Leatherback

Leatherback, Dermochelys coriacea

Leatherbacks are the most widely distributed sea turtle species and span tropical to sub-arctic waters worldwide.   Listed as a CITES Appendix I species since 1977, they are classified as critically endangered under the IUCN’s Red List of Threatened Species (1,2).  Over the past 25 years, the world population of leatherbacks has declined by more than two-thirds to an estimated 34,500 nesting females (1,3).  Eastern Pacific leatherbacks are at the highest risk of extinction, and nesting leatherback populations have drastically declined in Mexico and Costa Rica (4,5). In the Western Pacific, the Malaysian leatherback population has been extirpated, and remaining populations in Indonesia and Papua New Guinea continue to be at risk (3,4,6).  Leatherbacks are also rare in the Indian Ocean, where nesting populations in Sri Lanka and India were already in steep decline by the mid-twentieth century (3,5).  Atlantic leatherbacks have fared better in recent decades with smaller nesting populations on the rise in the Caribbean and in South Africa.  The world’s largest leatherback nesting populations in French Guiana and Surinam are considered stable or increasing (1,3,5,7)

Bycatch interactions are presumed to be one of the most significant causes of leatherback population declines (5,8). Adult leatherbacks are frequently hooked or entangled by pelagic longliners targeting tuna, mahi mahi, and swordfish.  While bycatch rates are low, the cumulative pressure of industrial pelagic longlining is thought to have an enormous impact on leatherback populations worldwide (9,10).  In 2000, high-seas longlining fleets of 40 nations set an estimated 1.4 billion hooks, catching an estimated 50 to 60,000 leatherbacks (9). Although the mortality rate of hooked or entangled leatherbacks is estimated to be only 4-27%, individuals may be injured during release or even harvested intentionally (10). Strategies for reducing longline bycatch include regulatory solutions, modifications to fishing gear and fishing techniques , improved communication between fleets, improved handling techniques, and fishing area closures (11) 

Leatherbacks are also likely to encounter gillnets and trawls in coastal waters, particularly off the coasts of South and Central America (12). Bycatch mortality rates of sea turtles are often highest in gillnets and trawls, and these coastal fisheries may be responsible for a greater proportion of leatherback bycatch mortality than longlines (10).  Reproductive females are particularly susceptible to interactions with inshore fishing gear during the nesting season (6). Other coastal hazards to leatherback populations include egg collection and predation, pollution, degradation of nesting habitat, and direct harvest of adults (9,10,12)

Conservation strategies could focus on the protection of migration corridors and hotspots, areas of high concentrations of leatherbacks that could  put entire leatherback populations at risk (8,11,13). However, the stability of leatherback populations depends on high survivorship throughout all life stages (3). Even if longline mortality is significantly reduced, failure to mitigate the impact of coastal fisheries and shore-based threats will not provide long-term protection to declining populations (10,12). Effective conservation strategies will require coordinated international action to protect vulnerable individuals both at land and at sea, and across entire ocean basins (1,4,8,9,10,14).

References and additional resources:

1.  Sarti Martinez, A.L. 2000. Dermochelys coriacea. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 21 August 2007.

2.  UNEP-WCMC. 5 September, 2007. UNEP-WCMC Species Database: CITES-Listed Species

3.  Spotila, J.R., A.E. Dunham, A.J. Leslie, A.C. Steyermark, P.T. Plotkin, and F.V. Paladino.  1996.  Worldwide population decline of Dermochelys coriacea:  Are leatherback turtles going extinct?  Chelonian Conservation and Biology 2(2): 209-222

4.  Crowder, L.  2000.  Leatherback’s survival will depend on an international effort.  Nature 405: 881

5.  Spotila, J.R., R.D. Reina, A.C. Steyermark, P.T. Plotkin, and F.V. Paladino.  2000.  Pacific leatherback turtles face extinction.  Nature 405:  529-530 

6.  Chan, E. and H. Liew.  1996.  Decline of the leatherback population in Terngganu, Malaysia, 1956-1995.  Chelonian Conservation and Biology 2(2): 196-203

7.  Dutton, D.L., P.H. Dutton, M. Chaloupka, and R.H. Boulon.  2005.  Increase of a Caribbean leatherback turtle Dermochelys coriacea linked to long-term nest protection.  Biological Conservation 126: 186-194

8.  Ferraroli, S., J. Georges, P. Gaspar, and Y. Le Maho. 2004.  Where leatherback turtles meet fisheries.  Nature 429: 521

9.  Lewison, R.L., S.A. Freeman and L.B. Crowder.  2004.  Quantifying the effects of fisheries on threatened species:  the impact of pelagic longlines on loggerhead and leatherback sea turtles.  Ecology Letters 7: 221-231

10.  Lewison, R.L. and L.B. Crowder.  2007.  Putting longline bycatch of sea turtles into perspective.  Conservation Biology 21 (1): 79-86

11.  Gilman, E., E. Zollett, S. Beverly, H. Nakano, K. Davis, D. Shiode, P. Dalzell, and I. Kinan.  2006.  Reducing sea turtle by-catch in pelagic longline fisheries.  Fish and Fisheries 7: 2-23

12.  Kaplan, I.C.  2005.  A risk assessment for Pacific leatherback turtles (Dermochelys coriacea).  Canadian Journal of Fisheries and Aquatic Science 62: 1710-1719

13.  Morreale, S.J., E.A. Standora, J.R. Spotila, and F.V. Paladino.  1996.  Migration corridor for sea turtles.  Nature 384: 319-320

14.  Hays, G.C., J.D.R. Houghton, and A.E. Myers.  2004.  Pan-Atlantic leatherback turtle movements.  Nature 429: 522