Sea turtle populations have dramatically declined in numbers over the past half century. Green sea turtles (Chelonia mydas ), hawksbills (Eretmochelys imbricata ), Kemp's Ridleys (Lepidochelys kempii ), loggerheads (Caretta caretta ), and leatherbacks (Dermochelys coriacea ) have all had their numbers decimated by human activity. The decline has been caused by several factors, including the development of a highly industrialized fishery to meet the demand for seafood on a worldwide basis. The most economical fishing method involves pulling multiple nets underwater for extended periods of time, and any air-breathing animals, such as sea turtles, which get caught in the net are usually drowned before they are hoisted on board.
In the United States, this problem has led to the introduction of the turtle excluder device (TED), which must be placed on each tow net used by commercial shrimpers and fishermen. These cage-like devices have a slanted section of bars which allow fish and shellfish into the net but deflect turtles. These highly controversial devices have been mandatory for less than a decade, but there are some indications that they are saving thousands of turtles per year.
As significant as the impact of commercial fishing may seem, it does little to sea turtle populations compared to losses incurred at the earliest stages of the turtles' life history. In the late 1940s, along an isolated beach near Tamaulipas, Mexico, an extremely dense assemblage of sea turtles were observed digging out nests and laying eggs at the beach. So many females were present that they were seen crawling over one another and digging out the nests of others in order to lay their own eggs. At this location alone, the sea turtle population was estimated in the millions. In the early 1960s, scientists realized that the turtles found at Tamaulipas were a distinct species , Kemp's Ridley, and that they nested nowhere else in the world; but by that time the population had declined to only a few hundred turtles.
Threats to the survival of newly hatched sea turtles have always been enormous; crows, gulls, and other predators attack them as they scurry seaward, and they are prey for waiting barracudas and jacks as they reach water. Other animals raid their nests for the eggs, and humans are among these nest predators, collecting the eggs for food. Sea turtles concentrate their numbers in small nesting locations such as Tamaulipas in order to greatly outnumber their natural predators, thus allowing for the survival of at least a few individuals to perpetuate the species. However, this congregating behavior has contributed to their demise, because it has made human predation easier and more profitable.
Adult turtles are harvested as a protein source in many Third World countries, and many turtles are also subjected to increasing levels of marine pollution . Both of these factors have contributed to the sharp decline in their population. Public awareness and conservation efforts may keep sea turtles from extinction , but it is not clear whether species will be capable of rebounding from the decimation that has already taken place.
[Eugene C. Beckham ]
Bjorndal, K. A., ed. Biology and Conservation of Sea Turtles. Washington, D.C.: Smithsonian Institution Press, 1981.
Carr, Archie. So Excellent a Fish: Tales of Sea Turtles. New York: Scribners, 1984.
National Research Council. Decline of the Sea Turtles: Causes and Prevention. Washington, DC: National Academy Press, 1990.
Ezell, C. "Turtle Recovery Could Take Many Decades." Science News 142 (August 22, 1992): 118.
"Sea Turtle Nesting Begins Soon." The Florida Times Union (April 13, 2002): L–13.
Stolzenburg, W. "Requiem for the Ancient Mariner." Sea Frontiers 39 (March–April 1993): 16–18.
National Marine Fisheries Service. [cited May 2002]. <http://www.nmfs.noaa.gov>.