The loggerhead sea turtle (Caretta caretta), or loggerhead, is an oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around 90 cm (35 in) long when fully grown, although larger specimens of up to 280 cm (110 in) have been discovered. The adult loggerhead sea turtle weighs approximately 135 kg (300 lb), with the largest specimens weighing in at more than 450 kg (1,000 lb). The skin ranges from yellow to brown in color, and the shell is typically reddish-brown. No external differences in gender are seen until the turtle becomes an adult, the most obvious difference being the adult males have thicker tails and shorter plastrons than the females.
The loggerhead sea turtle is found in the Atlantic, Pacific, and Indian Oceans, as well as the Mediterranean Sea. It spends most of its life in saltwater and estuarine habitats, with females briefly coming ashore to lay eggs. The loggerhead sea turtle has a low reproductive rate; females lay an average of four egg clutches and then become quiescent, producing no eggs for two to three years. The loggerhead reaches sexual maturity within 17–33 years and has a lifespan of 47–67 years.
The loggerhead sea turtle is omnivorous, feeding mainly on bottom-dwelling invertebrates. Its large and powerful jaws serve as an effective tool for dismantling its prey. Young loggerheads are exploited by numerous predators; the eggs are especially vulnerable to terrestrial organisms. Once the turtles reach adulthood, their formidable size limits predation to large marine animals, such as sharks.
Loggerheads are considered an endangered species and are protected by the International Union for the Conservation of Nature. Untended fishing gear is responsible for many loggerhead deaths. Turtles may also suffocate if they are trapped in fishing trawls. Turtle excluder devices have been implemented in efforts to reduce mortality by providing an escape route for the turtles. Loss of suitable nesting beaches and the introduction of exotic predators have also taken a toll on loggerhead populations. Efforts to restore their numbers will require international cooperation, since the turtles roam vast areas of ocean and critical nesting beaches are scattered across several countries.
The loggerhead sea turtle is the world’s largest hard-shelled turtle. Adults have an average weight range of 80 to 200 kg (180 to 440 lb) and a length range of 70 to 95 cm (28 to 37 in). The maximum reported weight is 545 kg (1,200 lb) and the maximum carapace length is 213 cm (84 in). The head and carapace (upper shell) range from a yellow-orange to a reddish-brown, while the plastron (underside) is typically pale yellow. The turtle’s neck and sides are brown on the tops and yellow on the sides and bottom.
The turtle’s shell is divided into two sections: carapace and plastron. The carapace is further divided into large plates, or scutes. Typically, 11 or 12 pairs of marginal scutes rim the carapace. Five vertebral scutes run down the carapace’s midline, while five pairs of costal scutes border them. The nuchal scute is located at the base of the head. The carapace connects to the plastron by three pairs of inframarginal scutes forming the bridge of the shell. The plastron features paired gular, humeral, pectoral, abdominal, femoral, and anal scutes. The shell serves as external armor, although loggerhead sea turtles cannot retract their heads or flippers into their shells.
Sexual dimorphism of the loggerhead sea turtle is only apparent in adults. Adult males have longer tails and claws than females. The males’ plastrons are shorter than the females’, presumably to accommodate the males’ larger tails. The carapaces of males are wider and less domed than the females’, and males typically have wider heads than females. The sex of juveniles and subadults cannot be determined through external anatomy, but can be observed through dissection, laparoscopy (an operation performed on the abdomen), histological examination (cell anatomy), and radioimmunological assays (immune study dealing with radiolabeling).
Lachrymal glands located behind each eye allow the loggerhead to maintain osmotic balance by eliminating the excess salt obtained from ingesting ocean water. On land, the excretion of excess salt gives the false impression that the turtle is crying.
The loggerhead sea turtle has a cosmopolitan distribution, nesting over the broadest geographical range of any sea turtle. It inhabits the Atlantic, Indian, and Pacific Oceans and the Mediterranean Sea.
In the Atlantic Ocean, the greatest concentration of loggerheads is along the southeastern coast of North America and in the Gulf of Mexico. Very few loggerheads are found along the European and African coastlines. Florida is the most popular nesting site, with more than 67,000 nests built per year. Nesting extends as far north as Virginia, as far south as Brazil, and as far east as the Cape Verde Islands. The Cape Verde Islands are the only significant nesting site on the eastern side of the Atlantic. Loggerheads found in the Atlantic Ocean feed from Canada to Brazil.
In the Indian Ocean, loggerheads feed along the coastlines of Africa, the Arabian Peninsula, and in the Arabian Sea. Along the African coastline, loggerheads nest from Mozambique’s Bazaruto Archipelago to South Africa’s St Lucia estuary. The largest Indian Ocean nesting site is Oman, on the Arabian Peninsula, which hosts around 15,000 nests, giving it the second largest nesting population of loggerheads in the world. Western Australia is another notable nesting area, with 1,000–2,000 nests per year.
Pacific loggerheads live in temperate to tropical regions. They forage in the East China Sea, the southwestern Pacific, and along the Baja California Peninsula. Eastern Australia and Japan are the major nesting areas, with the Great Barrier Reef deemed an important nesting area. Pacific loggerheads occasionally nest in Vanuatu and Tokelau. Yakushima Island is the most important site, with three nesting grounds visited by 40% of all nearby loggerheads. After nesting, females often find homes in the East China Sea, while the Kuroshio Current Extension’s Bifurcation region provides important juvenile foraging areas. Eastern Pacific populations are concentrated off the coast of Baja California, where upwelling provides rich feeding grounds for juvenile turtles and subadults. Nesting sites along the eastern Pacific Basin are rare. mtDNA sequence polymorphism analysis and tracking studies suggest 95% of the population along the coast of the Americas hatch on the Japanese Islands in the western Pacific. The turtles are transported by the prevailing currents across the full length of the northern Pacific, one of the longest migration routes of any marine animal. The return journey to the natal beaches in Japan has been long suspected, although the trip would cross unproductive clear water with few feeding opportunities. Evidence of a return journey came from an adult female loggerhead named Adelita, which in 1996, equipped with a satellite tracking device, made the 14500-km (9000-mi) trip from Mexico across the Pacific. Adelita was the first animal of any kind ever tracked across an ocean basin.
The Mediterranean Sea is a nursery for juveniles, as well as a common place for adults in the spring and summer months. Almost 45% of the Mediterranean juvenile population has migrated from the Atlantic. Loggerheads feed in the Alboran Sea and the Adriatic Sea. Greece is the most popular nesting site along the Mediterranean, with more than 3,000 nests per year. Because of this, Greek authorities do not allow planes to take off or land at night in Zakynthos due to the nesting turtles. In addition to the Greek coast, the coastlines of Cyprus and Turkey are also common nesting sites.
Loggerhead sea turtles spend most of their lives in the open ocean and in shallow coastal waters. They rarely come ashore, with the exception of the females’ brief visits to construct nests and deposit eggs. Hatchling loggerhead turtles live in floating mats of Sargassum algae. Adults and juveniles live along the continental shelf, as well as in shallow coastal estuaries. In the northwestern Atlantic Ocean, age plays a factor in habitat preference. Juveniles are more frequently found in shallow estuarine habitats with limited ocean access compared to non-nesting adults. Loggerheads occupy waters with surface temperatures ranging from 13.3-28.0°C (56-82°F) during non-nesting season. Temperatures from 27-28°C are most suitable for nesting females.
Juvenile loggerheads share the Sargassum habitat with a variety of other organisms. The mats of Sargassum contain as many as 100 different species of animals on which the juveniles feed. Some of the prey, such as ants, flies, aphids, leafhoppers, and beetles, are carried by the wind to these areas. Endemic prey of the mats include barnacles, small crab larvae, fish eggs, andhydrozoan colonies. Marine mammals and commercial fish, such as tuna, dolphin fish, and amberjacks, also inhabit the mats.
Ecology and Behavior;
Loggerhead sea turtles observed in captivity and in the wild are most active during the day. In captivity, the loggerheads’ daily activities are divided between swimming and resting on the bottom. While resting, they spread their forelimbs to about midstroke swimming position. They remain motionless with eyes open or half-shut and are easily alerted during this state. At night, captives sleep in the same position with their eyes tightly shut, and are slow to react. Loggerheads spend up to 85% of their day submerged, with males being the more active divers than females. The average duration of dives is 15–30 min, but they can stay submerged for up to four hours. Juvenile loggerheads and adults differ in their swimming methods. A juveniles keeps its forelimbs pressed to the side of its carapace, and propels itself by kicking with its hind limbs. As the juvenile matures, its swimming method is progressively replaced with the adult’s alternating-limb method. They depend entirely on this method of swimming by one year old.
Water temperature affects the sea turtle’s metabolic rate. Lethargy is induced at temperatures between 13 and 15°C (55 and 59°F). The loggerhead takes on a floating, cold-stunned posture when temperatures drop to around 10°C. However, younger loggerheads are more resistant to cold and do not become stunned until temperatures drop below 9°C. The loggerheads’ migration helps to prevent instances of cold-stunning. Higher water temperatures cause an increase in metabolism and heart rate. A loggerhead’s body temperature increases in warmer waters more quickly than it decreases in colder water; their critical thermal maximum is currently unknown.
Female-female aggression, which is especially uncommon in marine vertebrates, is common among loggerheads. Ritualized aggression escalates from passive threat displays to combat. This conflict primarily occurs over access to feeding grounds. Escalation typically follows four steps. First, initial contact is stimulated by visual or tactile cues. Second, confrontation occurs, beginning with passive confrontations characterized by wide head-tail circling. They begin aggressive confrontation when one turtle ceases to circle and directly faces the other. Third, sparringoccurs with turtles snapping at each other’s jaws. The final stage, separation, is either mutual, with both turtles swimming away in opposite directions, or involves chasing one out of the immediate vicinity. Escalation is determined by several factors, including hormone levels, energy expenditure, expected outcome, and importance of location. At all stages, an upright tail shows willingness to escalate, while a curled tail shows willingness to submit. Because higher aggression is metabolically costly and potentially debilitating, contact is much more likely to escalate when the conflict is over access to good foraging grounds. Further aggression has also been reported in captive loggerheads. The turtles are seemingly territorial, and will fight with other loggerheads and sea turtles of different species.
The loggerhead sea turtle is omnivorous, feeding mainly on bottom-dwelling invertebrates, such as gastropods, bivalves, and decapods. It has a greater list of known prey than any other sea turtle. Other food items include sponges, corals, sea pens, polychaete worms, sea anemones, cephalopods, barnacles, brachiopods, isopods, insects, bryozoans, sea urchins, sand dollars, sea cucumbers, starfish, fish (eggs, juveniles, and adults), hatchling turtles (including members of its own species), algae, and vascular plants. During migration through the open sea, loggerheads eat jellyfish, floating molluscs, floating egg clusters, squid, and flying fish.
Loggerheads crush prey with their large and powerful jaws. Projecting scale points on the anterior margin of the forelimbs allow manipulation of the food. These points can be used as “pseudo-claws” to tear large pieces of food in the loggerhead’s mouth. The loggerhead will turn its neck sideways to consume the torn food on the scale points. Inward-pointing, mucus-covered papillae found in the fore region of the loggerhead’s esophagus filter out foreign bodies, such as fish hooks. The next region of the esophagus is not papillated, with numerous mucosal folds. The digestion rate in loggerheads is temperature-dependent; it increases as temperature increases.
Loggerheads have numerous predators, especially early in their lives. Egg and nestling predators include oligochaete worms, beetles, fly larvae, ants,parasitoid wasp larvae, flesh flies, crabs, snakes, gulls, corvids, opossums, bears, rats, armadillos, mustelids, skunks, canids, procyonids, cats, pigs, and humans. During their migration from their nests to the sea, hatchlings are preyed on by dipteran larvae, crabs, toads, lizards, snakes, seabirdssuch as frigatebirds, and other assorted birds and mammals. In the ocean, predators of the loggerhead juveniles include fish, such as parrotfish andmoray eels, and portunid crabs. Adults are more rarely attacked due to their large size, but may be preyed on by large sharks, seals, and killer whales. Nesting females are attacked by flesh flies, feral dogs, and humans. Salt marsh mosquitos can also pester nesting females.
In Australia, the introduction of the red fox (Vulpes vulpes) by English settlers in the 19th century led to significant reductions in loggerhead sea turtle populations. In one coastal section in eastern Australia during the 1970s, predation of turtle eggs destroyed up to 95% of all clutches laid. Aggressive efforts to destroy foxes in the 1980s and 1990s has reduced this impact; however, it is estimated that it will be the year 2020 before populations will experience complete recovery from such dramatic losses.
Along the southeastern coast of the United States, the raccoon (Procyon lotor) is the most destructive predator of nesting sites. Mortality rates of nearly 100% of all clutches laid in a season have been recorded on some Florida beaches. This is attributed to an increase in raccoon populations, which have flourished in urban environments. Aggressive efforts to protect nesting sites by covering them with wire mesh has significantly reduced the impact of raccoon predation on loggerhead sea turtle eggs. On Bald Head Island in North Carolina, wire mesh screens are used on every confirmed nest to prevent excavation by resident red foxes. A new concern with the steel cage technique is interference with the normal development of the nestlings’ magnetic sense due to the use of ferrous wire, which may disrupt the turtles’ ability to navigate properly. Efforts are underway to find a nonmagnetic material that will prevent predators gnawing through the barrier.
Up to 40% of nesting females around the world have wounds believed to come from shark attacks.
Female loggerheads first reproduce between the ages of 17 and 33, and their mating period may last more than six weeks. They court their mates, but these behaviors have not been thoroughly examined. Male forms of courtship behavior include nuzzling, biting, and head and flipper movements. Studies suggest females produce cloacal pheromones to indicate reproductive ability. Before mating, the male approaches a female and attempts to mount her, while she resists. Next, the male and female begin to circle each other. If the male has competitors, the female may let the males struggle with each other. The winner then mounts the female; the male’s curved claws usually damage the shoulders of the female’s shell during this process. Other courting males bite the male while he is attempting to copulate, damaging his flippers and tail, possibly exposing bones. Such damage can cause the male to dismount and may require weeks to heal. While nesting, females produce an average of 3.9 egg clutches, and then become quiescent, producing no eggs for two to three years. Unlike other sea turtles, courtship and mating usually do not take place near the nesting beach, but rather along migration routes between feeding and breeding grounds. Recent evidence indicates ovulation in loggerheads is mating-induced. Through the act of mating, the female ovulates eggs which are fertilized by the male. This is unique, as mating-induced ovulation is rare outside of mammals. In the Northern Hemisphere, loggerheads mate from late March to early June. The nesting season is short, between May and August in the Northern Hemisphere and between October and March in the Southern Hemisphere.
Loggerheads may display multiple paternity. Multiple paternity is possible due to sperm storage. The female can store sperm from multiple males in her oviducts until ovulation. A single clutch may have as many as five fathers, each contributing sperm to a portion of the clutch. Multiple paternity and female size are positively correlated. Two hypotheses explain this correlation. One posits that males favor large females because of their perceived higher fecundity (ability to reproduce). The other states, because larger females are able to swim more quickly to mating grounds, they have longer mating periods.
All sea turtles have similar basic nesting behaviors. Females return to lay eggs at intervals of 12–17 days during the nesting season, on or near the beach where they hatched. They exit the water, climb the beach, and scrape away the surface sand to form a body pit. With their hind limbs, they excavate an egg chamber in which the eggs are deposited. The females then cover the egg chamber and body pit with sand, and finally return to the sea. This process takes one to two hours, and occurs in open sand areas or on top of sand dunes. The nesting area must be selected carefully because it affects characteristics such as fitness, emergence ratio, and vulnerability to nest predators. Loggerheads have an average clutch size of 112.4 eggs.