Dermochelys coriacea (Southwest Atlantic Ocean subpopulation)
|Scientific Name:||Dermochelys coriacea (Southwest Atlantic Ocean subpopulation)|
|Red List Category & Criteria:||Critically Endangered D ver 3.1|
|Assessor(s):||Tiwari, M., Wallace, B.P. & Girondot, M.|
|Reviewer(s):||Casale, P., Dutton, P.H., Eckert, K.L., Miller, J., Mortimer, J.A., Nel, R., Pritchard, P.C.H., van Dijk, P.P., Bolten, A.B., Musick, J.A., Limpus, C. & Dobbs, K.|
|Contributor(s):||Marcovaldi, M., Fallabrino, A., Lopez-Mendilaharsu, M., de Padua Almeida, A. & Thome, J.|
The Southwest Atlantic Leatherback subpopulation nests only in southern Brazil (Thomé et al. 2007), and this rookery is genetically distinct from all other sampled rookeries in the Atlantic (Dutton et al. 2013). The marine habitat for this subpopulation is thought to extend north across the equator and east to the coast of Atlantic Africa, southwest to Uruguay and Argentina, and southeast to South African waters (see Figure 1 in Supplementary Material). However, the geographic boundaries for this subpopulation lack resolution.
Application of Criterion A2 is appropriate, as population reduction may have been observed in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible. This subpopulation is increasing by 232%, and will increase by 957% in another generation (i.e., by 2040), with an abundance of approximately 169 nests (~34 females) per year, or approximately 85 adult females total.
We assessed the status of the Southwest Atlantic Leatherback subpopulation by Criteria A-D; as no population viability analysis has been performed, Criterion E could not be applied.
Leatherback age at maturity is uncertain, and estimates range widely (see Jones et al. 2011 for review). Reported estimates fall between 9-15 yr, based on skeletochronology (Zug and Parham 1996), and inferences from mark-recapture studies (Dutton et al. 2005). Furthermore, updated skeletochronological analyses estimated Leatherback age at maturity to be between 26-32 yr (mean 29 yr) (Avens et al. 2009). Extrapolations of captive growth curves under controlled thermal and trophic conditions suggested that size at maturity could be reached in 7-16 yr (Jones et al. 2011). Thus, a high degree of variance and uncertainty remains about Leatherback age at maturity in the wild. Likewise, Leatherback lifespan is unknown. Long-term monitoring studies of Leatherback nesting populations have tracked individual adult females over multiple decades (e.g. Santidrián Tomillo et al. unpublished data, Nel and Hughes unpublished data), but precise estimates of reproductive lifespan and longevity for Leatherbacks are currently unavailable.
Although monitoring of nesting activities by adult female sea turtles is the most common metric recorded and reported across sites and species, globally, there are several disadvantages to using it as a proxy for overall population dynamics, some methodological, some interpretive (NRC 2010). First, because nesting females are a very small proportion of a sea turtle population, using abundance of nesting females and their activities as proxies for overall population abundance and trends requires knowledge of other key demographic parameters (several mentioned below) to allow proper interpretation of cryptic trends in nesting abundance (NRC 2010). However, there remains great uncertainty about most of these fundamental demographic parameters for Leatherbacks, including age at maturity (see Jones et al. 2011 for review), generation length, survivorship across life stages, adult and hatchling sex ratios, and conversion factors among reproductive parameters (e.g., clutch frequency, nesting success, re-migration intervals, etc.). These values can vary among subpopulations, further complicating the process of combining subpopulation abundance and trend estimates to obtain global population abundance and trend estimates, and contributing to the uncertainty in these estimates. For example, in the present case of the Southwest Atlantic Leatherback subpopulation, our assumption of 3:1 female:male sex ratio has a significant impact on the estimate of mature individuals in the subpopulation; i.e. under the assumption of a 1:1 sex ratio, the number of mature individuals (n=54) would have exceeded the threshold for Critically Endangered, thus qualifying this subpopulation for the Endangered category. Our assumption was based on published data (Barata et al. 2004), but more information is needed to increase confidence in this assumption of adult sex ratios, as well as assumptions included in estimates of other demographic parameters.
Leatherbacks are distributed circumglobally, with nesting sites on subtropical and tropical sandy beaches and foraging ranges that extend into temperate and sub-polar latitudes. See Eckert et al. (2012) for review of Leatherback geographic range. The Southwest Atlantic Leatherback subpopulation nests only in Brazil (Thomé et al. 2007) and its marine habitat is thought to extend north across the equator in Brazil and east to the coast of Atlantic Africa, southwest to southern Brazil, Uruguay, and Argentina, and southeast to South African waters (see Figure 1 in Supplementary Material); however, the geographic boundaries for this subpopulation lack resolution.
Native:Angola; Argentina; Benin; Brazil; Cameroon; Congo; Congo, The Democratic Republic of the; Côte d'Ivoire; Equatorial Guinea; Gabon; Gambia; Guinea; Guinea-Bissau; Liberia; Namibia; Nigeria; Saint Helena, Ascension and Tristan da Cunha; Sao Tomé and Principe; Senegal; Sierra Leone; South Africa; Togo; Uruguay
|FAO Marine Fishing Areas:|
Atlantic – western central; Atlantic – southwest; Atlantic – southeast; Atlantic – northwest; Atlantic – northeast; Atlantic – eastern central
|Range Map:||Click here to open the map viewer and explore range.|
Leatherbacks are a single species globally comprised of biologically described regional management units (RMUs; Wallace et al. 2010), which describe biologically and geographically explicit population segments by integrating information from nesting sites, mitochondrial and nuclear DNA studies, movements and habitat use by all life stages. RMUs are functionally equivalent to IUCN subpopulations, thus providing the appropriate demographic unit for Red List assessments. There are seven Leatherback subpopulations, including the Southwest Atlantic Ocean, Southeast Atlantic Ocean, Northwest Atlantic Ocean, Northeast Indian Ocean, Southwest Indian Ocean, East Pacific Ocean, and West Pacific Ocean. Multiple genetic stocks have been defined according to geographically disparate nesting areas around the world, and in the Atlantic Ocean in particular (Dutton et al. 1999, 2013), and are included within RMU delineations (Wallace et al. 2010; shapefiles can be viewed and downloaded at: http://seamap.env.duke.edu/swot).
|Current Population Trend:||Increasing|
|Habitat and Ecology:|
See the species account for a summary of the details. For a thorough review of Leatherback biology, please see Eckert et al. (2012).
|Generation Length (years):||30|
|Movement patterns:||Full Migrant|
|Congregatory:||Congregatory (and dispersive)|
|Use and Trade:||Harvest of eggs has been minimized and human exploitation of females is non-existent.|
Threats to Leatherbacks (and other marine turtle species), vary in time and space, and in relative impact to populations. Threat categories were defined by Wallace et al. (2011) as the following:
1) Fisheries bycatch: incidental capture of marine turtles in fishing gear targeting other species;
2) Take: direct utilization of turtles or eggs for human use (i.e. consumption, commercial products);
3) Coastal Development: human-induced alteration of coastal environments due to construction, dredging, beach modification, etc.;
4) Pollution and Pathogens: marine pollution and debris that affect marine turtles (i.e. through ingestion or entanglement, disorientation caused by artificial lights), as well as impacts of pervasive pathogens (e.g. fibropapilloma virus) on turtle health;
5) Climate change: current and future impacts from climate change on marine turtles and their habitats (e.g. increasing sand temperatures on nesting beaches affecting hatchling sex ratios, sea level rise, storm frequency and intensity affecting nesting habitats, etc.).
The relative impacts of individual threats to all Leatherback subpopulations were assessed by Wallace et al. (2011). At a global scale, fisheries bycatch was classified as the highest threat to Leatherbacks globally, followed by human consumption of Leatherback eggs, meat, or other products and coastal development. Due to lack of information, pollution and pathogens was only scored in three subpopulations and climate change was only scored in two subpopulations. Enhanced efforts to assess the impacts of these threats on Leatherbacks—and other marine turtle species—should be a high priority for future research monitoring efforts.For the Southwest Atlantic subpopulation, harvest of eggs has been minimized and human exploitation of females is non-existent, however, accidental capture in fisheries is one of the biggest threats (Pinedo and Polachek 2004, Domingo et al. 2006, Gallo et al. 2006, Lopez Mendilaharsu et al. 2007, Thomé et al. 2007, Bugoni et al. 2008, Fiedler et al. 2012, Wallace et al. 2013).
Leatherbacks are protected under various national and international laws, treaties, agreements, and memoranda of understanding. A partial list of international conservation instruments that provide legislative protection for leatherbacks are: 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 Species of Wild Fauna and Flora); and Appendices I and II of the Convention on Migratory Species (CMS); the Inter-American Convention for the Protection and Conservation of Sea Turtles (IAC), 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, and the Memorandum of Understanding Concerning Conservation Measures for Marine Turtles of the Atlantic Coast of Africa.Long-term efforts to reduce or eliminate threats to Leatherbacks on nesting beaches have been successful (e.g. Dutton et al. 2005, Chacón-Chaverri and Eckert 2007, Sarti Martínez et al. 2007). Reducing Leatherback bycatch has become a primary focus for many conservation projects around the world, and some mitigation efforts are showing promise (Watson et al. 2005; Gilman et al. 2006, 2011). However, threats to Leatherbacks—bycatch and egg consumption and female exploitation, in particular, persist, and in some places, continue to hinder population recovery (Bellagio report 2007, Bal et al. 2007, Fretey et al. 2007, Alfaro-Shigueto et al. 2011, Riskas and Tiwari 2013, Wallace et al. 2013). For depleted Leatherback populations to recover, the most prevalent and impactful threats must be reduced wherever they occur, whether on nesting beaches or in feeding, migratory, or other habitats (Steering Committee, Bellagio Conference on Sea Turtles 2004; Bellagio report 2007; Wallace et al. 2011, 2013); a holistic approach that addresses threats at all life history stages needs to be implemented (Dutton and Squires 2011).
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|Citation:||Tiwari, M., Wallace, B.P. & Girondot, M. 2013. Dermochelys coriacea (Southwest Atlantic Ocean subpopulation). The IUCN Red List of Threatened Species 2013: e.T46967838A46967842.Downloaded on 24 February 2018.|