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Green Sea Turtle (Chelonia mydas)

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Green turtles are the largest of all the hard-shelled sea turtles, but have a comparatively small head.
Adult green turtles are unique among sea turtles in that they eat only plants; they are herbivorous, feeding primarily on seagrasses and algae. This diet is thought to give them greenish-colored fat, from which they take their name.
While nesting season varies from location to location in the southeastern U.S., females generally nest in the summer between June and September; peak nesting occurs in June and July. During the nesting season, females nest at approximately two-week intervals. They lay an average of five nests, or “clutches.” In Florida, green turtle nests contain an average of 135 eggs, which will incubate for approximately 2 months before hatching.

Taxonomy

Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Family: Cheloniidae
Genus: Chelonia
Species: mydas

Species Description

Weight: Adults: 300-350 pounds (135-150 kg)
Hatchlings: 0.05 pounds (25 g)
Length: Adults: 3 feet (1 m)
Hatchlings: 2 inches (50 mm)
Appearance: top shell (carapace) is smooth with shades of black, gray, green, brown, and yellow; their bottom shell (plastron) is yellowish white
Lifespan: unknown, but sexual maturity occurs anywhere between 20-50 years
Diet: seagrasses and algae
Behavior: females return to the same beaches where they were born (“natal” beaches) every 2-4 years to lay eggs, generally in the summer months

Habitat

Green turtles primarily use three types of habitat:

  • beaches for nesting
  • open ocean convergence zones
  • coastal areas for “benthic”feeding

Adult females migrate from foraging areas to mainland or island nesting beaches and may travel hundreds or thousands of kilometers each way. After emerging from the nest, hatchlings swim to offshore areas, where they are believed to live for several years, feeding close to the surface on a variety of pelagic plants and animals. Once the juveniles reach a certain age/size range, they leave the pelagic habitat and travel to nearshore foraging grounds. Once they move to these nearshore benthic habitats, adult green turtles are almost exclusively herbivores, feeding on sea grasses and algae.

Distribution

The green turtle is globally distributed and generally found in tropical and subtropical waters along continental coasts and islands between 30° North and 30° South. Nesting occurs in over 80 countries throughout the year (though not throughout the year at each specific location). Green turtles are thought to inhabit coastal areas of more than 140 countries.

In U.S. Atlantic and Gulf of Mexico waters, green turtles are found in inshore and nearshore waters from Texas to Massachusetts, the U.S. Virgin Islands, and Puerto Rico. Important feeding areas in Florida include the Indian River Lagoon, the Florida Keys, Florida Bay, Homosassa, Crystal River, Cedar Key, and St. Joseph Bay.

In the eastern North Pacific, green turtles have been sighted from Baja California to southern Alaska, but most commonly occur from San Diego south. In the central Pacific, green turtles occur around most tropical islands, including the Hawaiian Islands. Adult green turtles that feed throughout the main Hawaiian Islands undergo a long migration to French Frigate Shoals in the Northwest Hawaiian Islands, where the majority of nesting and mating occurs.

Population Trends

The two largest nesting populations are found at:

  • Tortuguero, on the Caribbean coast of Costa Rica, where 22,500 females nest per season on average
  • Raine Island, on the Great Barrier Reef in Australia, where 18,000 females nest per season on average

In the U.S., green turtles nest primarily along the central and southeast coast of Florida where an estimated 200-1,100 females nest annually.

Threats

  • harvest of eggs and adults (historically, though the practice continues in some areas of the world)
  • incidental capture in fishing gear
  • fibropapillomatosis (disease)

The principal cause of the historical, worldwide decline of the green turtle is long-term harvest of eggs and adults on nesting beaches and juveniles and adults on feeding grounds. These harvests continue in some areas of the world and compromise efforts to recover this species.

Incidental capture in fishing gear, primarily in gillnets, but also in trawls, traps and pots, longlines, and dredges is a serious ongoing source of mortality that also adversely affects the species’ recovery.

Green turtles are also threatened, in some areas of the world, by a disease known as fibropapillomatosis (FP).

Conservation Efforts

The highly migratory behavior of sea turtles makes them shared resources among many nations. Thus, conservation efforts for sea turtle populations in one country may be jeopardized by activities in another. Protecting sea turtles on U.S. nesting beaches and in U.S. waters alone, therefore, is not sufficient to ensure the continued existence of the species.

Sea turtles are protected by various international treaties and agreements as well as national laws:

  • CITES: listed in Appendix I of the Convention on International Trade in Endangered Species of Wild Flora and Fauna, which prohibits international trade
  • CMS: listed in Appendices I and II of the Convention on Migratory Species and are protected under the following auspices of CMS:
  • SPAW: protected under Annex II of the Specially Protected Areas and Wildlife Protocol of the Cartagena Convention
  • IAC: The U.S. is a party of the Inter-American Convention for the Protection and Conservation of Sea Turtles, which is the only international treaty dedicated exclusively to marine turtles

In the U.S., NOAA Fisheries(NMFS) and the U.S. Fish and Wildlife Service (USFWS) have joint jurisdiction for sea turtles, with NOAA having the lead in the marine environment and USFWS having the lead on the nesting beaches. Both federal agencies, along with many state agencies and international partners, have issued regulations to eliminate or reduce threats to sea turtles, while working together to recover them.

In the Atlantic and Gulf of Mexico, we have required measures to reduce sea turtle bycatch in pelagic longline, mid-Atlantic gillnet, Chesapeake Bay pound net, and southeast shrimp and flounder trawl fisheries, such as

  • gear modifications
  • changes to fishing practices
  • time/ area closures

NOAA Fisheries have worked closely with the shrimp trawl fishing industry to develop turtle excluder devices (TEDs) to reduce the mortality of sea turtles incidentally captured in shrimp trawl gear. TEDs that are large enough to exclude even the largest sea turtles are now required in shrimp trawl nets. Since 1989, the U.S. has prohibited the importation of shrimp harvested in a manner that adversely affects sea turtles. The import ban does not apply to nations that have adopted sea turtle protection programs comparable to that of the U.S. (i.e., require and enforce the use of TEDs) or to nations where incidental capture in shrimp fisheries does not present a threat to sea turtles (for example, nations that fish for shrimp in areas where sea turtles do not occur). The U.S. Department of State is the principal implementing agency of this law, while we serve as technical advisor. We provide extensive TED training throughout the world.

We are also involved in cooperative gear research projects designed to reduce sea turtle bycatch in the Gulf of Mexico and Atlantic pelagic longline fisheries, the Hawaii-based deep set longline fishery, the Atlantic sea scallop dredge fishery, the Chesapeake Bay pound net fishery, and non-shrimp trawl fisheries in the Atlantic and Gulf.

-TSF-

#turtles #tortoises #terrapins #seaturtles #GreenSeaTurtles #TSF

 
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