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 centimetres (35 in) long when fully grown, although larger specimens of up to 270 centimetres (110 in) have been discovered. The adult loggerhead sea turtle weighs approximately 135 kilograms (300 lb), with the largest specimens weighing in at more than 454 kilograms (1,000 lb). The skin ranges from yellow to brown in color, and the shell is typically reddish-brown. There are no external differences in gender until the turtle becomes an adult, the most obvious difference being that 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 in 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 organisms 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 (TEDs) have been implemented in efforts to reduce mortality by providing the turtle an escape route. Loss of suitable nesting beaches and the introduction of exotic predators has 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 among several countries.
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 °C (56–82 °F) during non-nesting season. Temperatures from 27–28 °C (81–82 °F) 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 Sargassum mats include barnacles, small crab larvae, fish eggs, and hydrozoan colonies. Marine mammals and commercial fish, such as tuna, dolphin fish, and amberjacks, also inhabit the Sargassum mats.
The loggerhead sea turtle has a cosmopolitan distribution, nesting over the broadest geographical range of any sea turtle. The loggerhead 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 over 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 Extension 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 (individuals past the juvenile stage that lack adult characteristics). 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, who in 1996, equipped with a satellite tracking device, made the 9,000-mile (14,000 km) 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.
These turtles occur every once and a while on the British coasts.
All modern sea turtles probably descended from a single common ancestor during the Cretaceous period; however, evidence of a specific ancestor is lacking. Loggerheads, like all other sea turtles excluding the leatherback sea turtle, are members of the ancient family Cheloniidae. About 40 million years ago, a branch of the Cheloniidae gave rise to loggerhead sea turtle. Of the six species of living Cheloniidae, loggerheads are more closely related to the Kemp's ridley sea turtle, olive ridley sea turtle, and the hawksbill turtle than they are to the flatback turtle and the green turtle.
Around three million years ago, during the Pliocene epoch, Central America emerged from the sea, effectively cutting off currents between the Atlantic and Indo-Pacific Oceans. The rerouting of ocean currents lead to climatic changes as the Earth entered a glacial cycle. Cold water upwelling around the Cape of Good Hope and reduction in water temperature at Cape Horn formed cold water barriers to migrating turtles. The result was a complete isolation of the Atlantic and Pacific populations of loggerheads. During the most recent ice age, the beaches of southeastern North America were too cold for sea turtle eggs. As the Earth began to warm, loggerheads moved farther north, colonizing the northern beaches. Because of this, turtles nesting between North Carolina and northern Florida represent a different genetic population from those in southern Florida.
The distinct populations of loggerheads have unique characteristics and genetic differences. For example, Mediterranean loggerheads are smaller, on average, than Atlantic Ocean loggerheads. North Atlantic and Mediterranean loggerhead sea turtles are descendants of colonizing loggerheads from Tongaland, South Africa. South African loggerhead genes are still present in these populations today.
Anatomy and morphologyEdit
The turtle's shell is divided into two sections: carapace and plastron. The carapace is further divided into large plates, or scutes. Typically, there are 11 or 12 pairs of marginal scutes which 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 3 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 head or flippers into their shells.The loggerhead sea turtle is the world's largest hard-shelled turtle. Adult loggerheads have an average weight range of 80 to 200 kilograms (180 to 440 lb) and a length range of 70 to 95 centimetres (28 to 37 in). The maximum reported weight is 545 kilograms (1,200 lb) and the maximum carapace length is 213 centimetres (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.
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 carapace 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.
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 approximately 10 °C (50 °F). However, younger loggerheads are more resistant to cold and do not become stunned until temperatures drop below 9 °C (48 °F). The loggerheads' migration help 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. The loggerhead sea turtle's critical thermal maximum is currently unknown. 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, loggerheads spread their forelimbs to about mid-stroke swimming position. They remain motionless with eyes open or half-shut and are easily alerted during this state. At night, captive loggerheads 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 minutes, but they can stay submerged for up to four hours. Juvenile loggerheads and adults differ in their swimming methods. Juveniles keep their forelimbs pressed to the side of their carapace and propel themselves by kicking with their hind limbs. As the juveniles mature, their swimming method is progressively replaced with the adults' alternating-limb method. The loggerheads depend entirely on this method of swimming by the time they are one year old.
Female-female aggression, being uncommon (especially 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, sparring occurs 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.
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. Loggerheads have numerous predators. Egg and nestling predators include oligochaete worms, beetles, fly larvae, ants, parasitoid wasp larvae,flesh flies, crabs, snakes, gulls, crows, opossums, bears, rats, armadillos, honey badgers, skunks, canids, raccoons, cats, hogs, and humans. During their migration from their nest to the sea, hatchlings are preyed on by dipteran larvae, crabs, toads, lizards, snakes, birds, and mammals. In the ocean, predators of the loggerhead juveniles and adults include sharks, other fish, such as parrotfish, moray eels, portunid crabs, gulls, monk seals, and killer whales. Nesting females are attacked by flesh flies, feral dogs, and humans. Salt marsh mosquitoes can also pester nesting females.
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 predator's gnawing through the barrier.
Up to 40% of nesting females around the world have wounds believed to come from shark attacks.
Dieseses and parasites
Infectious bacteria such as Pseudomonas and Salmonella attack loggerhead hatchlings and eggs. Fungi such as Penicillium infect loggerhead sea turtle nests and cloaca.
Fibropapillomatosis disease threatens loggerheads in the form of the herpes-type virus which causes internal and external tumors. These tumors disrupt essential behaviors and, if on the eyes, cause permanent blindness. Trematodes of the family Spirorchiidae inhabit tissues throughout the body of the loggerhead, including vital organs such as the heart and the brain. Trematode infection can be highly debilitating. For example, inflammatory trematode lesions can cause endocarditis and neurological disease. A nematode, Angiostoma carettae, also infects loggerheads. The nematodes cause histologic lesions in the respiratory tract.
More than 100 species of animals from 13 phyla as well as 37 kinds of algae live on loggerheads' backs. These parasitic organisms, which increase drag, offer no known benefit to the turtle, although it has been suggested that the dulling effect of organisms on shell color improves camouflaging ability.
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, mucosal (mucus-covered) papillae found in the foreregion of the loggerhead's esophagus filter out foreign bodies, such as fish hooks. The next region of the esophagus is nonpapillated, with numerous mucosal folds. The rate of digestion in loggerheads is temperature dependent; digestion rate increases as temperature increases. The loggerhead sea turtle is omnivorous, feeding mainly on bottom dwelling invertebrates, such as gastropods, bivalves, and decapods. The loggerhead 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), wrasses, 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.
After incubating for approximately 80 days, hatchlings dig through the sand to the surface. This usually occurs at night, when darkness increases the chance of escaping predation and damage from extreme sand surface temperatures is reduced. Hatchlings enter the ocean by navigating toward the brighter horizon created by the reflection of the moon and star light off the water's surface. Hatchlings range in color from light brown to almost black, lacking the adult's distinct yellows and reds. Upon hatching, they measure approximately 4.6 centimetres (1.8 in) and weigh about 20 grams (0.71 oz). The eggs are typically laid on the beach in an area above the high-tide line. The eggs are laid near the water so the hatchlings can return to the sea. The loggerhead's sex is dictated by the temperature of the underground nest. Incubation temperatures generally range from 26–32 °C (79–90 °F). Studies show loggerhead sea turtle eggs kept at a constant incubating temperature of 32 °C (90 °F) become females. Eggs incubating at 28 °C (82 °F) become males. An incubation temperature of 30 °C (86 °F) results in an equal ratio of male to female hatchlings. Hatchlings from eggs in the middle of the clutch tend to be the largest, grow the fastest, and be the most active during the first few days of sea life.
Hatchlings can lose up to 20% of their body mass due to evaporation of water as they journey from nest to ocean. Hatchlings initially use the undertow to push them five to ten yards away from the shore. Once in the ocean, hatchlings swim for about 20 hours, bringing them far offshore.An iron compound, magnetite, in their brains allows the turtles to perceive the Earth's magnetic field, for navigation. Many hatchlings use Sargassumin the open ocean as protection until they reach 45 centimetres (18 in). Hatchling loggerheads live in this pelagic environment until they reach juvenile age, and then they migrate to nearshore waters.
Like all marine turtles, the loggerhead prepares for reproduction in its foraging area. This takes place several years before the loggerhead migrates to a mating area. Female loggerheads first reproduce at ages 28–33 in Southeastern United States and Australia, and at ages 17–30 in South Africa. Age at first reproduction in the Mediterranean, Oman, Japan, and Brazil are unknown. Nesting loggerheads have a straight carapace length of 70–109 centimetres (28–43 in). Because of the large range, carapace length is not a reliable indicator of sexual maturity. Loggerheads have an estimated maximum lifespan of 47–67 years in the wild. When ocean waters cool, loggerheads must migrate to warmer areas or hibernate to some degree! In the coldest months, loggerheads submerge for up to seven hours at a time, emerging for only seven minutes to breathe. Although outdone by freshwater turtles, these are among the longest recorded dives for any air-breathing marine vertebrate. During their seasonal migration, juvenile loggerheads have the ability to use both magnetic and visual cues. When both aids are available, they are used in conjunction; if one aid is not available, the other suffices. The turtles swim at about 1.6 kilometres per hour (0.44 m/s) during migration.
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 states that males favor large females due to perceived higher fecundity (ability to reproduce). The other states that because larger females are able to swim more quickly to mating grounds, they have a longer mating period. Female loggerheads first reproduce between the ages of 17 and 33, and their mating period lasts up to six weeks. They court their mates, however 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 an average of 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 Mediterranean, loggerheads mate from late March to early June. The nesting season peaks in June and July, but varies by nesting beach.
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 4 eggs.
Many human activities have negative effects on loggerhead sea turtle populations. The prolonged time required for loggerheads to reach sexual maturity and the high mortality rates of eggs and young turtles from natural phenomena compound the problems of population reduction as a consequence of human activities.