Loggerhead Sea Turtle
Caretta caretta

* Federal Threatened State Endangered *

Common Name:

Loggerhead Sea Turtle

Scientific Name:

Caretta caretta

Etymology:

Genus:

Caretta is derived from the French word caret  which means "a kind of turtle".

Species:

caretta is derived from the French word caret which means "a kind of turtle".

Average Length:

31 - 45 in. (79 - 114 cm), weight 170 - 350 lbs. (77 - 159 kg)

Virginia Record Length:

42.5 in. (108 cm)

Record length:

48+ in. (122+ cm), weight 500+ lbs. (227+ kg)

Systematics: Originally described as Testudo Caretta by Carolus Linnaeus in 1758 from literature citations, including Mark Catesby (1731-1743), dealing with the natural history of the American islands (Schmidt, 1953; Smith and Smith, 1979; Dodd, 1990). Linnaeus noted that this species was from the "insulas Americanas" but designated no type specimen. The type locality was restricted to the Bermuda Islands by Smith and Taylor (1950) and later to Bimini, British Bahamas, by Schmidt (1953). Rafinesque (1814) was the first to use the genus Caretta for this species but called it C. nasuta; Stejneger (1904) corrected the taxonomy. No subspecies are recognized (Iverson, 1992).

Description: A large sea turtle (Plate 15) reaching a maximum known carapace length (CL) of 213 cm (83.9 inches) and body mass of 450 kg (992 lb), but masses of up to 455 kg (1,000 lb) have been recorded (Ernst and Barbour, 1972, 1989a). In Virginia, straight-line CL was 43-108 cm (ave. = 67.0 ± 11.5, n = 255), plastron length (PL) was 31-78 cm (ave. = 50.5, n = 176), and body mass averaged 41.9 ± 19.1 kg (92.4 lb, n = 47) (Musicketal., 1985; Bellmund et al., 1987).

Morphology: Carapace heart-shaped without striations on the surface; middorsal keel present in young turtles and posterior margin serrated (less apparent in individuals >80 cm CL); marginal scutes 11-15 (usually 12) on each side, pleurals 5/5, and vertebrals 5; anteriormost vertebral scute rhomboidal in shape, and it and 1st pleural scute on each side contact the wide cervical (sometimes called nuchal) scute on leading edge of carapace; 2 longitudinal plastral ridges present on all but oldest adults; 3 (rarely 4) inframarginal scutes on bridge, which lack visible pores; 2 sets of prefrontal scutes (plates) anterior to a small frontal; head large (to 23 cm in width; 17-22% of CL) with a large, ovoid parietal scute.

Coloration and Pattern: Carapace mahogany to reddish brown, sometimes with a tinge of olive from the epibiota; hingeless plastron cream to yellowish and smaller than the carapace (71-75% of CL); star-shaped light and dark streaks may be present on carapace; dorsum of head, neck, and front of fore-flippers reddish brown; short snout and upper jaw yellowish brown; entire undersurface, side of the neck, and parts of flippers cream to yellow; fore-flippers large, about half the length of carapace; hind-flippers short and paddlelike. Each flipper bears 1 or 2 claws.

Sexual Dimorphism: Most of the loggerheads seen in Virginia waters are immature. Adult males have a narrow carapace and long tails that extend beyond the posterior margin of the carapace (Ernst and Barbour, 1989a).

Juveniles: Hatchling and juvenile loggerheads have a brown carapace with 3 dorsal keels on ver- tebrals 1-3; these project posteriorly. The tan to dark-brown plastron has 2 keels. Scutellation is as described for adults. Hatchlings from Virginia nests averaged 47 mm CL (42-53, n = 788) and weighed 13.9-28.1 g (ave. = 20.7, n = 788) (J. A. Keinath and J. A. Musick, pers. comm.).

Confusing Species: Kemp's ridleys (Lepidochelys kempii) are gray to olive green and white with 4 inframarginal scutes on the bridge with visible pores. The green turtle (Chelonia my das) has 2 pre- frontals, 1 triangular anteriormost vertebral scute, 4 pleural scutes, and the 1st pleural on each side is separated from the cervical scute by the 1st vertebral. The carapacial scutes on hawksbills (Eretmochelys imbricata) overlap posteriorly. Two other species are commonly found in brackish water: diamondback terrapins (Malaclemys terrapin) are gray with black markings and are under 22 cm CL; snapping turtles (Chelydra serpentina) are uniformly dark brown and have long tails with raised ridges. Both of these have 4-5 claws on each foot; sea turtles have 3 or fewer.

Geographic Variation: None in Virginia.

Biology: The Loggerhead Sea Turtle is completely marine; it is not found in freshwater. Research conducted by the Virginia Institute of Marine Science (VIMS) since 1979 has provided considerable information on the ecology of this species. The Chesapeake Bay is an important summer foraging area for subadults between the ages of 5 and 15 years (Lutcavage and Musick, 1985; Musick, 1988; Klinger and Musick, 1992). They are often seen in the channels and inlets of the barrier islands. Adults are more often seen in the Atlantic Ocean. Average CL of turtles in the Chesapeake Bay (66.7 ± 10.8 cm, n = 238) was significantly smaller than average CL of turtles found in coastal waters (72.3 ± 17.4, n = 46) (Bellmund et al" 1987). Over 80% of the C. caretta in Virginia's waters measured between 40 and 80 cm CL (Klinger and Musick, 1992). Loggerhead Sea Turtles enter the bay in May when the water temperature exceeds 18°C and leave by November when the temperature cools to 18°C (Keinath et al., 1987; Musick, 1988). Barco and Pitchford (1990) found four Loggerhead Sea Turtles stranded on Virginia beaches between 8 and 14 December 1989, apparently because of cold shock.

Loggerhead Sea Turtles forage in channels of the bay and estuaries, where they feed primarily on horseshoe crabs (Limulus polyphemus) (Lutcavage and Musick, 1985; Keinath and Musick, 1991a). Other prey occasionally taken are blue crabs (Callinectes sapidus), rock crabs (Cancer irroratus), spider crabs, clams, whelks, jellyfish, shrimp, fish (in pound nets), and seaweed (Lutcavage, 1981; Bellmund et al., 1987). The shells of these turtles are often encrusted with barnacles and other invertebrates, including worms and mollusks (Lutcavage, 1981). Sharks, especially tiger sharks (Galeocerdo cuvieri), are the primary predators of young Loggerhead Sea Turtles in coastal waters of Virginia (Lutcavage, 1981). Carr (1987) listed white-tip sharks (Carcharhinus longimanus) and dolphins as predators. Adults are killed by human-associated sources, such as drowning in fish nets and injury by boat propellers and gunshots. In many parts of their range, Loggerhead Sea Turtles and their eggs are eaten by local people. The highest source of mortality is by a variety of predators on eggs in nests. Predators and parasites were summarized in Dodd (1988).

There is no active nesting population in Virginia. One or two nests by single females are constructed on beaches each summer; the record number is six (Musick, 1988). Female age at maturity is estimated to be about 30 years (Musick, 1988). Mating has been observed far out in the Gulf Stream (J. A. Keinath, pers. comm.). The female is submerged while the male grasps the edge of her shell with the claws on each limb, bites at her head, and positions his cloaca next to hers (Ernst and Barbour, 1989a). Nesting along the southeastern coast of North America occurs May- August (Dodd, 1988). Known nesting dates in Virginia are from 20 June to 2 August. Nests are located above the high-tide line. Clutch size averaged 119.9 ± 17.3 eggs (87-147) for 12 nests found between 1970 and 1982 (Byles and Musick, 1981; Musick et al., 1983). Females are known to produce multiple clutches in the same season with a renesting interval of 11-20 days (Dodd, 1988), but this has not been confirmed for any Loggerhead Sea Turtles in Virginia. The spherical eggs in one nest from Back Bay National Wildlife Refuge in Virginia Beach measured 38.8-43.9 mm in diameter (ave. = 41.8 ± 0.8, n = 100) and weighed 37.2-45.8 g (ave. = 40.3 ± 1.6) (B. Jones, pers. comm.). Incubation period of one Virginia nest maintained in the laboratory was 71 days (Byles and Musick, 1981). Several nests discovered in the 1980s were on public beaches and were subsequently moved to restricted areas, such as Back Bay National Wildlife Refuge. Turtles in these nests emerged 25 August and 14 October. A hatchling was found on the beach at Back Bay National Wildlife Refuge on 11 August 1973 (Byles and Musick, 1981). Under natural conditions, nest emergence occurs at night and hatchlings make their way to the ocean, attracted by open areas of illumination (Ernst and Barbour, 1989a).

Loggerhead Sea Turtles are the most abundant species of sea turtle in the Chesapeake Bay and among the barrier islands. Estimates of 2,000 to 10,000 juveniles have been made for the bay south of the Potomac River each summer (Keinath et al., 1987; Byles, 1988). The density for the lower Chesapeake Bay was calculated at 0.15 turtle per km2 in 1982 and 0.26 per km2 in 1983 (Musick et al., 1985). The sex ratio determined from 66 dead (stranded) turtles in 1984 was 1:1.9 males to females (Bellmund et al., 1987). Sources of mortality include entanglement in gill nets, pound nets, and fishing line; propeller wounds; gunshot; disease; and shark attacks (Lutcavage, 1981; Musick et al., 1985). Between 60 and 189 dead Loggerhead Sea Turtles (ave. = 112.8 ± 41.0) were recorded in Virginia each year during 1979-1986 (Keinath et al., 1987), but these are probably underestimates. The number of strandings of C. caretta usually increased during the fall months, but declined substantially after Virginia imposed a 3-mile limit on flounder (Paralichthys dentatus) trawlers (Keinath et al., 1992). Some strandings are associated with the occurrence of giant cell meningoencephalitis, a disease of the brain causing spastic and uncoordinated movements (George et al., in press).

In the Chesapeake Bay, individuals tend to return to the same areas each year and, if displaced, will consistently return to them (Musick et al., 1985). One turtle was captured in the same area in five successive years (J. A. Keinath, pers. comm.). Once in the bay, loggerheads maintain a foraging range in the mouths of tidal rivers and never swim more than a few kilometers upstream (Byles, 1988). Tides influence turtle movement as some turtles drift with the tide, whereas others actively swim to stay in their foraging areas (Musick et al., 1985). Loggerhead Sea Turtles monitored by radio telemetry and satellite tracking moved out of the bay in the fall and moved southward along the coast. One turtle moved to north of Bermuda, south to the Gulf Stream off Georgia, and north in the Gulf Stream off Virginia (Keinath et al., 1989).

Remarks: Loggerhead Sea Turtles were occasionally mentioned in the historical literature. William Byrd II (1727) noted an abundance of these turtles and mentioned people eating the meat of the "grosskopf" (German for "big head"). Dunn (1918) first mentioned this species in the Virginia scientific literature; he listed unvouchered records from Elizabeth City (= Hampton), Norfolk, and Princess Anne (= Virginia Beach).

The anatomy of the middle ear of Loggerhead Sea Turtles was described from Virginia specimens by Lenhardt et al. (1985). They found that the middle ear is made of a bone conduction system and that it, along with the thick tympanum (outer ear drum), allows conduction of low-frequency sounds in seawater. Killingley and Lutcavage (1983) studied oxygen and carbon isotopes from barnacles on Chesapeake Bay Loggerhead Sea Turtles.

The consumption of Loggerhead Sea Turtles and their eggs for food has been reduced due to the recognition of their threatened status, but they are still eaten in many countries (see papers in Bjorndal, 1981). One Eastern Shore man, who slaughtered a loggerhead on 30 July 1988, was prosecuted by the National Marine Fisheries Service for violating the U.S. Endangered Species Act (Newport News Daily Press, 26 August 1988). Unverified reports of people occasionally eating loggerheads in Virginia persist.

The head-starting program that began on Assateague Island around 1970 (Lee, 1972) apparently failed. Several nests found in the Virginia Beach area have been transplanted since the late 1970s to Back Bay National Wildlife Refuge, where hatching success is monitored. How this program or any hatchery-based conservation program contributes to the survival of loggerheads is unknown.

Conservation and Management: The Loggerhead Sea Turtle is listed as a threatened species under the U.S. Endangered Species Act. It is illegal to molest these turtles or even to collect skulls or other parts found washed up on beaches. The research conducted by VIMS personnel continues to provide information about the life history and ecology of these turtles in Virginia. These researchers seek to identify those areas where management can help lessen the human impact. Keinath and Musick (1991a) listed the threats to this species in Virginia and discussed ways to enhance its conservation. Standings of dead turtles, nesting turtles, and observations of human interference should be reported to VIMS.

References for Life History

Photos:

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