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Turtle distribution

Species outlines

Loggerhead sea turtle - Caretta caretta

Browse through Outlines

Picture of Loggerhead Sea Turtle

Size and body mass

Diagnostic features

Geographical distribution

Habitat and Biology

Typical habitats

Migration

Nesting areas

Nesting periods

Nesting behaviour

Egg number, size and weight

Incubation timing

Size and weight of hatchlings

Maturity

Courtship and mating

Sex determination

Hatching

Egg mortality and predation

Hatchling mortality and predation

Commensalism and disease

Feeding

Threats to survival

Caretta caretta

En - Loggerhead turtle; Fr - Tortue caouanne; Sp - Caguama

Size (cm) and body mass (kg):

Normal variation in Straight Carapace Length (SCL) for a mature female:

81.5-105.3 cm; n=3502 ( n=number in sample)

The SCL for mature females is always over 70 cm.

World variation: figures, unless stated, are for mature females

USA (South Carolina) 84.5-103 cm: mean 92.7 cm: n=18

USA (Georgia) mean 95.9 cm: n=110

USA (Florida) 74.9-109.2 cm: mean 92 cm: n=661

USA (Broward county) mean 99.6 cm: n=1203

Mexico (Quintana) 73-109cm: mean 90.5 cm: n=423 (females)

Mexico (Quintana) 75.3-99.5 cm: mean 86.5 cm: n=39 (males)

Colombia (Buritaca) 70-102 cm: mean 87.9cm: n=77

Greece (Zakynthos) 70-93 cm:mean 81.5 cm: n=95

Greece (Kiparissa) mean 78.6 cm: 69-91 cm: n=68 (Margaritoulis, 1987)

Greece (SE Cephalonia) mean 76.6 cm: n=25 (Whitmore, C., pers. comm via Groombridge)

Turkey (Dalyan) 55-74.6 cm (Geldiay et al., 1982) - males and females caught at sea

Spain (Balearics) 30-65 cm: n.b. caught on longlines at sea (Mayol & Castello Mas, 1983)

South Africa (Tongaland) 72.8-98.5 cm: mean 86.4 cm: n=1182

South Africa (Natal) 75.2-90.5 cm: mean 81.6 cm: n=13

Oman (Masirah islands) mean 91.2 cm : n=1378

Australia (Heron islands) 86-102 cm: n=?

Japan (Shikoku) 72-107.5 cm: mean 89 cm: n=118

Overall body mass in Kg:

65.7-101.4 kg: mean 75 kg: n=153

World variation:

Mexico (Quintana Roo) mean 65.7 kg: n=115 (females)

Mexico (Quintana Roo) mean 101.4 kg: n=38 (males)

Mediterranean (all) mean 105 kg: n=? (females)

Greece (SE Cephalonia) mean 68 kg: 52-84 kg: n=12 (Whitmore, C., pers. comm via Groombridge)

South Africa (Tongaland) mean 106.9 kg: n=31 (females)

South Africa (Tongaland) mean 68 kg: n=13 (males)

Diagnostic features:

• Heart shaped carapace, its width about 80% of its length.
• Head is large and broad and takes up 25% of carapace length.
• Strong horny beak and thicker than other sea turtles.
• Carapace scutes are thin but very hard and rough, often covered in barnacles.
• Five central plates or scutes.
• Fore flippers quite short and thick, each with 2 claws.
• Rear flippers have 2 or 3 claws.
• Hatchlings and juveniles have 3 keels down carapace length formed from blunt spines
• Colour

  Adults are generally evenly covered on the top (dorsal) side.

  Top colour is reddish brown with dark streaks in South African turtles.

  Orange-cream on their flanks

  Orange-cream on underside

  Hatchlings are dark-brown on top with pale brown margins to flippers and underside

Geographical Distribution:

• Widely distributed in coastal tropical and subtropical waters (16-20 degrees C).
• Loggerheads can wander into temperate waters to the edge of warm currents.
• Some can migrate long distances in warm currents - Gulf Stream in the Northern Atlantic.
• They can survive in a variety of different environments e.g.
  Brackish water of coastal lagoons and river mouths; open sea.
• Often get spring-summer feeding grounds for juveniles, sub-adults and some adults.
• In the winter, they can remain buried in the mud of quite deep water.
• Limit of distribution is temperature dependent.
• Rarely survives in water below 10 degrees C.
• In cold waters they become stunned and drift helplessly.
• In some warm years they can get into northern waters e.g. Murmansk and Barent Sea.

Click here to go to World Distribution Maps

Habitat and Biology:

Typical habitats:

Mainly found on the continental shores of warm, shallow seas. Also found around some islands such as Zakynthos in Greece. Most aggregate just off nesting beaches prior to the nesting season (the time varies greatly depending on location). Loggerheads are the only Sea Turtles that can nest successfully outside of the tropics although the water temperature has to be above 20 degrees C.

Migrations:

After nesting, adults disperse to feeding grounds. Outside of the Mediterranean, migratory routes are not clearly defined although hatchlings are thought to follow the warm currents such as the Gulf Stream. Hatchlings and juveniles often congregate at sea fronts (the meeting of oceanic currents) where food and floating animals gather. Even some suggestions that they get trapped in these currents and only emerge back on their natal beaches once the circuit has been completed - mature and ready to breed!

Loggerheads can migrate across large distances: one that had nested and been tagged on a beach in Florida was recaptured less than 10 months later, 2,400 km away in the Dominican Republic!

The time elapsed (a year or more) that the hatchlings stay feeding in these areas are called the Lost years. They are thought to drift within the large mats of sargassum weed.

Mediterranean loggerheads rarely leave their enclosed sea and are thought to be a genetically isolated population. There is some evidence of recruitment via Gibralter and Suez, although this is probably very small. Loggereheads are found all over the Mediterranean although most activity occurs in the Eastern part of the Mediterranean and there is firm evidence that there are important wintering areas located off the south east coast of Turkey (Groombridge).

Nesting areas:

Outside of the Mediterranean, there are several major nesting grounds. The major part of the world's nesting sites are located in Southeastern USA with annual nest counts of 28,000 and Oman with 30,000. Elsewhere, there are 2,000 nests in Brazil, 1,000 in South Africa and 2,000 in Australia: smaller nesting sites also exist in numerous other locations. Nests in the Indian Ocean are virtually unknown.

In the Mediterranean, the loggerhead is the commonest nesting turtle with Greece hosting the highest nesting populations of 2,000+. Sekania beach on Zakynthos Island, Greece has the highest density of nests anywhere in the world. Recent surveys have also shown significant nest numbers in Turkey and Libya.

Nesting periods:

This usually occurs in spring or summer, depending upon location.

Caribbean - April to early August

NW Atlantic - April to September

SW Atlantic - April to August

Eastern Mediterranean - June to September

Senegal - July to October

South Africa - October - February

China - April to August

Australia - October to April

Nesting behaviour:

The female usually come ashore at night ( records suggest that this may well have happened during the day in undisturbed sites). Loggerheads are said to be highly philopatric: returning to the same stretch of coastline to nest each year, probably to the same area where they originally hatched. Some populations are more site specific than others. Nesting sites are only found on sandy, shelving beaches. The nest is usually made at the top of the beach and about 45 cm deep and flask shaped. After laying, she will cover the nest with sand and attempt to camouflage by scattering sand. She will then return to the sea. Loggerheads have a characteristic track as shown in the picture below.

Track is wavy with alternate flipper marks. The outlines are marked in white.
The turtle is moving down the picture!

If you are viewing this page with a browser that supports multi-part GIF sequences (ie Netscape V2 or better), click on the picture to the right of turtle tracks to see an animated nesting sequence. The sequence shows a female camouflaging her nest after egg laying, and her return to the sea.

Egg number, size and weight:

Most females nest between 2 or 3 times in a season, with a gap of about 14 days between each laying. They lay 40 to 190 eggs, depending on the individual. A single female could lay 560 eggs per season. The reproductive cycle using involves laying every two or three years although some will lay every year. Clutch sizes vary greatly as shown below.

USA (N. Carolina) mean 123: 86-159 eggs: n=36

USA (S. Carolina) mean 126: 64-198 eggs: n=71

USA (Georgia) mean 120 eggs: n=2827

USA (Florida) mean 107: 53-174: n=1928

USA (Merrit Island) mean 12: 82-173: n=64

Greece (Zakynthos) 52-114 eggs

Turkey (Med. coast) mean 93: 55-160: n=50

Egg size is usually proportional to the size of the turtle e.g. smaller eggs from smaller turtles.

Mean diameter ranges from 34.7-55.2 mm.

Eggs in one clutch are very similar in size although a few can be smaller. This contrasts to the Leatherback Sea Turtle, which has a great variation in egg size within one clutch.

Egg weight varies from 26.2-46.8 g.

Eggs shed by female in Laganas Bay, Zakynthos - Greece

Incubation time:

Incubation time varies with beach latitude.

USA (Florida) mean 68 days (Lat-26)

Mexico (Quintano Roo) mean 56 days (Lat-19)

Turkey (Med. coast) mean 57 days (Lat-36)

Greece (Zakynthos) mean 57 days (Lat-38)

South Africa (Tongaland) mean 68 days (Lat-30)

Japan (Hiwasa) mean 58 days (Lat-34)

There is some considerable degree of variation on any one beach, due to local environmental conditions. Some sites also show considerable variation from one year to the next.

Size and weight of hatchlings:

Size and weight of the hatchlings correlates directly to the egg size. The mean Straight Carapace Length (SCL) ranges from 33.5-55 mm. Weights vary between 18.8-21.1 g.

Maturity:

The age of first maturity is not clear but research in captive specimens suggests between 6 to 20 years. Figures taken from the wild involving back calculations ( recapture data from tagged females) suggests 12 to 30 years before maturity. The main differenece probably depend upon latitude and available food.

Courtship and Mating:

Unlike most other species of Sea Turtle, courtship and mating is not performed near the nesting beaches but during migration from the feeding to breeding grounds. Copulation is most accomplished whilst floating but does occur underwater. Several matings make take place and there is evidence that sperm from several males may be stored in the oviducts. All eggs for one season can be fertilised from this stored sperm. Mating normally takes place a few weeks before laying.

n.b. recent observations in Dalyan ( June Haimoff, Conservationist), Turkey and in Kephalonia, Greece suggest that males do move close in shore to mate and even in fresh water lagoons linked to the sea. Reports from Kephalonia even suggest that males seem to set up 'mating' areas which might further suggest some selection process? ( Kephalonia Marine Turtle Project - Tom Stringell)

Sex determination:

Incubation occurs between 26-32 degrees c. Evidence that sex determination is temperature dependent.

Male-biased in the cool. Key or pivotal temperature in which sex ratio is 1:1 is 30 degrees c for the Loggerheads. There is some evidence that this key temperature varies from location to location.

Hatching:

Hatchlings emerge at night, the peak time between 21:00 and 02:00 hours. On cool cloudy days this time will be much later. Together, the hatchlings dig their way out of the nest. Usually emerging at night, the group makes its way down the beach and enters the sea. This race to the sea is important for the hatchlings' biological cycle.

Egg mortality and predation:

In some locations, predation on eggs can be extremely high as shown by work carried out on Dalyan Beach in Turkey (Erk'akan (1991). Out of an estimated 17,254 eggs laid, 12,078 and 1,725 were predated by foxes and ghost crabs respectively. (some of the ghost crab predation was on recent hatchlings.) This predation rate is estimated as high as 70%. On the Northern shores of Cyprus, predation rates are much lower - 38% predated, 8% hatched and predated and 31% unknown (Broderick 1995)

Interestingly, Loggerhead turtles are more prown to predation than Green turtles because their eggs are located nearer the surface.

Hatchling mortality and predation:

Lights near the beach disorientate them, causing the hatchlings to wander in the wrong direction. If this happens, they will die of dehydration or be eaten by predators. The highest mortality occurs at this stage. This migration to the sea is made more difficult by vehicle tracks and sand pits made during the day by tourists. They are too small to climb out and soon die of dehydration in the hot sun of the morning. Many eggs are destroyed by natural activities such as erosion or sea overwash although many eggs are destroyed in the nest by bacteria, fungi and other predators such as racoons (Florida 40-50% are destroyed by racoons, skunks etc). In Zakynthos, Greece, there has been some damage caused by plant roots entering nests and from other females damaging nests on high density laying beaches such as Sekania. Mortality varies greatly from site to site.

Little is known about predation on juveniles and adults but they are generally too,large and well armoured for most predators. Big carnivores like sharks do take turtles. Adults when attacked, present their flanks to the predator and prevent biting.
There have been few quantitative stomach content studies on most sharks although qualitative studies have shown that turtle parts are common in big sharks such as the tiger. One recent study showed a link between the increase in viral infections of sea turtles and the decline in shark numbers: there is speculation that sharks predate on sick turtles? Unfortunately, in Hawaii, where tigers seem to be on the increase, turtle infection is high.(email on the CTURTLE network Oct 1996 Robins J)

Monk seals in Greece are also predators of loggerhead turtles, although the numbers they kill are small (Margaritoulis.D, 1995).

Hatchlings swimming out to sea - the Lost Years

Commensals and disease:

Loggerheads carry more epibiontic animals than the other species of Sea Turtle. There is one barnacle which is specific to the loggerhead:
- see the picture below.

Barnacle on carapace - 35 mm across

Recent work has suggested that barnacles can cause harm to the turtle and there is a possible correlation between the health of the turtle and the number of barnacles it carries on its carapace. ( email via the CTURTLE network Beasley J, sept. 1996) Leeches can cause skin damage and secondary infection (this may cause the tissue to degenerate which is then known as a papillomae).

The most important recent disease of sea turtles, especially Greens, is a disorder known as fibropapillomatosis. The disease is characterised by one or more fibrous tumours, which are located on areas of soft skin. The tumours are debilitating and can prove fatal. The cause is unknown but a viral infection is suspected. Research is underway in a number of Universities. The disease is becoming more common.

Feeding:

Feeding changes with age but loggerheads are mainly carnivorous. Loggerheads will eat almost anything and show little real food preferences. They have powerful jaws and can deal with many food typres. Their diet has been shown to include:

Jellyfish

Crustaceans ( lobsters, crabs and shrimps)

Molloscs ( clams, mussels, conchs etc)

Encrusting animals attached to reefs and rocks

Some stomach content analysis has revealed weed and even plastic bags mistaken for jelly-fish. Oil droplets have also been found in the stomachs of hatchlings which have possibly been confused as potential food particles. (Wietrich, B. 1994)

Threats to survival:

The threats to Loggerheads vary from region to region, although four key areas can be identified.

1. Loss of habitat -

due to commercialisation, including tourism and idustrialisation.

2. Accidental capture by fishing activities -

due to long line fishing and shrimping

3. Pollution -

due to industrial effluent, plastics etc.

4. Human predation -

due to egg collecting.

Meat eating: low due to low palatability of the meat

Turtle-shell: low as poor quality