Habitat and Biology:

illustration: M. Demma © ICRAM

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 °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. It has been suggested 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. Loggerheads are found all over the Mediterranean although most activity occurs in the Eastern part of the basin 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 most common nesting turtle, with Greece hosting the highest nesting populations of more than 2,000 individuals. 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
  
  

  illustration: M. Demma © ICRAM

  Nesting behaviour:   The female usually come ashore at night (records suggest that this may well have once 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, the turtle 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.

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.

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: 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.

illustration: M. Demma © ICRAM	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.
illustration: M. Demma © ICRAM	Maturity: The age of maturity is not clear but research in captive specimens puts it between 6 and 20 years. Figures taken from the wild involving back calculations (recapture data from tagged females) suggests 12 to 30 years to maturity. The main difference probably depends on latitude and food availability .
illustration: M. Demma © ICRAM	Courtship and Mating: Unlike most other sea turtle species, 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. Observations in Dalyan ( June Haimoff, Conservationist), Turkey and in Kefalonia, Greece suggest that males do move close in shore to mate and even in fresh water lagoons linked to the sea. Reports from Kefalonia suggest that males seem to set up 'mating' areas which might further suggest some selection process (Kefalonia Marine Turtle Project - Tom Stringell)

Sex determination:

• Incubation occurs between 26-32°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°C for the Loggerheads. There is some evidence that this key temperature varies from one location to another.

Hatching:

• Hatchlings emerge at night, with a peak time between 21:00 and 02:00 hours. On cool cloudy days this time-period will be longer. 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. 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) .
• Loggerhead turtles are more prone to predation than Green turtles because their eggs are located closer to the surface of ther beach.

Hatchling mortality and predation:

• Lights near the beach disorientate hatchlings, causing them to wander in the wrong direction. If this happens, they may die of dehydration or are eaten by predators. The highest mortality occurs at this stage. This route to the sea is made more difficult by vehicle tracks and sand pits made during the day by tourists. Hatchlings are too small to climb out of the ruts 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, while others are destroyed in the nest by bacteria and fungi, or predators such as racoons (In Florida, 40-50% of the clutch is destroyed by racoons, skunks etc). In Zakynthos (Greece), there has been some damage caused by plant roots entering nests and from other nesting 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. However, large arnivores like sharks do take turtles. When attacked, adults present their flanks to the predator to 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 shark. One recent study showed a link between the increase in viral infections of sea turtles and the decline in shark numbers.
• 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, pictured below:

• 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. (e-mail 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:

Jellyfish	Molluscs	Crustaceans
Illustrations: M. Demma © ICRAM

• 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 types. Their diet has been shown to include:
  • Jellyfish
  • Crustaceans ( lobsters, crabs and shrimps)
  • Molluscs ( 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).

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