II. Habitat and Distribution.
Sea turtles are found in warm and temperate seas throughout the world.
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.
1. 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.
a. 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
b. Black sea turtles migrate along the coast from breeding areas to feeding grounds between the northern and southern extremes of their distribution range.
c. Loggerheads leave foraging areas and travel on breeding migrations that range from a
few to thousands of kilometers (1 kilometer = 0.62 miles).
d. 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
e. Populations of olive ridleys have been observed in large flotillas traveling between
feeding and nesting grounds in the Eastern Pacific and Indian Oceans.
f. 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.
g. 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).
h. 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.
2. 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.
3. Recently radio, sonic, and satellite tracking have been successful in monitoring sea turtle movements.
4. 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.
1. Total population figures are often unknown because juvenile and male sea turtles do not come ashore and are difficult to count.
2. 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.
3. 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.
a. 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.
b. 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.
c. 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.
d. 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.
e. 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.
f. 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.
g. 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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