X. Longevity and Causes of Death.
Scientists are still researching sea turtle longevity. Once sea turtles reach sexual maturity, they may have an estimated reproductive life of about 30 years. Given that some species reach maturity at 50 years, an 80-year lifespan is feasible.
Currently there is not an adequate method of aging sea turtles. The most accepted method, aside from observing a turtle from the time it hatches, is to study growth rings of the scales on the carapace and plastron. Scientists count the rings and use a mathematical formula to estimate a turtle's age.
C. Natural predators.
1. Adult sea turtles have few predators, mostly large sharks. Tiger sharks, in particular, are known for eating sea turtles. Killer whales have been known to prey on leatherback turtles.
2. Fishes, dogs, seabirds, raccoons, ghost crabs, and other predators prey on eggs and hatchlings. Most than 90% of hatchlings are eaten by these predators.
3. Flatback turtle nests are susceptible to predation by monitor lizards, dingoes, and introduced foxes.
Green sea turtles are black sea turtles may develop lobed tumorlike growths (fiborpapillomas) on the skin. These growths can result in reduced vision, obstruction of normal swimming and feeding, and increased susceptibility to secondary parasitism and infection.
E. Human impact.
1. Nesting areas are becoming scarce due to beach development and disturbances. Kemp's ridleys only nest on one beach in the entire world: on a remote beach in Mexico near the village of Rancho Nuevo (about 161 km, or 100 miles, south of the Texas border). In 1947, scientists witnessed an arribada of more than 40,000 Kemp's ridley turtles in one day. In the 1960s, numbers were reduced to less than 5,000 turtles. In 1973, the largest arribada contained only 200 individuals.
2. Although the population of olive ridley sea turtles is the most abundant in the world, their major nesting beach at Gahirmatha in Orissa, India is in jeopardy. The Government of India is planning to develop a major fishing port and processing plant 10 km (6.2 miles) from the critical nesting beach. More sea turtles nest on this beach than on any other beach in the world.
3. Nesting females and hatchlings are disturbed by the presence of trash on nesting beaches. If trash impedes its crawl up the beach, a female returns to the sea instead of nesting.
4. The noise and activity of people on the beach also may cause females to return to the sea instead of nesting.
5. Some sea turtles die when they ingest trash. Leatherbacks are especially susceptible to ingesting plastic, mistaking it for jellyfish.
6. Thousands of sea turtles drown in shrimp nets each year. Sea turtles forage in waters where commercial shrimpers trawl. In 1947, 5,000 U.S. shrimping trawlers worked in the Gulf of Mexico. That number increased to 15,000 full-time and 40,000 part-time trawlers by 1989.
7. Artificial lighting on beaches may misrepresent the time of day to turtles attempting to nest. Most turtles are noctural nesters, and to a turtle that has not yet come ashore to nest, a brightly lighted beach may signify daylight and inhibit nesting.
8. Hatchlings can become disoriented by city and street lights when trying to find the surf. Many young turtles actually head away from the ocean and toward parking lots. These animals may be eaten by predators or crushed by cars. Some die from exposure.
9. Some people illegally collect turtle eggs for food and for their alleged aphrodisiac effect.
10. Sea turtles are hunted (illegally in this country and in some cases legally elsewhere) for their meat and shells, which are used to make combs, eyeglass frames, aphrodisiacs, and curious. The fat of green sea turtles, boiled with cartilage called calipee, made a popular soup, which led to the decline in green sea turtle population numbers.
11. Deforestation may indirectly threaten sea turtle nests. Costa Rica has one of the highest deforestation rates in the world. Some researchers fear that without the forest to draw up ground water, the water table will rise beneath the beaches and drown nests.
12. Propeller and collision injuries from boats are not uncommon. These types of injuries are more frequent in areas with a high level of recreational boating, such as South Florida, the Florida Keys, and the United States Virgin Islands.
©2002 Busch Entertainment Corporation.