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Loggerhead

Caretta caretta

 

Loggerhead sea turtles, known for their distinctive large head and powerful jaws, inhabit tropical to temperate regions worldwide (1).  Early juvenile loggerheads lead a pelagic existence, while adults inhabit the neritic zone but migrate thousands of miles to foraging, breeding, and nesting grounds (2,3)  Eighty-eight percent of loggerhead nesting activity occurs in Oman, Australia and the southeastern coast of the United States.  Smaller aggregations are found along the coasts of Brazil, the eastern Mediterranean and the Cape Verde Islands (1).  Many nesting populations are in decline; for example, the Pacific nesting population has decreased 80% in recent decades (1,4 and 5 in 6).  Loggerheads are a CITES Appendix I species, and are listed as endangered by the World Conservation Union (7,8)  They are currently listed as threatened under the Endangered Species Act in the United States, though Oceana and the Center for Biological Diversity have filed a petition for the U.S. government to designate western North Atlantic loggerheads as a distinct population segment and reclassify them as endangered (9).

 

The incidental capture of loggerheads in fishing gear has been a leading factor in their decline, and remains a significant threat to long-term population stability (1).  Depending on their location and life history stage, loggerheads may encounter a variety of fisheries, including trawls, gillnets, pelagic longlines, setnets, dredges, traps, pots, weirs, and pound nets (1,10).  Individuals may be hooked while attempting to swallow bait (11), trapped in nets, or entangled in buoys, trap lines, or discarded fishing gear (12).  Interactions with fishing gear often results in serious injury or death by drowning.  Large-scale trawl, longline, and gillnet fisheries are considered to pose the most significant bycatch threat (1,12)   Pelagic longlines targeting tuna and swordfish captured an estimated 200,000 loggerheads in 2000 alone (13)  However, substantial and often undocumented bycatch in small-scale coastal fisheries may pose an even greater risk, particularly where heavy fishing effort coincides with developmental and foraging grounds (14,15).

 

Bycatch mitigation efforts typically focus on industrial fisheries as a consequence of their large scale, oversight by regional fishery management organizations, and documentation and direct observation of bycatch interactions (6,15)  Longline bycatch can be reduced by substituting circle hooks for J hooks and using squid rather than fish for bait.  The post-release survival rate of hooked turtles can be maximized with careful handling and release procedures (11,16,17).   Loggerheads are more likely to encounter shallow-set longlines targeting swordfish than deeper sets targeting tuna, and eliminating shallow sets would likely reduce longline bycatch as well (18 in 6,19).  Trawl bycatch can be reduced with the use of a Turtle Exclude Device (TED), a metal grate which diverts turtles away from a net while allowing shrimp or fish to pass through (20).  TEDs were developed in the U.S. in the late 1970s, and have been required year-round in the southeast shrimp trawl fishery since 1994 (21)  Trawl mortality also can  be reduced by shortening the duration of each tow (22 in 23). 

 

Loggerheads often forage and migrate in association with major ocean currents and gyre systems (21,24).  Communication between fleets, as well as predictive and responsive time or area-based closures, can help reduce fishing pressure in areas where loggerheads are likely to aggregate (16,24).  However, bycatch mitigation is particularly difficult in artisanal fisheries, which typically lack centralized management plans and credible enforcement (15).  Promising strategies have focused on community level co-management, awareness campaigns, and the development of ecotourism opportunities and other economic alternatives (15,25).

 

 

References and additional resources:

1.  NOAA. NMFS. Office of Protected Resources. Loggerhead Turtle (Caretta caretta).  http://www.nmfs.noaa.gov/pr/species/turtles/loggerhead.htm  Downloaded 31 December 2007.

 2.  Bjorndal, K.A. 1997. Foraging Ecology and Nutrition of Sea Turtles.  Pages 199-231 in P.L. Lutz and J.A. Musick, editors. The Biology of Sea Turtles.  Washington, D.C.: CRC Press

 3.  Plotkin, P. 2003. Adult Migrations and Habitat Use.  Pages 225-241 in P.L. Lutz, J.A. Musick and J. Wyneken, editors. The Biology of Sea Turtles, Volume II.  Washington, D.C.: CRC Press

 4.  Kamezaki, N., K. Matsuzawa, O. Abe, H. Asakawa, T. Fujii, K. Goto et al 2003.  Loggerhead turtles nesting in Japan. Pages 210-217 in A.B. Bolten and B.E. Witherington, editors. Loggerhead sea turtles. Smithsonian Institute Press, Washington, D.C.

5.  Limpus, C. and D. J. Limpus. 2003. The loggerhead turtle, Caretta caretta, in the Equatorial and Southern Pacific Ocean: a species in decline.  Pages 199–209 in A. B. Bolten and B. E.Witherington, editors. Loggerhead sea turtles. Smithsonian Institution Press, Washington,  D.C.

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

 7.  IUCN 2007. 2007 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 31 December 2007.

 8.  Convention on International Trade in Endangered Species of Wild Fauna and Flora. CITES Species Database.  http://www.cites.org/eng/resources/species.html  Downloaded 15 January 2008.

 9.  Oceana and the Center for Biological Diversity. 2007. Petition Pursuant to the Endangered Species Act to Designate the Western North Atlantic Subpopulations of the Loggerhead Sea Turtle (Caretta caretta) as a Distinct Population Segment and to Reclassify the Western North Atlantic Subpopulation as Endangered. http://www.nmfs.noaa.gov/pr/pdfs/species/petition_north_atlantic_loggerhead.pdf Downloaded 22 January 2008.

10.  Báez, J.C., R. Real, C. García-Soto, J.M. de la Serna, D. Macías, and J.A. Camiñas. 2007.  Loggerhead turtle by-catch depends on distance to the coast, independent of fishing effort:  Implications for conservation and fisheries management. Marine Ecology Progress Series 338: 249-256

 11.  Read, A.J. 2007.  Do circle hooks reduce the mortality of sea turtles in pelagic longlines? A review of recent experiments. Biological Conservation 135: 155-169

 12.  IUCN/SSC Marine Turtle Specialist Group. K.L. Eckert, K.A. Bjorndal, F.A. Abreu-Grobois and M. Donnelly, editors. 1999. Research and Management Techniques for the Conservation of Sea Turtles.  http://www.iucn-mtsg.org/publications/Tech_Manual/Tech_Manual_en/06%20Pritchard&Mortimer.pdf  Downloaded 15 January 2008

 13.  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

 14.  Koch, V., W.J. Nichols, H. Peckham and V. de la Toba. 2006. Estimates of sea turtle mortality from poaching and bycatch in Bahía Magdalena, Baja California Sur, Mexico. Biological Conservation 128: 327-344

 15.  Peckham, S.H., D.M. Diaz, A. Walli, G. Ruiz, L.B. Crowder and W.J. Nichols. 2007. Small-scale fisheries bycatch jeopardizes endangered Pacific loggerheads. PloS ONE 2 (10)

 16.  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

 17.  Watson, J.W., S.P. Epperly, A.K. Shah, and D.G. Foster. 2005. Fishing methods to reduce sea turtle mortality associated with pelagic longlines. Canadian Journal of Fisheries and Aquatic Science 62: 965-981

 18.  NMFS 2004. Biological opinion on the authorization of pelagic fisheries under the Fisheries management plan for the pelagic fisheries of the Western Pacific Region.  NMFS, Honolulu, Hawaii

 19.  Polovina, J.J., G.H.Balazs, E.A. Howell, D.M. Parker, M.P. Seki, and P.H. Dutton. 2004. Forage and migration habitat of loggerhead (Caretta caretta) and olive ridley (Lepidochelys olivacea) sea turtles in the central North Pacific Ocean. Fisheries Oceanography 13 (1): 36-51

 20.  Lewison, R.L., L.B. Crowder and D.J. Shaver. 2003. The impact of turtle excluder devices and fisheries closures on loggerhead and Kemp’s ridley strandings in the western Gulf of Mexico. Conservation Biology 17 (4): 1089-1097

 21.  Lutcavage, M.E., P. Plotkin, B. Witherington and P.L. Lutz. 1997. Human Impacts on Sea Turtle Survival. Pages 387-409 in P.L. Lutz and J.A. Musick, editors.  The Biology of Sea Turtles.  Washington, D.C.: CRC Press

 22.  Henwood, T.A. and W.E. Stuntz. 1987. Analysis of sea turtle captures and mortalities during commercial shrimp trawling. Fisheries Bulletin 85: 813-817

 23.  Epperly, S.P. 2003. Fisheries-Related Mortality and Turtle Excluder Devices (TEDs). Pages 339-353 in P.L. Lutz, J.A. Musick and J. Wyneken, editors.  The Biology of Sea Turtles, Volume II.  Washington, D.C.:  CRC Press

 24.  Hawkes, L.A., A.C. Broderick, M.S. Coyne, M.H. Godfrey and B.J. Godley. 2007. Only some like it hot – quantifying the environmental niche of the loggerhead sea turtle. Diversity and Distributions 13: 447-457

 25.  Weir, C.R., T. Ron, M. Morais and A.D.C. Duarte. 2007. Nesting and at-sea distribution of marine turtles in Angola, West Africa , 2000-2006: Occurrence, threats and conservation implications. Oryx 41 (2): 224-231