of the International Instruments that benefit green turtles includes the Inter-American Convention for the Protection and Conservation of Sea Turtles, the Memorandum of Understanding on the Conservation and Management of Marine Turtles and their Habitats of the Indian Ocean and South-East Asia (IOSEA), the Memorandum of Understanding on ASEAN Sea Turtle Conservation and Protection, the Memorandum of Agreement on the Turtle Islands Heritage Protected Area (TIHPA), and the Memorandum of Understanding Concerning Conservation Measures for Marine Turtles of the Atlantic Coast of Africa.
As a result of these designations and agreements, many of the intentional impacts directed at sea turtles have been lessened: harvest of eggs and adults has been slowed at several nesting areas through nesting beach conservation efforts and an increasing number of community-based initiatives are in place to slow the take of turtles in foraging areas. In regard to incidental take, the implementation of Turtle Excluder Devices has proved to be beneficial in some areas, primarily in the United States and South and Central America (National Research Council 1990). However, despite these advances, human impacts continue throughout the world. The lack of effective monitoring in pelagic and near-shore fisheries operations still allows substantial direct and indirect mortality, and the uncontrolled development of coastal and marine habitats threatens to destroy the supporting ecosystems of long-lived green turtles.
|Citation:||Seminoff, J.A. (Southwest Fisheries Science Center, U.S.). 2004. Chelonia mydas. The IUCN Red List of Threatened Species 2004: e.T4615A11037468.Downloaded on 20 April 2018.|
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