Green sea turtles

Close-up of the face of an adult green sea turtle
The only sure way to distinguish sea turtle species is by counting the scutes (plates on their carapace-the upper shell) and the scales between their eyes.  This green sea turtle has two scales between their eyes. NPS Photo.
The Green Sea Turtle
Species: Green (Chelonia mydas)
Size: Adult carapace (upper shell) length = 36-48 inches (90-122 cm) (National Marine Fisheries Service 2015, U.S. Fish and Wildlife Service 2015)
Adult weight = 300-440 pounds (135-200 kg) (National Marine Fisheries Service 2015, U.S. Fish and Wildlife Service 2015)
Coloration: Hatchlings are black above and white below, with white edges on their carapace (upper shell) and flippers; adults are mottled brown above and yellowish below with radiating markings on their carapace (upper shell)
Range: Nesting – Nesting occurs in over 80 countries. Major Atlantic Ocean nesting areas include Ascension Island, Aves Island, Costa Rica, and Surinam (National Marine Fisheries Service 2015, U.S. Fish and Wildlife Service 2015). In the Gulf of Mexico, nesting occurs in Florida and Padre Island in Texas. (Shaver 2000)
Non-nesting – Found in tropical and subtropical waters along continental coasts and islands between 30° North and 30° South worldwide (National Marine Fisheries Service 2015). In the Gulf of Mexico, juveniles occur in inshore and nearshore waters along Florida and Texas (Shaver 2000)
Diet: Hatchlings eat plants and marine invertebrates; juveniles and adults eat algae and sea grasses (U.S. Fish and Wildlife Service 2015)
Lifespan: Unknown; reach sexual maturity at 20-50 years (National Marine Fisheries Service 2015)
Status: Populations in Florida and the Pacific coast of Mexico are federally endangered; other populations are federally threatened In April 2016, the National Marine Fisheries Service revised the listing by listing eight distinct population segments as threatened and three DPS as endangered. (National Marine Fisheries Service 2015)
Nesting season: Generally June-September in the U.S.; females nest every 1-4 years and can lay 1-7 clutches in one nesting season; each nest contains an average of 136 eggs that take about 2 months to hatch (National Marine Fisheries Service and U.S. Fish and Wildlife Service 1991,U.S. Fish and Wildlife Service 2015)
Historic population: Unknown
Lowest population: Unknown
Current population: The two largest nesting aggregations worldwide currently include Tortuguero, Costa Rica with about 30,052-64,396 females nesting annually and Raine Island, Australia with 4,000- 89,000 females nesting annually. The estimated nester abundance in Florida is 8,426 (National Marine Fisheries Service 2015)
Population trends: The Marine Turtle Specialist Group examined trends at 32 nesting sites around the world and found a 48-65% decline in the number of mature females nesting annually over the past 100-150 years. Nesting has increased substantially in Mexico, Costa Rica, and Florida (National Marine Fisheries Service 2015)
Reasons for decline: Historic overharvest of eggs, juveniles, and adults; historic and ongoing incidental capture in fishing gear (National Marine Fisheries Service 2015); historic and ongoing loss of juveniles during sudden, extreme cold weather events (Shaver et. al. 2017).
Current threats: Incidental capture in fishing gear; harvest of eggs, juveniles, and adults; fibropapillomatosis (disease); degradation of marine and nesting habitats (National Marine Fisheries Service 2015); ongoing loss of juveniles during sudden, extreme cold weather events (Shaver et al. 2017).

FUN AND FASCINATING FACTS about the Green:
  • A sea turtle vegetarian! Hatchlings eat both plants and marine invertebrates, but once they reach juvenile age, greens are the only sea turtles that are strictly herbivores (plant-eaters). They feed on algae and sea grasses. In fact, the turtle grass, found in the Laguna Madre gets its name because it is a favorite food of green sea turtles.
  • A nesting roller coaster! Similar to other sea turtle species, female green sea turtles typically do not nest every year. In any given year, only a portion of the females come ashore to nest. While that portion varies each year, it varies a lot more for the green than for other species. Green sea turtle nesting populations have a very strong, alternating nesting pattern and can vary from year to year. In a major green nesting area like Florida, the number of nests found in a year can fluctuate from 1,500 one year to 200 the following year.
  • What’s in a name? The green sea turtle is brown, not green! So why was it named the green sea turtle? Its name comes not from its coloration but from the greenish color of its fat.
  • A hot spot for Generation Next! Padre Island and the adjacent Laguna Madre provide one of just a few places in the western Gulf of Mexico where juvenile green sea turtles live as they grow up! Sunlight can reach the bottom of the bay’s shallow waters. This allows growth of large beds of tasty sea grasses that green sea turtles eat. They also find algae to eat among the large rocks that line the jetties in the area.
  • Waiter, there’s a turtle in my soup! Culinary appeal is the primary reason for the decline of the green sea turtle. Green turtle soup was once a popular dish. Introduced to England as a luxury food in the 18th century, dishes made with green turtles became very popular. By 1879, about 15,000 turtles were imported annually by England. Cuba was also a major importer. Green turtle harvest and canning industries sprang up along the Florida and Texas coasts, including in Corpus Christi. As a result of overharvest and severe cold weather events caused green turtle numbers to plunge and led to the demise of the fishery in the 1890s (Rothschild 2004).
  • This order is to go! The green turtle was once an important food source for the British Royal Navy. Ships made scheduled stops to acquire live green sea turtles on board as living provisions that the sailors would eat during their voyage (Rothschild 2004, Woods Hole Oceanographic Institution 2013).
  • Is it cold out there or is it me? Like all reptiles, green sea turtles are ectothermic (cold blooded) and are affected by surrounding temperatures. During winter, young greens living around Padre Island are vulnerable to sudden, extreme cold weather events. Turtles enter the shallow waters of the Laguna Madre to feed on sea grasses. Unfortunately, for turtles, shallow water can change temperature quickly. A gradual drop in temperatures allows time for turtles to swim from shallow bays into deeper, warmer waters of the Gulf of Mexico; however, a sudden, extreme drop in temperatures may render a sea turtle immobile. If a sudden drop in temperature occurs, the turtle becomes “cold stunned” and can no longer swim or move. The helpless turtle floats at the mercy of the currents and can wash ashore. If not rescued, cold stunned turtles often succumb to exposure or predation.
  • All hands on deck! When sudden, severe cold weather events occur along the South Texas coast, the Division of Sea Turtle Science and Recovery at Padre Island National Seashore takes a leading role searching for and rescuing cold stunned sea turtles. Park staff and volunteers survey the Laguna Madre, rescuing cold stunned sea turtles. Other federal agencies, state agencies, and nonprofit organizations are essential partners playing major roles every year. Sometimes hundreds, even thousands of green turtles are rescued during a single cold stunning event.
  • Turtles, turtles everywhere! What do you do with 800 or more cold stunned sea turtles? Rescued turtles are taken to specially designated, temporary holding facilities operated by partners. Once Gulf of Mexico or bay waters have risen to safe temperatures and the individual turtles have recovered from hypothermia, the turtles are released into the wild. When conditions allow, the public is often invited to watch the turtle releases. Public cold stunned turtle releases occur periodically and do not occur every year.
  • Recent developments…. In recent years, the number of cold stunned green sea turtles found along the South Texas coast has increased significantly. Not all cold stunned sea turtles survive, although most do if rescued quickly. The increase in cold stunned green turtles strongly suggests the number of young green sea turtles has increased significantly in recent years, and that is good news for the future prospects green sea turtles.

Literature Cited:
Institution, Woods Hole Oceanographic. 2013. Oceanus (Vol. 21). London: Forgotten Books. (Original work published pre-1945, year unknown)
National Marine Fisheries Service. 2015. Green Sea Turtle (Chelonia mydas) species page. Retrieved from http://www.nmfs.noaa.gov/pr/species/turtles/green.htm
National Marine Fisheries Service and U.S. Fish and Wildlife Service. 1991. Recovery Plan for U.S. Population of Atlantic Green Turtle. National Marine Fisheries Service, Washington, D.C.
Rothschild, S.B. 2004. Beachcomber’s Guide to Gulf Coast Marine Life: Texas, Louisiana, Mississippi, Alabama, and Florida. Third Edition.
Shaver, D.J. (2000). Donna Shaver, Distribution, Residency, and Seasonal Movements of the Green Sea Turtle, Chelonia Mydas (Linnaeus, 1758), In Texas, PH. D. Dissertation. Texas A&I University, 2000. 273 pages.
Shaver DJ, Tissot PE, Streich MM, Walker JS, Rubio C, Amos AF, et al. (2017) Hypothermic stunning of green sea turtles in a western Gulf of Mexico foraging habitat. PLoS ONE 12(3): e0173920.
U.S. Fish and Wildlife Service. 2015. Green Sea Turtle (Chelonia mydas) species profile. Retrieved from http://www.ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=C00S

Last updated: December 4, 2018

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