The total population is often unknown because juvenile turtles and male turtles do not reach land and are difficult to count.
Population data is usually based on the number of adult females that come ashore to nest. However, this number is ambiguous—some females nest every two to three years, some may nest more than once on the same beach in a single season, and some females will visit more than one nesting beach in a season. Researchers rely more on changes in the number of nesting females from year to year to determine population trends of increase or decrease. Since short-term fluctuations from year to year related to the number of nesting females can be misleading, even surveys lasting one decade or less may not be sufficient to determine population trends.
So, based on records, the following has been found:
- Kemp’s Ridley Turtle is the most endangered sea turtle. In 1947, it was estimated that there were at least 92,000 nests. The number has dramatically decreased since then. Surveys conducted between 1978 and 1988 showed an average of only about 800 nests per year. Since 1978, the trend has shown that the number of nests has decreased by about 14 nests per year. The total number of nesting females may be as low as 350 on the beaches where tens of thousands of Kemp’s ridley turtles once nested.
- Green and Hawksbill Turtles populations have not been surveyed long enough to determine trends. However, qualitative observations of female turtle visits over the years indicate a significant decline.
Eastern Pacific Black Turtle
- Loggerhead Turtle‘s main nesting areas are located in the southeastern U.S. Population trends of loggerhead turtles show a decline in nesting areas in Georgia and South Carolina, but no decrease or potential increase has been observed in the southern Florida Atlantic region. Years of research on nesting behavior data and population biology studies are needed to assess trends in Florida.
- Olive Ridley Turtle populations can reach several hundred thousand adult females. The olive ridley is the most abundant sea turtle in the world. In 1991, it was estimated that 610,000 turtles nested within a week on beaches in India.
- Very little data is available on the population of the hawksbill turtle. Estimating the population size of nesting females is difficult through aerial observations: tracks in the sand do not last long and are hard to see, and nests are often obscured by beach vegetation.
- The population of flatback turtles is currently unknown; however, due to their limited distribution, flatbacks are the most vulnerable of all sea turtles to habitat changes or overexploitation.
There may be fewer than 115,000 leatherback turtles worldwide. There are too few records to predict trends; however, the numbers do not seem to be declining.
