Green Sea Turtle
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Green sea turtles are one of the largest and most widespread of all the marine turtles. The oval carapace varies from olive to brown, grey and black with swirls and irregular patters, but the common name is derived from the green colour of the fat and connective tissues of this species. Two subspecies are currently recognised; the Pacific green sea turtle (Chelonia mydas agassizii) tends to be smaller than its Atlantic cousin (C. m. mydas) with a narrower carapace that may sometimes be completely black, providing the other common name of 'black turtle' to certain populations. The plastron, or undershell, remains a pale yellow or orange throughout life. Males are generally smaller than females , and green sea turtles differ in appearance from other marine turtles by the possession of a single pair of scales in front of the eyes and a serrated bottom jaw. The tiny black hatchlings are only around 50 millimetres long.
Green sea turtles are found in tropical and portions of subtropical oceans worldwide. They are found in the Atlantic Ocean from the eastern United States along coastal South America to South Africa. They are found throughout the Caribbean Sea and portion of the Mediterranean. They are also found throughout the warm waters of the Indian and Pacific Oceans.
Biogeographic Regions: Indian Ocean (Native ); Atlantic Ocean (Native ); Pacific Ocean (Native ); Mediterranean Sea (Native )
Habitat and Ecology
Like most sea turtles, green sea turtles are highly migratory and use a wide range of broadly separated localities and habitats during their lifetimes (for review see Hirth 1997). Upon leaving the nesting beach, it has been hypothesized that hatchlings begin an oceanic phase (Carr 1987), perhaps floating passively in major current systems (gyres) that serve as open-ocean developmental grounds (Carr and Meylan 1980, Witham 1991). After a number of years in the oceanic zone, these turtles recruit to neritic developmental areas rich in seagrass and/or marine algae where they forage and grow until maturity (Musick and Limpus 1997). Upon attaining sexual maturity green sea turtles commence breeding migrations between foraging grounds and nesting areas that are undertaken every few years (Hirth 1997). Migrations are carried out by both males and females and may traverse oceanic zones, often spanning thousands of kilometers (Carr 1986, Mortimer and Portier 1989). During non-breeding periods adults reside at coastal neritic feeding areas that sometimes coincide with juvenile developmental habitats (e.g., Limpus et al. 1994, Seminoff et al. 2003).
Green sea turtles are an endangered species because they have so many predators--including humans. Even though a female can lay over 200 eggs in on clutch, some will not hatch, and many will be eaten. Even if they do hatch, they get eaten on their way to the water, and in the water. So only a few will survive, if any. If they do survive, they can live to be over 100 years old. Sometimes eggs are laid on a public beach. When this happens, conservationists come and move them to a safer place. In the United States, green sea turtles are protected by the Endangered Species Act.
Green sea turtles, like other sea turtle species, are particularly susceptible to population declines because of their vulnerability to anthropogenic impacts during all life-stages: from eggs to adults. Perhaps the most detrimental human threats to green sea turtles are the intentional harvests of eggs and adults from nesting beaches and juveniles and adults from foraging grounds. Unfortunately, harvest remains legal in several countries despite substantial subpopulation declines (e.g., Humphrey and Salm 1996, Fleming 2001, Fretey 2001). In addition, a number of incidental threats impact green sea turtles around the world. These threats affect both terrestrial and marine environments, and include bycatch in marine fisheries, habitat degradation at nesting beaches and feeding areas, and disease. Mortality associated with entanglement in marine fisheries is the primary incidental threat; the responsible fishing techniques include drift netting, shrimp trawling, dynamite fishing, and long-lining. Degradation of both nesting beach habitat and marine habitats also play a role in the decline of many Green Sea Turtle stocks. Nesting habitat degradation results from the construction of buildings, beach armoring and re-nourishment, and/or sand extraction (Lutcavage et al. 1997). These factors may directly, through loss of beach habitat, or indirectly, through changing thermal profiles and increasing erosion, serve to decrease the quantity and quality of nesting area available to females, and may evoke a change in the natural behaviors of adults and hatchlings (Ackerman 1997). The presence of lights on or adjacent to nesting beaches alters the behavior of nesting adults (Witherington 1992) and is often fatal to emerging hatchlings as they are attracted to light sources and drawn away from the water (Witherington and Bjorndal 1990). Habitat degradation in the marine environment results from increased effluent and contamination from coastal development, construction of marinas, increased boat traffic, and harvest of nearshore marine algae resources. Combined, these impacts diminish the health of coastal marine ecosystems and may, in turn, adversely affect green turtles. For example, degradation of marine habitats has been implicated in the increasing prevalence of the tumor-causing Fibropapilloma disease (George 1997).
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