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 on 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 turtle eggs as a female Olive ridley nests on a beach in Orissa, India ©Emma Doyle

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

Turtle eggs and hatchlings, on the other hand, are at great 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. The hawksbill’s carapace, known as tortoiseshell, is particularly in demand. Turtle eggs are commonly eaten, turtle oil is used in cosmetics, and turtle skin is used as leather.

Despite the legal protection of sea turtles in most countries, hunting turtles for meat still occur around the world. A lack of enforcement, punishment, and public awareness is 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.

Sea turtles can hold their breath for long periods of time, but they do have to surface to breathe 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 bycatch
©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, gill-nets, trawl-nets and on longline hooks capture, injure and kill hundreds of thousands of sea turtles. The fate of injured turtles caught and released remains unknown.

Gill-nets are the dominant gear in the Indian Ocean, contributing 30-40% of the total catch for artisanal and semi-industrial fisheries. The rate of bycatch, 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 resembles jellyfish – a favourite food for turtles ©JCHallum

A study published in 2015 estimates that eight million metric tons of plastic waste end up in the ocean every year. Most of the plastic waste consists of everyday items such as bottles, bags, wrappers, balloons, and straws. However, the majority of plastic waste floating in the ocean consists of broken down plastic fragments called microplastic. The same study estimates that there are between 93,000 and 236,000 metric tons of microplastic in the ocean. Marine debris poses a threat to a wide variety of marine animals,  killing more than an estimated 100 million 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 young sea turtles and other animals mistake for food.

The implications of marine debris ingestion include death through the perforation of the digestive system and exposure to chemicals. All six species of sea turtle listed on the IUCN Red List have been documented to ingest debris.

 

Entanglement in Ghost Nets

3 turtles trapped in a ghost net
One ghost net entangles three turtles, 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.

 

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 sea 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. Sea turtles normally navigate towards the sea by the reflection of the moon on the water: Artificial lighting can instead lead them inland to be killed on roads or by predators, or to 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 ©JCHallum

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

Man-made structures 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

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

Since the primary method of fishing in Maldives is live bait pole-and-line, Maldivian fisheries pose little threat to turtles. 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.