Galápagos Green Sea Turtles
There are 7 extant (still living today) sea turtles that occupy the tropical and warmer temperate oceans of the world. Sea turtles share the characteristic of a bony shell, which is a specialized skeletal feature that is composed of such bones as the vertebrae, ribs, sternum and clavicles (collar bones), with their freshwater and terrestrial relatives. Sea turtles are unique among chelonians in that they have front limbs that are modified as flippers that propel them through the water by both upward and downward strokes. Sea turtles also have specialized glands near their eyes that help to rid them of excess salt that they absorb from the surrounding marine waters. Not only are sea turtles interesting in their own rite, most are critically endangered due to overharvesting, by-catch in fishing trawls, or loss of suitable marine and terrestrial nesting habitats.
Sea Turtles are almost entirely aquatic throughout most of their lives, venturing onto land only for laying eggs or for basking is a few populations. Some sea turtle species take up residence in an area such as a stretch of coastline, and remain there for their entire lives. Others, however, may establish foraging (feeding) grounds in one part of the world and travel to a nesting beach in another part of the world for egg laying (some migrate over 2000 km/1300 miles)(http://www.conserveturtles.org/seaturtleinformation.php?page=behavior). Nesting beaches can be “natal beaches” where an adult, nesting female hatched from an egg several decades earlier! After 60-80 days or more, hatchling turtles emerge from the sand altogether and dash to the sea, swimming until they find suitable habitat in floating, oceanic (open ocean) marine vegetation. After a few years, juvenile sea turtles return to the coast where they set up residence.
The Green Sea Turtle
Perhaps the most abundant sea turtle in the world is the Green Sea Turtle, or better known to scientists as Chelonia mydas. The species gets its common name from its green-colored fat found largely under its carapace (the top of the shell). In addition to Green Sea Turtles, there are currently 6 other recognized species. Most species are similar to, and closely related to, the Green Sea Turtle and they include the Loggerhead Sea Turtles, Atlantic and Pacific Ridley Sea Turtles, the Hawksbill Sea Turtle, and the Flatback Sea Turtle. The oddball is the more distantly related Leatherback Sea Turtle that possesses small scales as opposed to scutes (large shield-like scales) and that tends to live in the open ocean where it feeds on jellyfish.
Green Sea Turtles exist around the world in tropical and warmer temperate waters. However, different breeding populations of Green Turtles exist around the globe with only occasional intermixing of turtles. Generally, the cold waters of the extreme north and south Atlantic and Pacific Oceans act as barriers to the mixing of Atlantic and Pacific populations of Green Sea Turtles. Most mixing of populations, however, appears to be related to the movements of males among breeding groups (subpopulations). Atlantic populations include the Caribbean/Western Atlantic, Eastern Atlantic/West African and Mediterranean.
The Pacific Population is of most interest to us here and exists as the Western Pacific (including Hawaii) and Eastern Pacific (including turtles in coastal North, Central and South American waters, including the Galápagos). Eastern Pacific Green Turtles tend to be slate black, often highly flecked with relatively small dark markings while the Western Pacific Green Sea Turtles tend to be a lighter brown to dark yellow color and usually heavily streaked.
Around the Galápagos Islands, most Green Sea Turtles are the typical Eastern Pacific black form, or what we call a “black morph.” Occasionally, however, a Western Pacific “yellow morph” is encountered among the black morphs suggesting that some Galápagos Green Sea Turtles are migrants from somewhere in the Western Pacific. The obvious question to ask, then, is:
From Where Does the Western Pacific Yellow Morph Green Sea Turtles Come?
To answer that question, Professors John Rowe and David Clark of Alma College and Juan Pablo Munoz and Danielle Alcarone of the Galápagos Science Center have joined forces to solve the mystery of the “yellow morph” Green Sea Turtles in the Galápagos. During 2015 and 2016, the DOW Digital Science Center and the Galápagos Science Center funded the use of GPS Satellite Tracking devices to study the movements of male yellow morph sea turtles. We focused on the movements of male sea turtles because: 1) male sea turtles are rarely tagged with GPS units and 2) males are responsible for integrating themselves among different breeding groups.
Above: GPS Tag on Back of Turtle
Above: “Black morph” and “Yellow morph” green sea turtles with tags.
Above: Alma College and Galapagos Science Center Green Sea Turtle Team.