Turtles in trouble
Marine turtles have been swimming our oceans for at least 110 million years, but now man’s activities threaten turtle populations all over the world. The seven species of marine turtle that swim our oceans are all included on the International Union for the Conservation of Nature’s (IUCN) Red List of Endangered Species.
Entanglement in fishing gear
All species of turtle are susceptible to accidental capture in fishing gear, a phenomenon known as bycatch, throughout the world’s oceans. Turtles become entangled in artisanal gill nets and fish traps set inshore close to the nesting beaches. On the high seas they get caught in massive drift nets, or hooked on pelagic longlines set for tuna and swordfish. At their inshore foraging grounds they are caught by trawlers and gill nets, or entangled in the buoy ropes of static gear such as prawn creels, tangle nets and lobster pots.
Longline fisheries appear to be particularly damaging, and a recent study estimated that more than 50,000 leatherback turtles and 200,000 loggerhead turtles were taken as longline bycatch throughout the world’s oceans in the year 2000 alone.
Use of turtle eggs, meat and shells
Throughout their range, marine turtles are still hunted for their eggs, meat and shells. For example, marine turtles are still legally harvested for their meat in four of the five UK Overseas Territories in the Caribbean, where green and hawksbill turtles are particularly targeted, although the fisheries generally receive little management. It is not known if these harvests are sustainable, but marine turtle nesting populations in these Territories are critically low, probably as a result of historical harvest.
In the tropics, wherever turtles lay their eggs there is a demand for them. In several Caribbean countries, raw turtle eggs are mixed with alcohol and drunk as an aphrodisiac. In Sri Lanka illegal turtle egg collection can result in the removal of 100% of the nests on some unprotected beaches. The eggs are eaten as a cure for asthma, and in Costa Rica they are eaten as an aphrodisiac, although there is no scientific evidence that turtle eggs have any of these properties. Extensive turtle egg collection is thought to have been a significant factor in the decline of several marine turtle populations around the world, including all of Sri Lanka’s turtle nesting populations, and the leatherback nesting population in Malaysia.
In many parts of the world, hawksbill turtles are targeted for the scales (known as scutes) on their shells, which are used to make tortoiseshell. International trade in wild turtle products is banned by all the countries that have signed up to the Convention on International Trade in Endangered Species (CITES), which includes the UK. It is therefore illegal to bring wild marine turtle products into the UK. Yet despite these restrictions, between 1999 and 2004 HM Revenue & Customs seized marine turtle shells, stuffed turtles, tortoiseshell jewelry, turtle oil, meat and eggs, as well as live hatchling loggerhead turtles from travellers entering the UK from the following countries: Antigua & Barbuda, Australia, Bahamas, Barbados, Brazil, Brunei, Cayman Islands, Cuba, El Salvador, Gambia, Ghana, Grenada, Indonesia, Israel, Madagascar, Malawi, Malaysia, Morocco, Mozambique, Nigeria, Seychelles, Sierra Leone, Slovak Republic, Spain, Tanzania, Trinidad & Tobago, Tunisia, USA and Zambia.
Marine turtles depend on a variety of habitats at sea, as well as the all-important nesting beaches. Sadly, these same beaches are under pressure from development, especially from the tourism industry.
If beach development is carried out insensitively it can lead to erosion of sand from the beach, as well as the disturbance of nesting female turtles through increased activity and light pollution.
Light pollution also disorientates emerging hatchlings, making them head inland to artificial light sources rather than out to sea. There are things you can do to be more turtle-friendly when on holiday - to find out more watch our cartoon, Turtles in Trouble.
Predicted sea-level rise resulting from climate change will lead to the inland movement of beaches, a process known as coastal squeeze. Vital turtle nesting habitat could be lost, if nesting beaches are prevented from moving inland by any development or beach armouring behind them.
Marine habitat can also be disturbed or destroyed by development and other human activities. For example, sea grass beds and coral reefs are particularly vulnerable to degradation if exposed to untreated sewage effluent discharged into the sea, and can also be damaged by heavy boat traffic and extensive use by bathers, snorkelers and divers. Excessive and unmanaged boat traffic using key turtle habitat can also lead to fatal boat strike, which has become a significant source of mortality for turtles using coastal waters, for example along the USA’s eastern seaboard.
Marine pollution affects marine turtles and their habitat. Chemical pollution, such as oil spills, can directly affect marine turtles if they are exposed to high levels of pollution, and can lead to contamination of foraging habitat and nesting beaches. Various types of foraging habitat can be degraded, as described above, by exposure to pollution such as untreated sewage effluent.
Turtles can also be killed by entanglement in and ingestion of marine litter, such as discarded fishing gear, plastic bags and balloons. Turtle species such as leatherbacks and juvenile loggerheads, that feed on floating animals such as jellyfish, are particularly vulnerable as they will also attempt to swallow floating litter. Turtles cannot digest plastic and if they eat enough to block their digestive tract they will die from starvation.
Marine litter can also impact on nesting beaches, where accumulations of marine litter through the sand column and on the sand surface can reduce the availability of suitable nesting habitat. Litter on the nesting beach can also be hazardous to nesting females and emerging hatchlings.
Climate change will affect marine turtle populations in several ways. For example, turtle nesting beaches could be inundated if they are prevented from moving inland as a result of sea-level rise; foraging habitat such as tropical coral reefs and sea grass beds could die off as a result of sea-level rise, water temperature rise and the effects of increased storminess and rainfall.
In addition, the sex of marine turtles is determined by the temperature at which the eggs are incubated, with hotter temperatures producing female hatchlings and cooler temperatures producing males. If marine turtles do not change their nesting seasons, then increased surface temperatures at the nesting beaches resulting from climate change could lead to increased production of female hatchlings, and thereby affect natural sex ratios and reproduction.
If we don’t act now to change the way we treat marine turtles and their habitat we may lose some populations forever.
Actions you can take
Did you know?…
Plastic has been found in the stomachs of almost all marine species including fish, birds, whales, dolphins, seals and turtles
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