Threats to Sea Turtles

Hawksbill turtle missing a front flipper swimming Baa Atoll Maldives

A Hawksbill turtle missing a front flipper,
Baa Atoll, Maldives. © Chiara Fumagalli

Sea turtles have been around for millions of years and grace the waters of all the world’s oceans except the Arctic. Unfortunately sea turtles face many threats to their survival and all seven species are listed as endangered by CITES (Convention of International Trade in Endangered Species of Wild Flora and Fauna); six of the seven species of sea turtles are classified as threatened with extinction by the IUCN Red List of Threatened Species (International Union for Conservation of Nature and Natural Resources). One species, the Flatback, is not listed due to insufficient data.

 

 

 

 

 

 

Natural Threats to Sea Turtles

vultures pray on olive ridley turtle eggs Orissa India

Vultures pray on Olive Ridley turtle eggs as a female nests on a beach in Orissa, India. © Emma Doyle

Adult turtles have few natural predators due to their size and hard shells: only sharks, crocodiles, large fish, and occasionally octopus, will attack an adult turtle.

Turtle eggs and hatchlings are the most at risk from natural predators; on the beach and on the way to the water, crabs, birds, and mammals prey on the young turtles and eggs. Once they are in the water, hatchlings and juveniles fall victim to many species of fish.

 

 

 

 

 

Anthropogenic Threats to Sea Turtles

Plove Rideley turtle with fractured shell Michoacan Mexico

An Olive Ridley turtle with a fractured shell arrives to nest on a beach in Michoacan, Mexico. © Enrique Perez

The main threat to sea turtles is, of course, humans and human activity: all species of sea turtles are hunted for their flesh or for their beautiful carapace (especially the Hawksbill, whose shell is known as tortoiseshell). Eggs are also commonly eaten. Turtle oil may be used in cosmetics, while their skin is used as leather.

Though turtles are legally protected in most countries, hunting turtles for meat still occurs around the world. A lack of enforcement, punishment, and public awareness are particularly problematic. The World Health Organization recently advised against eating sea turtle flesh as it may contain Salmonella bacteria, mycobacteria, Leptospires, other bacteria, parasites, trematodes, or high levels of heavy metals and pesticides such as DDT.

Turtles can hold their breath for long periods of time, but they do have to surface to breath at regular intervals. Whilst on the surface they are vulnerable to be hit by boats and other water crafts. Injuries and death caused by boat strikes have become quite common.

 

 

By-catch in Fisheries
turtles caught as bycatch

Turtles caught as by-catch
©Projeto Tamar Brazil/Marine Photobank

Accidental capture in fishing nets (also known as by-catch) is a major threat to marine life worldwide. Every year hundreds of thousands of turtles are captured, injured, or killed in gill-nets, trawl-nets and on longline hooks. The fate of injured turtles caught and released remains unknown.

Gill-nets are the dominant gear in the Indian Ocean. Gill-nets are used in artisanal and semi-industrial fisheries, contributing to 30-40% of the total catch. The rate of by-catch, particularly for sharks and turtles, is high.

Trawling, which involves dragging a fishing net behind a boat, is a common fishing technique in India and Sri Lanka. By-catch is extremely high and nets are often lost due to snagging on the bottom.

The Maldives’ pole-and-line tuna fishery is one of the most sustainable fisheries in the world: it is very species-specific and has a low rate of by-catch.

 

 

 

 

Ingestion of Marine Debris
plastic floating in the ocean Maldives

Plastic floating in the ocean can easily be mistaken for jellyfish – a favourite food for turtles.
© Jannicke C Hallum

Currently, it is estimated that there are 100 million tons of plastic in the ocean, which is responsible for killing ~100 million marine animals every year.

Sea turtles often mistake plastic bags for jellyfish, one of their prey items. Young turtles usually rely on oceanic currents to feed because they concentrate seaweed; however, oceanic gyres also concentrate garbage and pollutants, such as oil and tar balls, which are eaten by young turtles and other animals.

 

 

 

 

 

 

 

Entanglement in Ghost Nets
3 turtles trapped in a ghost net

3 turtles are trapped in a ghost net, Maldives
© Dave Bretherton

Ghost gear (lost, abandoned, or discarded fishing nets and other gear) poses a serious threat to sea turtles and other marine animals around the world. Every year, countless turtles approach these ghost nets looking for food or shelter and become entangled in them.

The ghost nets cut into their flippers or neck, cause exhaustion, starvation, dehydration, and eventually result in a slow and painful death. The problem of ghost fishing is not yet well quantified or understood. See section xx for more information on the problem of ghost fishing.

 

 

 

 

Artificial Lighting on Nesting Beaches
nesting green turtle makes her way arouond beach furniture Maldives

A nesting Green turtle makes her way around some beach furniture at a resort in the Maldives. © Chiara Fumagalli

Nesting turtles must now compete with tourists and coastal residents for the use of beaches. Artificial lights on nesting beaches cause confusion and disorientation of female turtles and hatchlings, which normally navigate towards sea by the reflection of the moon on the water. Turtles may accidentally head inland and be killed on roads, by predators, or die of dehydration and exhaustion.

Night-time human activity can prevent mothers from emerging on the beach or cause them to stop mid-nesting. Beach furniture creates obstacles and turtles may even become stuck in them.

 

 

 

 

Erosion and Beach Armouring
seawall Maafushi harbour Maldives

Seawall protecting the harbour of Maafushi Island, Maldives © Jannicke C Hallum

The development of coastal areas often results in erosion, leaving little space for nesting turtles. On eroded beaches, turtles may nest below the high tide line, resulting in flooding of the nest.

Man-made structure such as sea walls and sandbags used to protect coastal properties from natural erosion reduce nesting habitats and displace turtles from optimal nesting areas.

 

 

 

 

Major Threats to Turtles in the Indian Ocean

Currently, the biggest threats to turtles in the Indian Ocean are direct harvest for meat and eggs, the pet trade (hatchlings), marine garbage (including ghost nets), and the destruction of nesting habitats.

The fisheries in the Maldives pose little threat to turtles, as the primary method of fishing is live bait pole-and-line; however, fishing techniques used elsewhere in the Indian Ocean including gillnetting, trawling, long lining, and purse seine fishing associated with fish aggregating devices (FADs) all pose serious threats to sea turtles both as active fishing techniques and in the ghost gear that they generate.

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