Life History: Loggerhead Life Cycle
Some sea turtles (leatherbacks, Greens, and Kemp's Ridleys) migrate annually through Georgia’s coastal waters and others (Loggerheads) nest on the sandy beaches of Georgia’s Golden Isles. Leatherbacks migrate northward each Spring following warming Atlantic waters and one of their favorite foods, jellyfish. Juvenile Kemps Ridleys regularly are found migrating through Georgia’s coastal waters, apparently waifs swept out of the Gulf of Mexico by the Gulf Stream. Two subpopulations of Loggerheads inhabit the Western North Atlantic, a robust Southern Subpopulation in middle and South Florida and a smaller, more endangered Northern Subpopulation in Georgia, The Carolinas, and Virginia.
Loggerheads, Georgia's common nesting turtle, spend their life in a drama involving hatching in Georgia's sandy beaches, scampering into the Atlantic in the dark of night, swimming in a frenzy for about three days to disperse to find Sargassum mats to colonize along oceanic convergence zones. The hatchlings then ride the oceanic currents as nektonic inhabitants of the floating algal mats feeding on smaller inhabitants as many are carried around the North Atlantic Gyre and spend time growing as juveniles in the Azores and perhaps in Mediterranean, before catching the North Equatorial current back to the Western North Atlantic. As late-stage juveniles and mature adults, Loggerheads migrate along the Eastern Seaboard's Inner Continental Shelf feeding and foraging for mollusks, crabs, fish, and other food items from Georges Banks to Florida.
During the nesting season, from early May until early August, some proportion of the Loggerhead female population migrates back to near the beaches from which they hatched, mate with several males by copulating either on the ocean's surface or perhaps beneath the surface. The males check female responsiveness by biting and nudging them, and when the female is receptive, climb onto the females carapace, holding on by hook-like clasping claws on their front flippers, wrap their long tails beneath the females shorter tail, and insert their cloacal-bound hemi -penises into the females cloaca to deposit their sperm. Females are impregnated by many males whose sperm fertilize the females eggs. Eggs are produced in the ovaries, fertilized, shelled with a flexible shell, and extruded through the oviducts to the cloacha, which becomes enlarged acting as the turtles oviduct during deposition of approximately four clutches of approximately 113 eggs, at about 10-14 intervals during the nesting season.
Loggerhead turtles nest on sandy temperate and/or tropical oceanic beaches, including those of St. Catherines Island following a sequence of hard-wired steps, called the Nesting Ethogram (Hailman and Elowson, 1992). After depositing eggs in an urn-shaped egg chamber, the female turtle immediately returns to the ocean; never seeing her young. The eggs hatch after about 60 days of incubation in the warm sand and the hatchlings dig their way to the surface. This process involves the turtles crawling over one another in a mass of wiggling little bodies. The turtles at the top bump the sandy ceiling of the egg chamber, knocking sand loose. The falling sand sifts through the mass of hatchlings and is trampled by them into the egg shells below. The process continues and the mass of hatchlings moves upward through the sand toward the surface. This process is called "stoping" and the air chamber containing the hatchlings is a "stope," both directly analogous to removing an ore body in an underground mine from the bottom to its top. As the hatchlings approach the surface, they become dormant if the sand is warm and continue stoping if it is cool; usually assuring emergence under the cover of darkness.
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| An underground air pocket called a "stope" is formed at hatching. As the turtle crawl over one another they knock sand loose above and trample it beneath themselves, moving the stope upward to the beach surface. | Stope chamber excavated in nest [95-045] after emergence during nor'easter in 1995, South Beach, St. catherines Island. Note screen maring original beach surface covered by buried wrack mat. |
When the babies emerge, normally in the dark of night, they scamper to the sea to avoid diurnal predators such as Raccoons, Feral Hogs, and Ghost Crabs. Their crawling direction is dictated by several cues, downhill slope, brighter sky over open ocean horizon, and, perhaps, the sound or sight of the surf. Even in the dark the hatchlings run a gauntlet of predators awaiting a tasty morsal!
After entering the ocean the hatchlings enter a swimming frenzy for about 24-72 hours, swimming perpendicular to wave fronts and dispersing widely through the ocean. Evidence now indicates that hatchling imprint on the Earth's magnetic field and use it for future navigation.
After entering the sea, we know very little about the life history of the baby turtles. We think Loggerheads live a pelagic existence for several years drifting with drift lines of Sargassum algae in oceanic currents. After approximately 20-30 years, the sea turtles reach maturity, breed, and the females search out sandy beaches upon which to nest and continue the life cycle. Some sea turtles are remarkable for nesting on the same beach time after time; perhaps the very beach upon which they were hatched. Other turtles show less fidelity to a single beach, but still tend to return to the same area to nest.
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| When hatchlings enter the sea, they begin to swim. They continue swimming for approximately 72 hours until they find floating Sargassum at convergence zones. | The presence of Sargassum in the Atlantic Ocean off the Georgia Coast is indicated by periodic "strandings" of Sargassum on the beaches of St. Catherines, as observed on 07/20/06 on North Beach. |
Sea turtles crawl onto the beach to find a nesting suitable place leaving behind diagnostic crawlways. If the turtle doesn’t nest, they leave a simple non-nesting crawlway; if they do nest, they leave not only a crawlway, but an elliptical disturbed area, the nest, in which they have deposited a clutch of eggs. It is thought that Loggerheads return to nest close to where they hatched, and once they successfully nest during a nesting season, evidence suggests they return multiple times to deposit clutches close to one another (called nesting fidelity).
Between nesting seasons, Georgia Loggerhead females take a break to rebuild their biologic resources, often migrating hundreds or thousands of kilometers with seasonal water temperature changes and/or following their preferred food source. These migration patterns can be viewed on many sites and these are accumulated on seaturtle.org.
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| A nesting Loggerhead, named Zapala, was fitted with a satellite tag by GaDNR on 05/30/2005 and released on Sapelo Island. She nested on St. Catherines island July 10, 2005. When Zapala finished nesting in 2005, she swam northward to Long Island. In 2006 Zapala swam back south, so it appeared that she was going to nest during 2006 in Georgia, but she didn't. Her migration route is shown on the map to the left (courtesy of Ga DNR and seaturtle.org). |
Each of the sea turtle species in each of its specific areas must necessarily have its own preferences for nesting areas, migration patterns, and foraging patterns. These patterns must have changed through time as currents, geography, and climates changed.
Leatherbacks nest in the tropics and, as fully oceanic animals, migrate great distances, even along the Georgia coast; living largely on jellyfish, often diving thousands of meters to find them. Hawksbills forage on sponges from reefs or rocky areas in clear, shallow water and nest on tropical beaches. Green Turtles are found around the world in tropical and subtropical oceans and occupy high-energy beaches, convergence zones in pelagic waters, and benthic feeding grounds in shallow waters where they often eat sea grasses or algae.
Loggerheads range through subtropical and temperate waters of the Atlantic, Pacific, and Indian Oceans, nesting on their sandy beaches, particularly of Oman and Florida (USA), but also in Georgia and South Carolina. Kemps Ridleys nest primarily at one beach in Mexico, Rancho Nuevo, and spend their adult life in the Gulf of Mexico except for some which are apparently carried into the Gulf Stream in the Atlantic Ocean.
The distribution, movement, and ecology of sea turtles remains a major research effort because we still know so little about them. Satellite tracking over the last few years has eliminated much of the mystery for adults, but we still have much to learn especially about the early part of the life cycles of sea turtles. Research now being done in many programs is rapidly defining the parameters of the early stages of the lifecycles of sea turtles, e.g. visit the Lohmann Lab.
Various aspects of the ecology of sea turtles make them susceptible to different hazards demanding different conservation mitigation during different parts of their life cycles. These hazards may be natural [i.e. storms, parasites, or predators] or may be anthropogenic [i.e. collisions with boats, drowning in gill nets or trawls, pollution, etc.]. Negative interactions that are natural [ie. non-human] have often been overcome during the evolutionary development of each species and are of little concern to sea turtle conservationists. Negative impacts that are due to unnatural [i.e. human] causes are not only new to sea turtles, but are increasingly severe, and tend to reinforce one another; driving these endangered turtle to the brink of extinction.