Caretta caretta

Geographic Range

Caretta caretta is found in nearly all the world's temperate and tropical oceans: the Atlantic Ocean from Newfoundland to Argentina, the Indian Ocean from southern Africa to the Arabian Gulf to western Australia, the Mediterranean Sea, and the Pacific Ocean from Alaska to Chile and Australia to Japan. During winter months loggerhead sea turtles migrate to tropical and subtropical waters.

• Biogeographic Regions
• indian ocean
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native
• mediterranean sea
  • native native

Habitat

Preferred habitat of Caretta caretta individuals changes throughout the life cycle. Adult females go ashore to lay eggs and seem to prefer steeply sloped, high energy beaches. When hatchlings emerge from the nest, they head for the ocean. Young juveniles are typically found among drifting Sargassum mats in warm ocean currents. Older juveniles and adults are most often found in coastal waters and tend to prefer a rocky or muddy substrate over a sandy one. They may also be found near coral reefs and venturing into salt marshes, brackish lagoons, and the mouths of rivers.

• Habitat Regions
• temperate temperate
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• reef reef
• coastal coastal
• brackish water brackish water

• Other Habitat Features
• estuarine estuarine

Physical Description

Named for their huge heads and powerful jaws, loggerhead turtles are the largest hard-shelled sea turtles alive today. They have a heart-shaped carapace, which is often covered with commensal organisms such as barnacles and algae. Generally, the carapace is a reddish-brown hue with olive tones; there are five pairs of pleural scutes, the first pair touching the cervical (neck) scute. The plastron is cream to yellow, and has two longitudinal ridges that disappear with age. The skin is dull to reddish brown dorsally and medium to pale yellow around the edges and ventrally. The skin may have some orange coloration as well. The skin of males is more brown and the head more yellow than those of females. Males also have wider carapaces and a long curved claw on each forelimb. Loggerhead sea turtle hatchlings tend to be dark brown to reddish brown on the carapace and cream to reddish brown or dark brown on the plastron. The average adult Caretta caretta in the Mediterranean Sea is smaller than the average adult in the Atlantic Ocean. Two subspecies - C. caretta gigas in the Pacific and Indian Oceans and C. caretta caretta in the Atlantic - have been proposed but are not fully accepted. They differ in the number of neural bones in the carapace and marginal scutes on the edge of the carapace. Loggerhead sea turtles differ from other sea turtles in having relatively large heads and reddish coloration. Additionally, Ridley's sea turtles ( Lepidochelys ) have four inframarginal scutes on the bridge. Green sea turtles ( Chelonia mydas ) and hawksbill sea turtles ( Eretmochelys imbricata ) have only four pairs of pleural scutes on the carapace; the first pleurals do not touch the cervical scute.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes colored or patterned differently
• sexes shaped differently

Development

Like many turtles, Caretta caretta has temperature-dependent sex determination (TSD). The sex of hatchlings is determined by egg temperature during the middle third of incubation. The pivotal temperature - the temperature at which an 50:50 ratio of males:females is produced - varies from location to location around the world. For example, the pivotal temperature in South Africa is 29.7 ºC , but in Australia the pivotal temperature is 28.2 ºC. Generally, the pivotal temperature is between 28 and 30 ºC. Temperatures of 24 to 26 ºC tend to produce all males and temperatures of 32 to 34 ºC tend to produce all females. Eggs are not viable outside the extremes of these ranges.

The speed of embryonic development within the egg depends on the temperature within the nest. This temperature can be affected by sun, shade, rain, heat generated within the nest, and an egg's position in the nest. At cool temperatures, around 25 ºC, development to hatching can take 65 to 70 days, but at warmer temperatures, around 35 ºC, development usually takes around 45 days.

When loggerheads are juveniles the differences between the sexes begin to emerge. Males produce increasing levels of testosterone as they approach maturity, which triggers tail growth, plastron softening, and the growth and curvature of a nail on each forelimb. Females produce estrogen and small amounts of testosterone, but externally just grow larger. Age at maturity is variable. Mature size is attained between age 10 and 30; captives are predicted to mature in 16 to 17 years. Reproductve life span (after reaching maturity) is estimated at about 32 years.

• Development - Life Cycle
• temperature sex determination

Reproduction

Just before the nesting season, male loggerhead sea turtles migrate to mating grounds, which are usually located offshore from nesting beaches. They wait for females to begin courtship and mating. A male will circle a female, then approach her and bite her neck or shoulder. He will then attempt to mount her and, if she accepts him, they will mate. If a female does not accept the male she covers her cloaca and swims to the bottom, but a persistent male may wait until she needs air and make another attempt. Males use the long, curved claws on their forelimbs to hold on because mating may last for hours and other males often ram and bite the mating male, attempting to dislodge him. If a male is dislodged, another may quickly replace him.

During the nesting season a female may lay several clutches, and will re-mate each time. In some cases, she may mate several times between clutches and so a single clutch may have sperm contributed by several males.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Peak mating season for Caretta caretta occurs in the early summer months. During this time, males remain in the waters offshore of the nesting beach, while females alternate between mating in the water, nesting on land, and feeding in estuaries and reefs. A female will nest every 12 to 17 days, or 2 to 5 times, during the breeding season. For each nest she must drag herself onto land, where she is in much greater danger of predation, and excavate a nest. Into this nest she lays 110 to 130 round eggs. The eggs incubate for 45 to 80 days, depending on temperature. Loggerhead sea turtles reach sexual maturity at carapace lengths longer than 90 cm, which can occur between 10 and 30 years of age.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Parental energy investment in loggerhead sea turtles is largely pre-ovipositional, there is no parental care of young. Females provide nutrition in the form of yolk which is used by embryos for growth and development; residual yolk can probably support a hatchling for several days or weeks. Females also expend considerable energy when migrating to nesting beaches and in the ovipositional (nesting/ egg laying) process. Male investment is largely during courtship and mating, and in sperm production.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

Not much is known about the lifespan of Caretta caretta . Is is estimated that they live 30 to 62 years in the wild, but data is insufficient for lifespan in captivity as well as longest known lifespans in the wild and in captivity. In Australia is has been predicted that the annual survival rate is 92% for immature individuals and 88% for adults.

Behavior

As a marine species, loggerhead sea turtles have some special adaptations. They have salt glands near their eyes, which allow them to drink sea water and excrete salt in high concentrations. Many people have seen nesting females supposedly "crying" for their young, but they are simply excreting excess salt. Loggerhead sea turtles are able to hold their breath for long periods of time. Though a typical dive lasts only 4 to 5 minutes, loggerheads are capable of diving for up to 20 minutes and can rest for hours without breathing. As a general rule, males are more active swimmers than females.

Loggerhead sea turtles are known for their migratory behavior. Some individuals have been recorded migrating up to 4,828 km. Adults and juveniles in temperate waters migrate towards the equator for winter to avoid cold stunning in waters under 10 ºC. Cold stunning occurs in sea turtles that find themselves in waters under 10 ºC, they become lethargic and float on the surface. If the water temperature drops below 5 ºC, the turtles could die.

• Key Behaviors
• natatorial natatorial
• motile motile
• migratory migratory
• solitary solitary

Home Range

Loggerhead sea turtles are migratory and does homing abilities. As juveniles, the home range is their feeding grounds. There is some evidence that feeding grounds are chosen near the natal nest site, known as natal homing. Juveniles removed from their feeding grounds will quickly make their way back. Adults tend to return to the same nesting grounds year after year and many return to the very beach where they themselves hatched.

Communication and Perception

Communication in Caretta caretta has not been well-studied. Courtship behavior seems to largely depend on visual and tactile cues, but it has been suggested that glandular odors (especially Rathke's gland secretions) may help bring the sexes together.

Perception, however, is highly developed. As soon as hatchlings emerge from their nests (usually at night), they begin analyzing their environment to determine which direction they should go towards the ocean. It is believed that a major clue is the light on the horizon. Hatchlings orient towards the brightest light, which, historically, is the moon or star light over the ocean. They may also perceive the incline of the beach and orient towards a lower elevation. Once in the water, hatchlings use chemical and magnetic cues to orient themselves and navigate their way to the currents in which they will spend the next 10 or so years of their lives.

During the juvenile and adult years it is likely that loggerheads use chemical and magnetic cues to orient themselves during their migrations. It has been demonstrated that C. caretta uses on-site cues, not memory of past movement, in orientation and is therefore capable of map-based navigation.

Food is typically located either visually or by smell.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• polarized light polarized light
• tactile tactile
• vibrations vibrations
• chemical chemical
• magnetic magnetic

Food Habits

Loggerhead sea turtles are primarily carnivorous, but will also eat algae - Ascophyllum , Ulothrix , Urospora , Sargassum - and vascular plants - Cymodocea , Thalassia , Zostera - making them omnivorous. Their huge heads and massive, powerful jaws make them well-adapted to eating hard-shelled prey, such as horseshoe crabs ( Limulus polyphemus ), bivalves, barnacles, whelks, and conchs. However, Caretta caretta is a dietary generalist and also eats many other invertebrates, such as sponges, jellyfish, cephalopods, shrimp, insects, sea urchins, and fish and fish eggs, including Brecoortia species, Ceratoscopelus species, and Diodon species. There are slight variations in the diet of each life stage, but loggerhead sea turtles are generalists throughout life.

• Primary Diet
• omnivore omnivore

• Animal Foods
• fish
• eggs
• insects
• mollusks
• aquatic or marine worms
• aquatic crustaceans
• echinoderms
• cnidarians
• other marine invertebrates

• Plant Foods
• leaves
• algae
• macroalgae macroalgae

Predation

Most turtles are able to withdraw into their shell as a means of escaping a predator. No sea turtle is able to do this. Loggerhead sea turtles have their hard shell, their size, and their rough, scaly skin on the head and neck to protect them from predation. These defenses are usually sufficient for adults and larger juveniles, but these turtles are sometimes preyed on by sharks and killed by humans. Hatchlings and eggs have many predators and few defenses. Females try to disguise newly laid nests as much as possible, but they still suffer high predation rates. Raccoons ( Procyon lotor ) in U.S. can destroy up to 80% of nests on some beaches. Red foxes ( Vulpes vulpes ) in Australia may destroy 90 to 95% of nests. In some areas of the world human predation on nests is substantial. Hatchlings generally emerge from the nest at night to lessen chances of predation, but many are then taken by crabs, birds ( gulls , frigate birds , vultures , crows , etc.), raccoons , canids (foxes, dogs, etc.), and carnivorous fish.

Ecosystem Roles

Caretta caretta has been called a "keystone species" because of its ecological impact. It feeds on large numbers of invertebrates, affecting their populations and allowing their broken shells to be used as a calcium source for other species. Also, a substantial portion of the eggs laid become food for predators. Finally, over 100 species from 13 phyla may live on the carapace of loggerheads, making it somewhat of a mobile reef.

• Ecosystem Impact
• creates habitat
• keystone species keystone species

Economic Importance for Humans: Positive

Caretta caretta is beneficial to humans in many ways. Sea turtles are an attraction for ecotourism and popular with people wanting to snorkel or dive with these animals, as well as for those wanting to watch the nesting process. Loggerhead sea turtles are the most common sea turtle in U.S. waters and therefore most sea turtle research is carried out on this species. Also, in many countries, especially in Central and South America, Africa, Asia, and the Mediterranean, these turtles and their eggs are exploited for food.

• Positive Impacts
• food food
• body parts are source of valuable material
• ecotourism ecotourism
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Caretta caretta on humans.

Conservation Status

Caretta caretta , like all sea turtle species, is in decline. The greatest causes of decline world-wide is probably incidental capture in fishing gear such as long lines, gill nets, shrimp trawls, and direct exploitation of adult turtles and eggs for human food. Though in sharp decline in many parts of its range, and locally along North American coasts, loggerhead sea turtles are currently the most common and least-threatened marine turtle in North American waters. They are listed as threatened under the U.S. Endangered Species Act.

Other important causes of decline include beachfront development, human disturbance of nesting females, pesticides, petroleum products (oil spills), and other ocean pollutants, human-influenced increases in nest predators such as raccoons, collisions with watercraft, and offshore and channel dredging. Artificial lighting near beaches can confuse emerging hatchlings, causing them to move away from the ocean and into hazardous urban areas. If predictions about global warming are realized, increased storms and rising sea levels could damage or destroy nesting areas and nests, and temperature changes could skew sex ratios.

The United States has taken several measures to reduce bycatch of loggerhead sea turtles. Turtle exclusion devices (TEDs) are required in commercial fishing and shrimping nets. There have been other gear modifications, changes in practice, and area closures in fishing that have reduced bycatch. Also, other countries may harvest shrimp in a way that puts loggerhead sea turtles in danger and the U.S. has put an embargo on these shrimp. Despite these measures being taken, the numbers of loggerhead sea turtles in U.S. waters is still declining.

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Liz Duermit (author), Michigan State University, James Harding (editor, instructor), Michigan State University.

References

Avens, L., J. Braun-McNeill, S. Epperly, K. Lohmann. 2003. Site fidelity and homing behavior in juvenile loggerhead sea turtles (Caretta caretta). Marine Biology , 143: 211-220.

Avens, L., K. Lohmann. 2004. Navigation and seasonal migratory orientation in juvenile sea turtles. Journal of Experimental Biology , 13: 1771-1778.

Bowen, B., A. Bass, S. Chow, M. Bostrum, K. Bjorndal, A. Bolten, O. Toshinori, B. Bolker, S. Epperly, E. LaCasella, D. Shaver, M. Dodd, S. Hopkins-Murphy, J. Musick, M. Swingle, K. Rankin-Baransky, W. Teas, W. Witzell, P. Dutton. 2004. Natal homing in juvenile loggerhead turtles. Molecular Ecology , 13: 3797-3808.

Dodd, C. 1988. Synopsis of the biological data on the loggerhead sea turtle Caretta caretta (Linnaeus 1758).. U.S. Fish and Wildlife Service Biol. Report , 8 (14): 1-110.

Ernst, C., R. Barbour, J. Lovich. 1994. Turtles of the United States and Canada . Washington and London: Smithsonian Institution Press.

Limpus, C. 1985. A study of the loggerhead sea turtle, Caretta caretta , in eastern Australia. PhD Dissertation. . St. Lucia, Australia: University of Queensland.

Spotila, J. 2004. Sea Turtles: A complete guide to their biology, behavior, and conservation . Baltimore, Maryland: The Johns Hopkins University Press and Oakwood Arts.

2006. "MarineBio" (On-line). Carretta caretta, Loggerhead Sea Turtle. Accessed October 07, 2006 at http://marinebio.org/species.asp?id=163 .

2006. "NOAA Fisheries" (On-line). Loggerhead Turtle (Caretta caretta). Accessed October 07, 2006 at http://www.nmfs.noaa.gov/pr/species/turtles/loggerhead.htm .