Green Turtle (Chelonia mydas)

Identification

 Ryan Welsh/ Inwater Research Group

Ryan Welsh/ Inwater Research Group

If you have ever been fishing, diving or boating in the coastal waters off Florida’s coastline and noticed a sea turtle, odds are it was a Green Turtle (Chelonia mydas).  Despite its name, green turtles are typically more of a olivey-brown than green, its name originating from the greenish hue found in the turtle’s fatty tissues.  Green turtles are recognized to exist in four distinct life stages: Hatchling, Juvenile, Subadult and Adult.  Ranging in size from hatchlings that weigh 1 ounce to adults that can weight up to 500 lbs, green turtles change in appearance as the grow.  At all stages, green turtles have a very tight, smooth and streamlined look, usually lacking the heavy epibiont load (e.g., barnacles and other organisms that live on their shell) found on other large marine animals.  They can also be readily identified from other species of sea turtles based on the counts of the scutes on the carapace (large scales that make up dorsal portion of a turtle’s shell).  Turtle carapaces have three rows of scutes running down the back of the turtle from head to tail; the two outside rows of scutes (known as the costal scutes) will have a count of four, while the middle row known as the vertebral will have five scutes.  Additionally, hatchling green turtles display a distinct countershading, dark gray almost blue on top while pure white below, whereas juveniles, subadults and adults have splotches of brown, green, yellow, and black on their carapaces, that come in a wide variety of patterns.

Distribution and habitat

 Adrienne McCracken/ Loggerhead Marinelife Center

Adrienne McCracken/ Loggerhead Marinelife Center

Green turtles are found throughout Florida’s marine waters on both coasts.  Each of the life stages can be found in differing habitats throughout Florida.  Nests that are laid on Florida’s beaches hatch after about two months of incubation.  Hatchlings then make their way to the water, where they rely on wave and magnetic orientation to take them out to the offshore pelagic zones of the Gulf of Mexico and the Atlantic Ocean.  Here, these turtles encounter weedlines and mats of Sargassum and other floating debris.  These hatchlings take refuge in these mats and feed on a variety of small invertebrates and other animals associated with the habitats.  Once they begin to reach a juvenile size, green turtles then move towards the nearshore Florida waters and undergo a dietary shift from an opportunistic carnivore to a nearly pure herbivore.  Juvenile green turtles can be found on relatively shallow nearshore grass flats, rocks, reefs, and jetties where they graze on a variety of algae and seagrasses.  As they approach adult size, green turtles leave these shallow nearshore waters for deeper seagrass pastures, including those in more tropical locations.  Once mature, both male and female turtles will return to regions from which they were hatched and congregate to mate.  Adult females will deposit up to seven clutches of eggs over a three-month period with each clutch containing between 100-150 eggs. 

While Florida and its waters host all four life stages, green turtles do not necessarily spend their entire lives in Florida waters.  Green turtles are long lived and highly migratory.  Hatchlings can ride ocean currents throughout the Gulf of Mexico, and through the Atlantic to Bermuda and even the coast of Africa.  Juvenile, subadult and adult foraging grounds of turtles hatched in Florida may occur from the Florida Keys, Texas, and throughout the Caribbean, particularly in the Bahamas, Cuba, and Mexico.  This large-scale movement occurs from turtles originating elsewhere; recent mark-recapture efforts and genetic studies have found juveniles, subadults and adults foraging in Florida waters originating from nesting beaches beyond Florida, including countries such as Brazil, Costa Rica, Nicaragua, Panama, and Mexico.   

Threats

 Inwater Research Group

Inwater Research Group

Green turtles face a number of anthropogenic threats throughout their lives.  Nesting beaches are threatened with habitat loss through development, shoreline hardening, and sea level rise.  Ocean-going turtles are subject to being incidentally injured and/or killed in commercial fisheries and legalized hunting for the species still exists in some countries throughout the world.  Marine pollution in the forms of plastic debris can choke animals when mistaken as jellyfish and consumed.  This debris also converges in the same weedlines utilized by hatchlings, who eat bits of degraded plastic, where it can compact in their intestines.  Discarded fishing nets, known as “ghost nets” float through the ocean silently, entangling and drowning animals getting tangled within.  Oil spills can also cause greatly harm green turtles as well; the National Oceanic and Atmospheric Administration estimated that upwards of 200,000 sea turtles were impacted that by the 2010 Deepwater Horizon Oil Spill in the Gulf of Mexico.

Population Status

Populations numbers of green turtles are tracked using the number of nests laid on Florida’s beaches each year.  When surveys began in the 1980’s only 10-12 nests were found in a single year.  However, nesting numbers have been rapidly increasing since then, with over 25,000 being laid in 2015.  While considered “endangered” by the International Union for Conservation of Nature (IUCN), this rapid growth has prompted the population of green turtles in the northwest Atlantic to be considered “threatened” by the Endangered Species Act.  Through the hard work of thousands of people in both the private and public sectors, this species appears to be on track for a conservation success story, although continued efforts are still required to ensure this species success.

Links for more information

http://inwater.org/projects/projects-overview/

 https://biology.cos.ucf.edu/marineturtleresearchgroup/

http://myfwc.com/research/wildlife/sea-turtles/nesting/green-turtle/

https://books.google.com/books/about/Our_Sea_Turtles.html?id=DKrpoQEACAAJ

https://www.facebook.com/InwaterResearch