Various species of sea turtles are found in warm and temperate seas throughout the world. (See the table below for more information.)
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. (See table below for descriptions of each species' habitat.)
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 travel 2,094 km (1,300 miles) across the Atlantic Ocean; from Ascension Island nesting grounds (in the middle of the South Atlantic) to 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 can be a few thousand kilometers each way.
- Kemp's ridley turtles follow two major routes in the Gulf of Mexico: one northward to the Mississippi area, and 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. Researchers have documented nonmigratory and short-distance migratory populations.
- 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 its islands to feeding grounds in shallow waters of northeastern Australia. Distance covered ranges from 215 to 1,300 km (134 to 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.
Historically, scientists tracked a free-ranging sea turtle by tagging a flipper and documenting where the turtle was sighted. Although this method yields information on migration destinations, it does not reveal travel routes.
Most recently radio and satellite tracking have become more common in successfully monitoring sea turtle movements.
Hubbs-SeaWorld Research Institute has developed a radio/satellite 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.
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 because some females nest every two to three years; some may nest more than once on the same beach in a season; and some visit more than one nesting beach in a season.
Researchers rely on the changing numbers of nesting females from year to year to determine population trends. 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 species.
- In 1942, the nesting population at Rancho Nuevo, the only nesting area for the species, was estimated at about 42,000 Kemp’s ridleys. After rapidly declining to a low of less than 300 nesting females by 1986, the Kemp’s ridley population is now estimated at 5,000 adult females in the Gulf of Mexico.
- Nesting populations of green sea turtles have not been surveyed long enough to determine worldwide population numbers. Experts estimate that in the past 120 to 140 years green sea turtle numbers have declined by 48 to 67 percent.
- The largest green turtle nesting population is found at Tortuguero, on the coast of Costa Rica where about 22,500 green turtle females nest annually.
- Raine Island, on Australia’s Great Barrier Reef, has the second largest nesting population of about 18,000 females per season.
- Between 200 and 1,100 green sea turtles nest on beaches in the continental U.S.
- Hawksbill nesting population numbers are difficult to estimate. Hawksbill nests are often obscured by beach vegetation and their tracks do not last long in the sand. The largest hawksbill nesting population is in Australia’s Great Barrier Reef, where about 6,000 to 8,000 females nest each year.
- The major loggerhead nesting grounds are in Oman, Australia, and the southeastern U.S., particularly in southern Florida. Nearly all loggerhead nesting populations are declining. The worldwide population is unknown, although most populations outside of U.S. waters are declining.
- Only Florida and Oman have nesting loggerhead populations of greater than 10,000; with about 20,000 nesting females in Florida and 13,000 in Oman.
- In the U.S., total estimates for loggerhead nests per year range from 68,000 to 90,000.
- In the Pacific, about 1,200 loggerheads nest in Japan and eastern Australia.
- The olive ridley is the most abundant sea turtle in the world. Each year, there are probably about 500,000 to 600,000 females nesting in arribadas (mass nesting sites) in Costa Rica, 450,000 in Mexico and about 135,000 in India; with a total female population of about 2 million turtles. Yet, many of their populations are declining or have disappeared, mainly from egg poaching and accidental death in fishing gear.
Scientists estimate that 25,000 to 30,000 mature female flatbacks inhabit Australian waters. Because of its limited distribution, the flatback is the most vulnerable of all sea turtles to habitat change or exploitation.
Worldwide leatherback populations are not known. Most leatherbacks nest in the eastern Atlantic (at Gabon) and in the Western Atlantic (mainly French Guinea, Trinidad, and Suriname).
- Populations of more than 1,000 leatherback sea turtles nest in the Caribbean, Indian Ocean, and Western Pacific.
- In the United States, about 40 leatherbacks nest annually on beaches in Florida.
- Many of the nesting leatherback populations in the Pacific have declined by more than 80%.
- Trends are unclear for many other nesting populations, although they seem to be increasing at nesting beaches in the U.S. and at some Caribbean nesting sites.
Table: Sea Turtle Distribution & Habitat