Loggerhead Sea Turtle

Caretta caretta

Description

Adult and subadult loggerhead sea turtles have a reddish-brown carapace. The dorsal and lateral head scales and the dorsal scales of the extremities are also reddish-brown, but with light yellow margins that vary enough in extent to provide considerable disparity in appearance among individuals. The unscaled area of the neck, shoulders, and limb bases are dull brown above and medium yellow laterally and ventrally. The plastron is also medium yellow. The thick, bony carapace is covered by nonimbricated horny scutes. Carapace length of adult southeastern U. S. loggerheads is about 36 in (92 cm) and body weight about 250 lb (113 kg). Elsewhere adult loggerheads are somewhat smaller, the most notable being those in Colombia, Greece, and Tongaland. Loggerheads rarely exceed 48 in (122 cm) in length or 500 lb (227 kg) in weight.

Hatchling loggerhead turtles lack the reddish tinge of adults and vary from light to dark brown dorsally. Both pairs of appendages are dark brown above and have distinct white margins. The plastron and other ventral surfaces may be described as dull yellowish-tan and there is usually some brown pigmentation in the phalangeal portion of the web ventrally. Hatchlings have three dorsal keels and two plastral ones.

The loggerhead turtle can be distinguished from other sea turtles by two pairs of prefrontal scutes, an extremely large head, the nuchal scute touching the first costal scute, three pairs of enlarged infra-marginal scutes, two claws on each flipper, and the heart-shaped and depressed carapace.

The crawls of nesting female sea turtles are distinctive interspecifically. Female loggerhead sea turtles leave a moderately deep cut track with alternating, asymmetrical diagonal marks made by the front flippers. The nest itself is a smaller mound of sand than those formed by the Atlantic green and leatherback sea turtles. The body pit depression is also considered insignificant relative to that of the Atlantic green and leatherback sea turtles.

Behavior

It has been assumed that male loggerheads migrate with females from distant foraging areas to the waters off nesting beaches and that courtship and mating take place there. The few reports concerning the seasonality of mating clearly place it in a period from late March to early June. While a few adult males may remain off the Florida coast throughout the year, most of them apparently depart by about mid-June, leaving the females to ascend the nesting beaches and deposit clutches throughout the summer. Nevertheless, courtship and mating are not well studied in loggerheads and there is no doubt that this and virtually every other aspect of the biology of male loggerheads needs further research and clarification.

In the southeastern United States, adult female loggerheads begin to nest as early as mid-March and they continue to do so until late September. Nesting activity is greatest in June and July. In Georgia, South Carolina, and North Carolina the season generally begins in mid-May and ends by mid-August. Loggerheads are known to nest one to seven times within a nesting season; the mean is approximately four times. The internesting interval varies around a mean of about 14 days. Female loggerhead sea turtles mate prior to the nesting season and then lay multiple clutches of fertile eggs throughout some portion of the nesting season. Along the southeastern U. S. coast, mean clutch size is about 100-126 eggs.

Loggerheads are nocturnal nesters, but they will infrequently nest during the day. Multi-annual remigration intervals of two and three years are most common in loggerheads, but the number can vary from one to six years. Natural incubation periods for U. S. loggerheads average from 53-55 days in Florida to 63-68 days in Georgia and North Carolina. The length of the incubation period is inversely related to nest temperature. Sex determination in loggerhead hatchings is temperature dependent and the species apparently lacks sex chromosomes. Natural hatching success rates of 73.4% and 55.7% have been reported in South Carolina and Florida, respectively.

Adult loggerheads become migratory for the purpose of breeding. Recoveries of females tagged while nesting on the Florida east coast suggest widely dispersed foraging in the Gulf of Mexico, Cuba and elsewhere in the Greater Antilles, and the Bahamas. While conclusive evidence is lacking as yet, it is assumed that these females remigrate hundreds or thousands of miles at multi-annual intervals to nest on the good, high-energy nesting beaches of east Florida. Migratory paths have been documented from Georgia to Cape Hatteras, North Carolina, and a single recovery of a Georgia-tagged female on the Florida Gulf Coast was reported. Little else is known of the travels of loggerhead sea turtles that nest in Georgia, South Carolina, and North Carolina outside of the nesting season.

Loggerhead hatchlings engage in a swimming frenzy for about 20 hours after they enter the sea and that frenzy takes them about 14-17 mi (22-28 km) offshore. At some point thereafter they become associated with sargassum rafts and/or debris. Upon reaching about 18 in (45 cm) in length, they abandon their pelagic existence and migrate to nearshore and estuarine waters of the eastern United States, the Gulf of Mexico, and the Bahamas and begin the subadult stage. Little is known of their seasonal movements there, but subadults of the Port Canaveral aggregation disperse more widely in the spring and early summer.

While the list of food items eaten by loggerheads is lengthy and includes invertebrates from eight phyla, it is clear that subadult and adult loggerheads are, first and foremost, predators of benthic invertebrates such as gastropod and pelecypod mollusks and decapod crustaceans. Coelenterates and cephalopod mollusks are also taken by larger turtles but these invertebrates are especially favored by logger-heads in the pelagic stage. Most of the evidence for the latter statement comes from the island groups of the eastern Atlantic. Post-hatchling loggerheads evidently ingest macroplankton. Loggerheads may scavenge fish or fish parts or ingest fish incidentally in some circumstances, but they are not fish eaters.

Habitat

Habitat selection for loggerhead sea turtles is not well understood, but it seems clear that adults can utilize a variety of habitats. Remote recoveries of female loggerhead sea turtles tagged in Florida indicate that many migrate to the Gulf of Mexico, often to the turbid, detritus-laden, muddy-bottom bays and bayous of the northern Gulf Coast. Still others apparently occupy the clear waters of the Bahamas and Antilles, where the sandy bottoms, reefs, and shoals constitute a totally different type of habitat. Nothing is known of the relative periods of time that loggerhead sea turtles may spend in these disparate habitats or of their propensity to move from one to another.

In most nearshore waters in the southeastern United States, adult and subadult loggerhead sea turtles appear to use the same habitats. In some of the inshore waters such as the Indian River Lagoon of east Florida the subadults are virtually isolated from the adults, whose foraging areas outside of the nesting season are apparently in the Bahamas, the Antilles, or the Gulf of Mexico.

As a generality, adult female loggerheads select high-energy beaches on barrier strands adjacent to continental land masses for nesting. There is some evidence that loggerhead sea turtles favor steeply sloped beaches with gradually sloped offshore approaches. After leaving the beach, hatchlings apparently swim directly offshore and eventually become associated with sargassum and/or debris in pelagic drift lines that result from current convergences. The evidence suggests that when post-hatchlings become a part of the sargassum raft community they remain there as juveniles, riding oceanic surface currents for several years. At that point they abandon the pelagic habitat, migrate to the nearshore and estuarine waters along continental margins, and utilize those areas as the developmental habitat for the subadult stage.

Distribution

The geographic distribution of loggerhead sea turtles includes the temperate and tropical waters of both hemispheres. The species inhabits the continental shelves and estuarine environments along the margins of the Atlantic, Pacific, and Indian Oceans. In the Western Hemisphere it ranges as far north as Newfoundland and as far south as Argentina and Chile. The nesting range is confined to lower latitudes, but loggerhead nesting is clearly concentrated in the north and south temperate zones and subtropics, with an aversion exhibited to beaches in Central America, in northern South America, and throughout the Old World Tropics. Notable exceptions to this rule would include the largest known nesting aggregation, on Masirah and the Kuria Muria Islands of Oman in the Arabian Sea and perhaps the nesting assemblage on the Caribbean coast of Quintana Roo, Mexico, which was reported in the late 1990s. Worldwide, 88% of loggerhead sea turtle nesting occurs in the southeastern United States, Oman, and Australia.

Loggerhead sea turtles nest along the coast within the continental United States from Louisiana to Virginia. Major nesting concentrations are found on the coastal islands of North Carolina, South Carolina, and Georgia, and on the Atlantic and Gulf coasts of Florida. Although they nest in all coastal counties in south Florida, the majority of nesting occurs along the east coast of Florida, particularly in Brevard, Indian River, St. Lucie, Martin, Palm Beach, and Broward Counties. In 1984, 14,150 females nesting per year was estimated for the southeastern United States; in 1989 the estimate was 58,000. Based on more extensive ground and aerial surveys throughout the Southeast since 1990, an estimated 60,000-70,000 nests are deposited annually. The numbers of turtles nesting fluctuates substantially from one year to the next, however, making interpretation of beach counts difficult. These totals are believed to constitute about 35-40% of the loggerhead nesting known worldwide. About 80% of loggerhead nesting in the southeastern United States occurs in six Florida counties: Brevard, Indian River, St. Lucie, Martin, Palm Beach, and Broward.

Throughout Florida, loggerhead sea turtle nests account for the vast majority of reported nesting; they comprised 97.9% of the total nesting activity during 1979-92. During 1988-92, while survey efforts remained relatively constant, the total number of reported loggerhead nests statewide fluctuated between 37,242 and 68,614. Between 1989 and 1995, nesting numbers fluctuated between 39,172 and 59,379.

Threats

A variety of natural and introduced predators such as raccoons, feral hogs, armadillos, opossums, foxes, ghost crabs, and ants prey on incubating eggs and hatchling sea turtles. The principal predator of loggerhead sea turtle eggs is the raccoon, which is particularly destructive and may take up to 96% of all eggs laid in nests deposited on a beach. In 1996, Hobe Sound National Wildlife Refuge (located north of West Palm Beach in Martin County) experienced depredation in 23% of the nests enumerated. In addition to the destruction of eggs, some of these predators may take considerable numbers of hatchlings just prior to or upon emergence from the sand.

Predation of hatchling and very young turtles is assumed to be significant. Hatchlings entering the surf zone and pelagic-stage hatchlings may be preyed upon by a wide variety of fish species and to a lesser extent, marine birds. Predators of juvenile and adult turtles include at least six species of sharks, killer whales, bass, and grouper. Tiger sharks appear to be the principal predator of subadult and adult turtles.

Conservation and Recovery

The loggerhead turtle is listed as a threatened species throughout its range by the U. S. Fish and Wildlife Service. In addition, it is considered endangered by the IUCN and international trade in its body parts is prohibited by CITES. Recent data suggest that the nesting populations in South Carolina and Georgia may be declining, while those in Florida appear to be stable. Globally, the species continues to suffer an overall decline. The conservation and recovery of the loggerhead turtle requires that its nesting beaches be protected from development and other causes of degradation, that the nesting females not be killed as a source of meat or their eggs collected as food, and that turtles not be hunted at sea or caught in large numbers as fishery by-catch (especially in trawls used to catch shrimp). In the United States, it is illegal to kill nesting loggerheads or take their eggs, and this is also true of most other countries where the species nests. However, egg poaching and killing of adults still occur in some areas (even in the United States). In addition, many of the U.S. nesting beaches are not being conserved in ways that protect the nesting habitat of these sea turtles. It is crucial that more attention be paid to the strict protection of key nesting beaches within parks or ecological reserves, and that erosion and other damages caused by off-site beach-front development be controlled. Damages caused by the recreational use of many beaches by pedestrians and off-road vehicles must also be dealt with more effectively than at present. Nearby artificial lighting must also be controlled, as it causes the misorientation of both adults and hatchlings (they are attracted to the lights, and may then move inland when leaving the nest instead of towards the ocean, often resulting in death of the turtles). It is also crucial that turtle excluder devices (or TEDs) be further refined and extensively used in the shrimp fishery, to prevent the lethal by-catch of loggerheads and other species of sea turtles. Ways of preventing by-catch in other fisheries, such as those using gillnets and long-lines, must also be developed and implemented. Other threats requiring control include the invasion of nesting beaches by non-native vegetation, the dredging of inshore marine habitats used by the turtles, and pollution by plastics and other debris. The depleted populations of the loggerhead turtle will not recover unless these various measures are vigorously implemented within the United States and other countries in the global range of this species.

Contacts

National Marine Fisheries Service
Office of Protected Resources
1315 East-West Highway
Silver Spring, Maryland 20910
Fax: (301) 713-0376
http://www.nmfs.gov/prot_res/prot_res.html

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103-1306
Telephone: (505) 248-6911
Fax: (505) 248-6915
http://southwest.fws.gov/

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

Carr, A. F., L. Ogren, and C. McVea. 1980. "Apparent Hibernation by the Atlantic Loggerhead Turtle Caretta caretta off Cape Canaveral, Florida." Biological Conservation 19: 7-14.

Davis, G. E., and M. C. Whiting. 1977. "Loggerhead Sea Turtle Nesting in Everglades National Park, Florida, U.S.A." Herpetologica 33: 18-28.

Talbert, D. R., et al. 1980. "Nesting Activity of the Loggerhead Turtle (Caretta caretta ) in South Carolina." Copeia 4: 709-718.

U. S. Fish and Wildlife Service. 1984. "Recovery Plan for Marine Turtles." U. S. Fish and Wildlife Service, Atlanta.

U. S. Fish and Wildlife Service. 1991. "Recovery Plan for the U.S. Population of Loggerhead Turtle." U. S. Fish and Wildlife Service, Atlanta.