AUSTRALIAN BIODIVERSITY RECORD - Calodema

Australian Biodiversity Record, 2007 (7): 1-90Most workers treat this as a single variable species, although it is often divided into twoseparate subspecies - Eretmochelys imbricata imbricata (Linnaeus, 1766), from the AtlanticOcean, and Eretmochelys imbricata bissa (Rüppell, 1835), for the Pacific and Indian Oceans‘population’; some workers regard this latter population as being referrable to Eretmochelysimbricata squamata Agassiz, 1857 but I consider this to be in error.Description: To many people, this is the most beautiful of the sea turtles. The base colour ofthe carapace may be greenish to dark chocolate brown, with delicate flecks of golden yellow,and prominent black or reddish variegations which radiate across the scutes. The sutures ofthe head and limbs are edged in white, and the plastron is almost immaculate white. Thehatchlings are usually blackish above and dark brown below. Proportionally to other turtles,this species has quite a small head. However, the snout protrudes somewhat forming aparrot-like beak, hence its common name of Hawksbill Turtle. The head has 2 pairs ofprefrontals. The carapace is heart-shaped, the dorsal scutes tend to be raised somewhat,overlapping one another in mature specimens, and the margin of the shell has a slightlyserrated appearance. There are 4 pairs of costal shields It reaches a maximum size of onlyabout 1 m, and is often slightly smaller at about 800mm shell length.Distribution: Hawksbill Turtles are found throughout the tropical and warm temperate watersof the world. In Australia, they mainly occur along our tropical coasts. They are mainly foundin continental waters from about Fraser Island in Queensland, up the virtually the entire coastto Torres Strait, through the Gulf of Carpentaria, along the entire coast of the NorthernTerritory, and in coastal waters of Western Australia, to about as far south as Carnarvon. Thisspecies is rarely known to breed in Australia, and then mainly on sandy islands around theGulf of Carpentaria and Torres Strait, but it has also been rarely recorded breeding as farsouth as Brisbane in Queensland. Also vagrants may reach the waters of New South Wales,Victoria or even Tasmania.Habitat: They prefer the shallower rocky continental shelf waters of our northern and easterncoasts and are often found closely associated with islands and coral reefs, such as the GreatBarrier Reef where they forage around the shallows.Biology/Ecology: It is known that in some parts of the species' distribution, this species canmigrate vast distances between feeding and breeding areas. However, in Australia, breedingand feeding areas are within close proximity of one another and migratory behaviour is lesspronounced than elsewhere in the world. Females can breed over most of the year, butSummer is the peak of reproductive activity. Up to four clutches (each laying separated by 2-3weeks) may be produced by a single female in a season. Usually females produce only about50 small round eggs at a laying, but sometimes clutches may exceed 100 eggs. Sometimeslarge clutches may be separated by a few years due to the energy demands that such areproductive effort places upon a female. The eggs hatch after about 50-60 days incubation.Nesting occurs about every 3 years. Although generally regarded as an omnivorous species,this is mainly a carnivorous species, feeding largely on fish, molluscs, sponges, ascidians,anemones, jelly-blubbers and crustaceans. Marine algae is also eaten. Juveniles andimmature specimens are entirely carnivorous. Many species that this turtle feeds upon havetoxins present in their tissues, and this has resulted in Hawksbill Turtles being quitehazardous as a human food source.Toxicity: The meat, adipose tissue, organs, blood, and eggs of Hawksbill Turtles areconsumed by humans in various parts of the world (including traditional hunters in northernAustralia) and it is known that many deleterious health consequences may also result fromtheir consumption. Among the identified health hazards of sea turtle products are bacterialand parasitic infections which have led to extreme illness or even death by organ damage,diarrhoea, vomiting, and extreme dehydration. A range of identified biotoxins andenvironmental contaminants such as heavy metals and organochlorine compounds, have alsobeen detected that are above WHO safety levels. In some parts of the world this species nowconsumes less of some of the more toxic sponge species due to ecological changes to theirenvironment. This has resulted in the natural toxicity of Hawksbill Turtle meat apparentlydeclining between the 17th and 20th centuries. Consuming contaminated sea turtle productshowever, may lead to neurotoxicity, kidney disease, liver cancer, and developmental effects in10