Endangered Species Of Leatherback Sea Turtle: The Threats Of Climate Changes And Fisheries To Leatherback Turtles
Only 7 species in 2 families of sea turtles survived in the entire world (Xia et al. 2008). The leatherback turtle (Dermochelys coriacea) is the largest of the turtle and is found around the world's oceans, specializing on a diet of gelatinous plankton such as jellyfish and tunicates (Bleakney 1965). Leatherback turtle's habitat range extends from tropical nesting areas to marine foraging areas spread from tropics to cool temperate waters (Goff and Lien 1988). Leatherback turtles share many their biological features with the hard-shelled turtles, they also are characterised by a number of unique features (Hamann et al. 2006). In addition, leatherback turtle can be regarded as a warm-blood reptile who can maintain a core body temperature well above that of the surrounding waters (Frair et al. 1972; Standora et al. 1984). Due to this factor, leatherback turtle is able to remain functional in the very cold waters that it encounters during deep dives and during migrations to high latitudes (Hamann et al. 2006).
However, populations of leatherbacks have declined drastically in recent years (Kaplan 2005). In response to the declines, leatherbacks have been listed as endangered species in the international endangered species list (Xia et al. 2008). The international community has paid much attention to their conservation, set up Marine Turtle Specialist Group (MTSG), established international organizations of wide influence and held international conferences regularly to find approaches for action of recue them globally (Xia et al. 2008).
In this paper, it will describe two possible causes of the decline in leatherback turtle's populations: 1) bycatch by fishing and the coastal harvest of eggs and females on and near nesting beaches; 2) climate change impacts upon the mortality of leatherback turtle. And then go on to discuss how we can protect this endangered species depending on international effort.
Global Distribution And Abundance
Leatherback turtles are capable of tolerating a wide range of water temperature and have the most extensive geographic range of any reptile species. They are nesting on beaches of the Indian, Pacific, and Atlantic Oceans in tropical and subtropical areas. None of leatherbacks often occur in high latitude waters in summer and occasionally in inshore waters (Goff and Lien 1988). Important Nesting areas include Malaysia, Pacific coast of Mexico and Central America, and Atlantic shore of northern South America.
The largest population of leatherback turtles are located in French Guiana and Suriname in South America and Gabon in Africa. Nesting also occurs throughout the Caribbean and Brazil. Florida is the only state known to support a significant number of nests (Calleson et al. 1998).
New data regarding leatherback turtle distribution continues to be gathered through a number of tagging methods (i.e., flipper tagging, internal Passive Integrated Transponder (PIT) tags and satellite tagging). Through flipper tagging, leatherbacks from the western Atlantic population have been recorded off west Africa, in the Gulf of Mexico and on the Atlantic coast of the U.S. (Pritchard 1976). Leatherbacks tagged in French Guiana have been captured in the northeast Atlantic off the coast of France, Spain and Morocco, less than 12 months after nesting (Girondot & Fretey 1996). Through satellite tracking, more studies of leatherback distribution and migration have been undertaken (Morreale et al. 1996; Hughes et al. 1998).
It was estimated that 115,000 breeding females worldwide (Pritchard 1982). However, some scientists believed that this figure may have been changed. A study incorporating information from 28 nesting beaches throughout the world estimated the population of nesting female leatherbacks worldwide at 34,500, with the majority of leatherbacks occurring in the Atlantic Ocean; the lower limit was 26,200 and the upper limit was 42,900 (Spotila et al. 1996). In 2000, Spotila estimated total adult population of female leatherbacks in the eastern Pacific at 1,690 and concluded that leatherbacks were on the edge of extinction in the Pacific Ocean. For example, there were 3103 leatherbacks nesting at Terengganu, Malausia in 1968, 200 turtles in 1980, and only 2 in 1994 (Chan & liew 1996).
The largest leatherback rookery in the western Atlantic remains along the northern coast of South America in French Guiana and Suriname, and the nesting population has been declining since 1992 (Chevalier & Girondot 1998). Recent information suggests that western Atlantic population declined from 18,800 nesting females in 1996 to 15,000 nesting females by 2000 (Spotila et al. 2000)
In Spotila's paper 2000, he argued that the decline has occurred in recent years. There are many known (and probably unknown) threats to leatherbacks.
Threats To Leatherback Turtles
Numerous threats to the leatherback have contributed to its endangered status. The mortality rate of hatchlings due to predation is high, though once they reach adult size, leatherbacks have few natural predators. Furthermore, eggs collecting and mortality associated with bycatch in longline, trawl and gillnet fisheries throughout range are the major threats to leatherback turtles (Spotila et al. 2000, Ferraroli et al. 2004, Lewison et al. 2004). Other concerns include the harvest of female leatherbacks at nesting beaches for oil and meat, nesting habitats loss, marine pollution, and the impacts of coastal development and climate change etc. (Lewison et al. 2004)
The greatest predator of the leatherbacks is, however, people. In some countries, the harvest of nesting adult females and their eggs for consumption or other uses continued to be a serious threat to leatherbacks. Because leatherbacks move very slowly on land, they are not able to defend themselves from humans on the nesting beaches. The loss of nesting adults could lead to local extinction, whereas the collection of eggs reduced the number of hatchlings available for the future recruitment. To protect eggs from harvest, a number of conservation programs have developed. While leatherback meat is considered palatable, poaching of free-swimming and nesting turtles for meat and oil does occur in some areas, including the British Virgin Islands, Dominican Republic, Jamaica, Puerto Rico and The U.S. Virgin Islands (Fleming 2001). A larger, more widespread problem is the collection of leatherback eggs for sale in local and foreign markets in the aforementioned countries (Fleming 2001).
Coastal development and the beach armouring (seawalls, revetments, riprap, sand bags, groins and sand fences) establish to protect upland structures from erosion which can interfere with access to suitable nesting sites during construction. Erosion associated with hard armouring structures also leads to the loss of nesting habitat (NMFS 1992). Soft armouring such as beach nourishment can result in beaches unsuitable for nesting due to compaction and severe scarping and may result in an altered physical nesting environment that can impact hatchling development and hatching success as well (NMFS 1992).
Artificial lighting related with coastal development, construction activities and roads can result in the disorientation of nesting females and emerging hatchlings, which result in failed nesting attempts and mortality of hatchlings. In addition, adult female turtles may avoid nesting on beaches with intense artificial lighting. When they do successfully nest on beaches, hatchlings are attracted toward the artificial light source, which disrupts their natural sea finding behaviour, resulting in stress, dehydration, and predation (Witherington 1992; Witherington & Bjorndal 1991)
The effect of marine pollution on sea turtles is not well quantified, and therefore the magnitude of pollution-related mortality is unknown. Some marine biologists argued that leatherbacks may be more susceptible to marine pollution than other turtle species due to their pelagic existence and the tendency of floating pollutants to concentrate in convergence zones that adults and juveniles use for feeding areas and migration (Lutcavage et al. 1997; Shoop & Kenney 1992).
There are many recorded cases of leatherbacks dying as a result of ingesting a variety of anthropogenic marine pollution, including plastic bags, balloons, plastic and Styrofoam pieces, tar balls, plastic sheeting, and fishing gears (Starbird 2000). Leatherbacks ingesting such materials may interfere with metabolism and gut function and lead to blockages in the digestive tract, which could result in starvation and in the absorption of toxic byproducts (Plotkin & Amos 1989).
In addition, leatherbacks are considered as an indicator of the degree of contamination of the oceanic food web, for example bio-accumulating substances such as heavy metals and polychlorinated biphenyls (PCBs) (Davenport & Wrench 1990).
Declines in the number of leatherbacks were threatened by longline swordfish and tuna fisheries of the U.S., South America, Asia, and Europe, shrimp trawl fisheries, gill net fisheries and pot fisheries throughout the world (Spotila et al. 1996; James et al. 2005). A figure showed that even with the use of larger TED to exclude leatherbacks, the offshore of U.S. commercial shrimp fishery captured nearly 640/year (NOAA/NMFS 2005). Another paper showed that mortality of leatherbacks associated with the swordfish gill net fisheries in Peru and Chile represented the major influence of mortality for East Pacific leatherbacks (Eckert & Sarti 1997). In addition, Eckert and Sarti (1997) estimated that in these countries may kill 2,000 leatherbacks annually. From 1978-1981, around 25% were leatherbacks were reported captured in the Japanese tuna longline fishery in the Atlantic (Spotila et al. 1996). During 2000, a reported paper estimated that 20,000 leatherback turtles were caught and 1,000-3,200 were killed as bycatch in Pacific longline fisheries (Lewison et al. 2004).
Global warming is predicted to have deleterious effects on marine turtles, as it could potentially influence temperature-dependent sex determination (Davenport 1997). The scientists argued that the increased hurricane activities were related to global climate change which could result in increased nesting loss due to wave erosion on leatherbacks nesting beaches. Finally, alterations in ocean current patterns may accompany climate change, therefore affecting the migration and dispersal of turtles (Davenport 1997).
Conservation And Management Needs
Basic needs are to: monitor occurrences; enforce protective regulations, for example, TED programs, regulate artisanal gill net and other fisheries, international trade restrictions and nest beach protection; conduct educational programs, particularly in Mexico, South America, Malaysia, and western Pacific; use low pressure beach lighting; keep traffic off beaches; remove nest predators if need.
Incidental bycatch in worldwide pelagic gill net, longline and trawl fisheries is the most important conservation goal. Areas where conservation efforts should be focused include the migration corridor from one area to the other (Ferraroli et al. 2004). While TED programs are required in the U.S. and encouraged in many other countries, they are hard to enforce and easy to ignore without established fisheries observer programs. Bycatch is a significant problem limiting population recovery. Scientists argued that changes in survivorship of adults and juveniles would have a greater effect on future population growth than changes at the hatchling stage (Spotila et al. 1996). Frazer (1992) emphasized the conservation of leatherbacks are needed for clean and productive marine and coastal environments. In addition, he argued that installation of TED's in shrimp trawl nets and use of low pressure sodium lighting on beaches were suggested as appropriate sea turtle conservation technologies.
Creating and maintaining the necessary conditions in efforts to achieve a viable population of leatherback turtles will be accomplished by following recovery objectives:
Objective 1: Understanding Threats. Identify and understand anthropogenic pressures to leatherback turtles.
1) Synthesize and evaluate existing data on commercial fishing activities and offshore development activities to know the impact of survival and recovery.
2) Identify and understand the level of threat to leatherback turtles from marine pollution.
3) Identify and understand other unknown activities that may pose a threat to leatherback turtles.
Objective 2: Understanding Leatherback Turtle Life History Characteristics. Support research and monitoring that will fill knowledge gaps concerning traits of leatherback turtles around the world.
1) Synthesize and evaluate existing knowledge from research and monitoring activities undertaken regarding leatherback turtles.
2) Support research on knowledge gaps identified from migration, movement behaviour, life history, distribution, and abundance.
Objective 3: Nesting Habitat Identification and Protection. Take steps to identify and protect leatherback turtles' habitat around world.
1) Carry out research to identify habitat utilized by leatherback turtles.
2) Assess the extent that significant habitat exists around world oceans.
3) Assess and evaluate approach to habitat protection.
Objective 4: Education. Implement education activities that support leatherback turtle recovery around the world.
1) Develop programmes for educating people about leatherback turtle conservation.
Objective 5: International Initiatives. Promote international initiatives contributing to the recovery of leatherback turtles.
1) Investigate options for local participation in and promotion fo international agreements and conventions that promote leatherback turtle protection and recovery.
2) Collaborate with other countries and international organization on leatherback turtle conservation initiatives if need.