Distribution

Sea turtles are found in warm and temperate seas throughout the world.


Habitat

Adults of most species are found in shallow, coastal waters, bays, lagoons, and estuaries. Some also venture into the open sea. Juveniles of some species may be found in bays and estuaries, as well as at sea.

Migration

Migration habits differ not only among species but also among different populations of the same species. Some sea turtle populations nest and feed in the same general areas; others migrate great distances.

Green sea turtle populations migrate primarily along the coasts from nesting to feeding grounds. However, some populations will travel 2,094 km (1,300 miles) across the Atlantic Ocean from the Ascension Island nesting grounds to the Brazilian coast feeding grounds.

Black sea turtles migrate along the coast from breeding areas to feeding grounds between the northern and southern extremes of their distribution range.

Loggerheads leave foraging areas and travel on breeding migrations that range from a few to thousands of kilometers (1 kilometer = 0.62 miles).

Kemp's ridley turtles follow two major routes in the Gulf of Mexico: one northward to the Mississippi area, the other southward to the Campeche Bank, near the Yucatan Peninsula.


Populations of olive ridleys have been observed in large flotillas traveling between feeding and nesting grounds in the Eastern Pacific and Indian Oceans.


Hawksbill migration studies have been limited. Evidence suggests that some hawksbill populations show cyclic nesting migrations. Other researchers have documented nonmigratory and short-distance migratory populations.


Flatbacks move from their nesting grounds on the northern coast of Australia and islands to feeding grounds in shallow waters of northeastern Australia. Distance covered ranges from 215 to 1,300 km (134 - 807 miles).

Leatherbacks have the longest migration of all sea turtles. They have been found more than 4,831 km (3,000 miles) from their nesting beaches.




Migration habits differ among sea turtle species. Migrations may range from a few to thousands of kilometers.


The most common method used to track free-ranging sea turtles is flipper tagging. Although this method yields information on migration destinations, it does not reveal travel routes.


Recently radio, sonic, and satellite tracking have been successful in monitoring sea turtle movements.


Hubbs-Sea World Research Institute has developed a radio transmitter harness for leatherback turtles. Its design allows secure attachment of a transmitter without affecting turtle mobility. The harness was designed to release within several months.



Population

Total population figures are often unknown because juvenile and male sea turtles do not come ashore and are difficult to count.

Population data are usually based on the numbers of adult females that come ashore to nest. Even then, the numbers are ambiguous - some females nest every two to three years, some may nest more than once on the same beach in a season, and some females will visit more than one nesting beach in a season.

Researchers rely more upon the changing numbers of nesting females from year to year to determine population trends of increasing or decreasing numbers. Because broad year-to-year fluctuations in numbers of nesting females make short-term data misleading, surveys of a decade or less may be insufficient to determine a population trend.


The Kemp's ridley is the most endangered sea turtle. In 1947, 92,000 nests were estimated. The numbers have been declining dramatically since then. Surveys conducted between 1978 and 1988 indicated an average of about 800 nests per year. Since 1978, the trend shows the number of nests have been declining at about 14 nests per year. The total number of nesting females may be as low as 350 on beaches where tens of thousands of Kemp's ridley used to nest.

Nesting populations of green and black sea turtles have not been surveyed long enough for determination of trends. However, qualitative observations during visits over several years suggest a heavy decline.


The major loggerhead nesting grounds are located in the southeastern U.S. Population trends of logger heads show a decline in nesting areas of Georgia and South Carolina, but no decline or a possible increase in southern Florida Atlantic areas. More years of nesting data and population biology studies are needed to assess the Florida trends.


There are probably several hundred thousand adult female olive ridleys. The olive ridley is the most abundant sea turtle in the world. In 1991, an estimated 610,000 turtles nested in a single week on a beach in India.


Very little data are available on hawksbill populations. Estimation of population sizes of nesting females is difficult by aerial assessment: tracks in the sand do not last long and are difficult to see, and nests are often obscured by beach vegetation.


Current population numbers for flatback turtles are not known; however, because of its restricted distribution, the flatback is the most vulnerable of all sea turtles to any habitat change or over-exploitation.

There are probably less than 115,000 adult female leatherbacks worldwide. There are too few records to predict trends; however, the numbers do not appear to be declining.

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Social Behavior

Sea turtles are not generally considered social animals; however, some species do congregate offshore. Sea turtles do gather together to mate. Members of some species travel together to nesting grounds. After hatchlings reach the water they generally remain solitary until they mate.

Individual Behavior

Little is known about the individual behavior of sea turtle species;

Green sea turtles are considered solitary, but occasionally from feeding aggregations in shallow waters abundant in seagrass or algae.

In the ocean, flatback turtles may spend hours at the surface floating, apparently asleep or basking in the sun. Frequently, seabirds perch on the backs of the flatbacks.

Hawksbill turtles spend some time resting or sleeping wedged into coral or rock ledges.

Olive ridleys have been observed basking on beaches, and it is not unusual to see thousands of olive ridleys floating in front of their nesting beaches.

Leatherback turtles tend to dive in a cycle that follows the daily rising and sinking of the dense layer of plankton and jellyfish. The turtles probably feed in the upper layers of water at night. As dawn approaches, their dives become deeper as the plankton and jellyfish retreat to deeper water, away form the light of day. The turtles bask at the surface at midday when the layer sinks beyond their typical diving range. As dusk approaches, the turtles' dives become more shallow as the layer rises.

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Food Preferences and Resources
Diet varies with species. Sea turtles may be carnivorous (meat eating), herbivorous (plant eating), or omnivorous (eating both meat and plants). The jaw structure of many species indicates their diet :

Green and black sea turtles have finely serrated jaws adapted for a vegetarian diet of sea grasses and algae. In adulthood, they are the only herbivorous sea turtles, but in an aquarium environment all sea turtle species can be maintained on a carnivorous diet.

Loggerheads' and ridleys' jaws are adapted for crushing and grinding. Their diet consists primarily of crabs, mollusks, shrimps, jellyfish, and vegetation.

A hawksbill has a narrow head with jaws meeting at an acute angle, adapted for getting food from crevices in coral reefs. They eat sponges, tunicates, shrimps, and squids.

Leatherbacks have delicate scissorlike jaws that would be damaged by anything other than their normal diet of jellyfish, tunicates, and other soft-bodied animals. The mouth cavity and throat are lined with papillae (spinelike projections) pointed backward to help them swallow soft foods.

Researchers continue to study the feeding habits of flatbacks. There is evidence that they are opportunistic feeders that eat seaweeds, cuttlefish, and sea cucumbers.


Eating Habits

Some species change eating habits as they age. For instance, green sea turtles are mainly carnivorous from hatchling until juvenile size; they then progressively shift to an herbivorous diet.

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