|Scientific Name:||Dermochelys coriacea (Southeast Atlantic Ocean subpopulation)|
|Species Authority:||(Vandelli, 1761)|
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor/s:||Tiwari, M., Wallace, B.P. & Girondot, M.|
|Reviewer/s:||Chaloupka, M.Y., Bolten, A.B., Dobbs, K., Limpus, C., Nel, R., Eckert, K.L., Mortimer, J.A., Pritchard, P.C.H., Dutton, P.H., van Dijk, P.P., Casale, P. & Miller, J.|
|Contributor/s:||Honarvar, S., Formia, A., Girard, A. & Beheret, N.|
The nesting epicenter for the Southeast Atlantic Leatherback subpopulation lies in Bioko Island, Equatorial Guinea, Gabon, and the Republic of Congo, with additional nesting in much smaller numbers extending north to Senegal and south to Angola (Turtle Expert Working Group 2007, Fretey et al. 2007a, Witt et al. 2009). Dutton et al. (2013) found that the West African rookeries sampled (Gabon and Ghana) were genetically different (mitochondrial DNA and microsatellites) from the other Atlantic rookeries and the South African rookery sampled, and that even Gabon and Ghana were fairly well differentiated based on mitochondrial DNA, but more weakly differentiated based on microsatellite data. The marine habitat for this subpopulation is thought to extend from the Atlantic coast of Africa south to the equator and southwest to Brazil, Uruguay, and Argentina and southeast to South African waters (Figure 1 in attached PDF), but the northern geographic boundaries lack resolution. Continuous long-term data sets, complete data on genetic stocks, and reliable estimates of the number of mature individuals are unavailable for this subpopulation. Furthermore, the majority of abundance in this subpopulation occurs in Gabon (TEWG 2007, Witt et al. 2009), for which long-term data are unavailable. Therefore this subpopulation is classified as Data Deficient for all applicable criteria (A, B, C, and D).
Although the geographical distribution of the Southeast and the Southwest Atlantic subpopulations are identical (Wallace et al. 2010), the two subpopulations are genetically distinct and do not exchange in breeding individuals (Dutton et al. 2013). Therefore, we assessed each subpopulation separately, and the category listing of one does not affect the listing of the other (IUCN 2012).
Criterion A could not be evaluated for this subpopulation because the majority of nesting in this subpopulation occurs in Gabon, for which trend data are unavailable. Although data were available from the other two major nesting sites (Table 1 in attached PDF), the cumulative abundance of these two sites is <10% the abundance in Gabon. Therefore, it was inappropriate to assign the trends observed in Congo and Equatorial Guinea to the entire subpopulation.
We also applied Criterion B, C, and D to the Southeast Atlantic subpopulation. The extent of occurrence and the area of occupancy exceeded the thresholds for the threatened categories, and the number of genetic stocks or “locations” has not been determined for this subpopulation. Furthermore, because available population abundance data are not sufficient to estimate number of mature individuals, Criteria C and D could not be evaluated.
Gabon hosts the largest Leatherback nesting population in the world; Witt et al. (2009) estimated 36,185-126,480 clutches per year representing 5865 – 20,499 females, and a total estimate of 15,730 to 41,373 breeding females in the population. Outside of Gabon, estimates are not available for the entire coastline of the Republic of Congo; however, the estimated mean number of Leatherback nests laid on several short stretches of beach between 2003 and 2006 was 421 and during the 2006/2007 nesting season it was 497; the number of beaches monitored varied among years (Godgenger et al. 2009). On Bioko Island, Equatorial Guinea, the mean number of nests recorded on five nesting beaches monitored on this island between 2000/2001 and 2004/2005 was 3,896 (SD = 1461.5; range = 2,127-5,071; Rader et al. 2006). Low and/or sporadic nesting is reported from many of the other countries (Fretey et al. 2007a), but in Côte d’Ivoire, nesting by Leatherbacks is quite common and 218 nests were counted over 41 km of beach in February 2001 (Gomez 2005) and in Ghana, between August 1998 and April 2000, 319 Leatherback nests were counted along a 14 km stretch (Amiteye 2000). Studies are underway in Sierra Leone, Liberia, and Angola to determine nesting numbers (M. Tiwari pers.comm.). Threats to this subpopulation include collection of eggs, harvest of females for consumption, oil exploitation activities, chemical and industrial pollution, and sand mining. However, accidental capture in fisheries is perhaps the biggest threats for Leatherbacks (e.g. Carranza et al. 2006, Witt et al. 2011, Riskas and Tiwari 2013). Leatherbacks are also integrated into traditional medicine and voodoo practices (Fretey et al. 2007b), and high poverty levels in Africa place enormous pressure on sea turtle populations and would need to be recognized and addressed by conservation and management programmes (Formia et al. 2003).
We assessed the status of the Southeast Atlantic Leatherback subpopulation by Criteria A-D; as no population viability analysis has been performed, Criterion E could not be applied.
Criterion A: We compiled available data on abundance of nesting females or their nesting activities from Gabon, Republic of Congo, and Bioko Island, Equatorial Guinea (Table 1 in attached PDF). For marine turtles, annual counts of nesting females and their nesting activities (more often the latter) are the most frequently recorded and reported abundance metric across index monitoring sites, species, and geographic regions (NRC 2010). We presented and analysed all abundance data in numbers of nests yr-1, as this metric was the most commonly available (Table 1 in attached PDF). However, the positive population trends derived from the significantly smaller populations nesting in Equatorial Guinea and Congo cannot be used to draw conclusions for this subpopulation because the vast majority of nesting abundance in this subpopulation occurs in Gabon, for which trend data are unavailable (Table 1 in attached PDF). Therefore, this subpopulation was classified as Data Deficient.
Criterion B: We defined extent of occurrence (EOO) as the total area included within the geo-referenced boundaries of the Southeast Atlantic Leatherback subpopulation (Figure 1 in attached PDF), which we calculated to be >48million km2. We defined area of occupancy (AOO) as the linear distribution of nesting sites within the EOO, multiplied by 2 km to account for the IUCN Guidelines for calculating linear AOOs using minimum grid cell size of 2 km x 2 km. The AOO for this subpopulation was calculated in excess of 2,000 km2. Complete genetic information is unavailable for this subpopulation, which prevented determination of the exact number of locations. Therefore, this subpopulation classified as Data Deficient for Criterion B.
Abundance data and reliable life history data (e.g., clutch frequency per female, re-migration intervals, sex ratios) are not available for this subpopulation to estimate the mature adult population and it is therefore classified as Data Deficient under Criterion C.
Criterion D: The number of mature individuals and the number of locations are not known for the Southeast Atlantic subpopulation (see above), and therefore it is classified as Data Deficient under Criterion D.
Sources of UncertaintyData collection began relatively recently in this subpopulation. Continuous long-term datasets are not available to determine trends and reliable life-history data are yet to be determined. For these reasons, there is high uncertainty in subpopulation abundance and trend estimates, as well as geographic boundaries, genetic population structure, and impacts of threats to the subpopulation. For further reading on sources of uncertainty in marine turtle Red List assessments, see Seminoff and Shanker (2008).
Leatherbacks are distributed circumglobally, with nesting sites on tropical sandy beaches and migratory and foraging ranges that extend into temperate and sub-polar latitudes. The nesting epicentre for the Southeast Atlantic Leatherback subpopulation lies in Bioko Island, Equatorial Guinea, Gabon, and the Republic of Congo with nesting extending in smaller numbers north to Senegal and south to Angola (Turtle Expert Working Group 2007, Fretey et al. 2007a, Witt et al. 2009). See Eckert et al. (2012) for review of Leatherback geographic range, and Fretey et al. (2007a) for a regional review.
Native:Angola (Angola); Argentina; Benin; Brazil; Cameroon; Congo; Congo, The Democratic Republic of the; Côte d'Ivoire; Equatorial Guinea (Bioko); Gabon; Gambia; Ghana; 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 – eastern central; Atlantic – northeast; Atlantic – northwest; Atlantic – southeast; Atlantic – southwest; Atlantic – western 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 Southeast Atlantic Ocean, Southwest 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 (Dutton et al. 1999) and in the Atlantic Ocean, in particular (Dutton et al. 2013), and are included within RMU delineations (Wallace et al. 2010; shapefiles can be viewed and downloaded at: http://seamap.env.duke.edu/swot).
|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).
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 this Southeast Atlantic subpopulation, accidental capture in fisheries is one of the biggest threats (e.g., Carranza et al. 2006, Witt et al. 2011, Wallace et al. 2013, Riskas and Tiwari 2013), along with harvest of eggs and females for consumption as well as for use in traditional medicine and voodoo practices, oil exploitation activities, chemical and industrial pollution as well as sand mining (Fretey et al. 2007a,b; Wallace et al. 2011). The impact of these and other threats such as predation and erosion have not been sufficiently quantified.
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, Wallace et al. 2013, Riskas and Tiwari 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). Finally, high poverty levels in Africa place enormous pressure on sea turtle populations and would need to be recognized and addressed by conservation and management programs (Formia et al. 2003).
|Citation:||Tiwari, M., Wallace, B.P. & Girondot, M. 2013. Dermochelys coriacea (Southeast Atlantic Ocean subpopulation). In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 11 March 2014.|
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