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|Title:||Life history and environmental requirements of loggerhead sea turtles|
|Authors:||Environmental Impact Research Program (U.S.)|
Nelson, David A.
Sea turtle life history
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Technical report (U.S. Army Engineer Waterways Experiment Station) ; EL-86-2.|
Abstract: In the United States, scattered nestings of loggerhead sea turtles (Caretta caretta) may occur in most of its range from Texas to Florida and Florida to New Jersey; however, nesting concentrations occur on coastal islands of North Carolina, South Carolina, and Georgia and the coasts of Florida. The greatest portion of a loggerhead's life is spent in ocean and estuarine waters where they breed, feed, migrate, and hibernate. The remainder of their life is spent on coastal beaches where the female digs a nest and lays her eggs, the eggs hatch, and the hatchlings crawl to the water to become part of the aquatic system again. Mating is believed to occur in shallow water adjacent to nesting beaches just prior to nesting and egg laying. Nesting activity begins in the spring, peaks in midsummer, and declines until completion in late summer. A loggerhead female generally nests every other year or every third year. A small percentage nest at intervals less than 2 years or more than 3 years. When a loggerhead nests, it usually lays two to three clutches of eggs per season (range one to five). These interseasonal nestings are generally 12 to 14 days apart (range 11 to 20 days). Loggerheads may return to the same vicinity to nest between or within seasons, but they are not as site specific as green sea turtles (Chelonia mydas). Loggerhead eggs are similar in appearance to ping-pong balls, although slightly smaller and leathery, soft and pliable. The eggs hatch in 46 to 65 days (x = 60 days). Hatchling success/fertility rates in natural clutches are 80 to 90 percent. Hatch success and incubation time can be affected by clutch size, ambient sand temperature, sand compaction, and other physical parameters of the sand surrounding the nest. Hatchlings emerge from the nest as a group at night and orient seaward. The seaward orientation can be disrupted when lights from structures are directly visible from a nest. After reaching the water, hatchlings probably become pelagic. Juvenile loggerhead turtles utilize bays and estuaries for feeding. Adult loggerhead seem to prefer shallow coastal waters that are less than 60 m deep. Adults move north in summer and fall and move south when water temperatures decline in late fall and winter. Growth in sea turtles appears to be rapid from hatchling to young adult, becoming very slow at maturity. The rate of growth of sea turtles differs depending on quality and quantity of food. Although no longer commercially harvested in the United States, loggerheads are harvested in parts of the Caribbean for meat, skin, shell, and eggs. Loggerheads have died from fowling by, or ingestion of, petroleum and plastic products and from disease, chemical pollution, shark and killer whale predation, boat collisions, hypothermia, and accidental capture in shrimp and fish trawls. Sea turtle populations are difficult to census. The total number of mature females in the United States in 1983 was estimated to be between 28,000 and 73,000. It has been suggested that a group of 1,000 nesting females is expected to lay 300,000 eggs a season, from which 389 females must survive to maturity to replace the original 1,000 females. Loggerheads are primarily carnivorous. They eat a variety of benthic organisms including molluscs, crab, shrimp, jellyfish, sea urchins, sponges, squids, basket stars, and fishes. Eggs, hatchlings, juveniles, and adults are preyed upon by various animals. The most common predators of eggs and nests are raccoons, crabs, and hogs. Hatchlings are taken by mammals, birds, and crabs as they emerge from the nest and crawl to the water. The greatest predation is likely to be by nearshore fish after the hatchlings reach the water. Because of their size, predation on juvenile and adult sea turtles may be minimal; however, they have been taken by sharks, groupers, and killer whales. Temperature is a major factor influencing sea turtle life histories. Sand temperature affects nest site selection by adult females, the incubation time and hatching success of eggs, and the sex and emergence timing of hatchlings, whereas water temperature affects nesting activity and movements of adults. Loggerheads have the potential for accumulating contaminants through their primary food source, benthic invertebrates. Oil spills and tar balls can also affect loggerheads. Most management of sea turtles has been directed toward increasing hatching and hatchling success. Nest predation can be reduced by removal or elimination of the responsible animal. To prevent or reduce loss of nests and eggs to predators, erosion, or man's activities, nests may be relocated to safer spots on the beach or to hatcheries. Hatchlings may be raised in captivity until they reach a size believed to be less vulnerable to predation before they are released. This practice is referred to as head-starting.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Technical Report|
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