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Together we can ensure a better future for turtles and help keep our oceans healthy.

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Turtles are among the most ancient animals to inhabit our planet. But they are facing serious threats to their existence. For species that survived the last global extinction event which killed the dinosaurs[1], it is tragic to see the effects of the current sixth mass extinction[2], the only one to be precipitated by human activity, on turtle numbers. Six out of the world’s seven sea turtle species are now classified by the IUCN as Vulnerable, Endangered or Critically Endangered globally[3]:

VULNERABLE: loggerhead (Caretta caretta), leatherback (Dermochelys coriacea), olive ridley (Lepidochelys olivacea);

ENDANGERED: green sea turtle (Chelonia mydas);

CRITICALLY ENDANGERED: hawksbill (Eretmochelys imbricata), Kemp’s ridley (Lepidochelys kempii).

There is currently not enough data available for the flatback turtle (Natator depressus) to assess its conservation status.

What threats do sea turtles face?‍

The sea turtles that we see coming into rescue centres, primarily in the Mediterranean, have often become entangled in discarded fishing nets or other rubbish, or swallowed a fishing hook and line, been hit by a boat propellor, or suffered deliberate injury by fishermen who sometimes view them as competition for their catch. Perhaps most worryingly of all it is now more likely than not that a sick or injured turtle will have ingested plastic waste or other anthropogenic rubbish[4],even if that isn’t the primary reason that they find themselves in a rescue centre.

Entanglement‍

Getting caught up in abandoned fishing equipment, or ‘ghost gear’, or other rubbish – like plastic six-pack rings – is a major threat to turtles. Discarded fishing gear is responsible for the majority of entanglements, with hundreds of tonnes being lost or abandoned every year, but other plastic rubbish can also have devastating consequences. Apart from six-pack rings, turtles have been found trapped in plastic sacks, twine, polythene sheeting, plastic chairs and plastic packaging straps[5].

Until the 1950s, the fishing industry tended to use natural fibres, like cotton, jute and hemp, but the demand for more resistant materials saw these increasingly replaced by nylon, polyethylene and polypropylene.‘Ghost’ fishing nets are now usually made of non-biodegradable material like nylon and can be several kilometres long. As they drift through the ocean they accumulate marine organisms in a process known as ‘bio-fouling’ and consequently attract a range of grazers and predators who can then become trapped. Studies suggest that turtles are particularly vulnerable to this fate[6]. Entanglement can have a range of consequences for turtles, from abrasions, serious wounds, infection and loss of flippers, to the restriction of shell growth, choking and drowning.

Turtles can of course also find themselves unintended bycatch in active fishing nets too. Decompression sickness is a real risk if a turtle is accidentally pulled up to the surface too quickly and helping rehabilitators and rescue centres quickly recognise and treat affected animals is key to their survival.

Fishing hooks and lines

Turtles often accidentally swallow fishing hooks. Fortunately, for those turtles lucky enough to find themselves taken to a rescue centre as a result, it is often possible to carefully remove the hook under anaesthesia. However, some of the saddest cases our veterinary team see are those where the turtle has swallowed both hook and line, and the hook has become embedded in the oesophagus but the line has passed through the gut and is protruding from the cloaca. The risk of the intestinal wall being irreparably damaged by the fishing line is high, although some animals are lucky and with careful intervention and good care do make a full recovery.

Boat strikes and head injuries

Tourist boats and others often do not take enough care, failing to maintain a safe distance, speed and density when travelling through waters where turtles are present. The result is all to often injury to the carapace or other parts of the body. An additional problem seen by our colleagues at the ARCHELON rescue centre in Greece is deliberate injury to the head by fishermen, a minority of whom persist in viewing turtles as competition for valuable catch. Some of the resultant head wounds are horrific, with exposed brain tissue. However, correct wound management, in conjunction with good nutrition and overall husbandry, often means a turtle can make a good recovery and eventually return to the sea.

Plastic ingestion

Direct ingestion of plastic is now very common and has been documented in all seven species[7]. Worldwide, it’s estimated that we are tipping the equivalent of one overflowing bin lorry load of plastic into the oceans every three minutes.[8] According to another estimate, there are five trillion pieces of plastic in the surface waters of our planet’s seas[9]. Plastic waste is found throughout oceanic water columns and on the seabed too. It should come as little surprise, therefore, that mistaking plastic waste for food is a very real risk for sea turtles and research now suggests that ingesting 14 pieces of plastic results in a 50% chance of a turtle dying[10].

Turtles are primarily visual feeders and it is not unusual for plastic bags, balloons and sheeting to be confused with prey like jellyfish and actively selected and consumed. However, there is now evidence that turtles may also be reacting to the smell of biofouled plastic, which has been colonised by microbes, algae and small animals, in exactly the same way as they respond to their real food[11].

In addition to the potential damage from ingested fishing line, other macro plastics consumed by turtles can cause intestinal blockages, leading to constipation and the accumulation of hardened faeces. The chronic effects of plastic ingestion may not present themselves until long after the initial consumption of rubbish, but the resultant reduction in stomach capacity and normal feeding stimuli can lead to malnutrition, and, particularly in young turtles, starvation.

Young turtles tend to swim in areas of the ocean particularly likely to accumulate plastic waste (as a result of advection currents), making them especially vulnerable. Their small size may put them atgreater risk of mortality from plastic ingestion, thanks to their less robust and smaller digestive tracts. One study in 2015 found that just 0.5g of debris, made up predominantly of soft plastics and fibres, was enough to block the digestive tract of a juvenile green turtle, resulting in the animal’s death[12]. Another revealed that four out of five post hatchling flatback turtles had ingested fragments of plastic[13]. Experimental evidence from post-hatchling loggerhead turtles has shown that where the turtles’ natural diet is disrupted – for example because their stomachs contain plastic – they have reduced energy, may have difficulty obtaining enough nutrients for growth and can starve more quickly due to their smaller size[14].

Ingested plastic can also affect a turtle’s buoyancy and ability to swim, as many plastics are less dense than water and large amounts in the gut can impact the turtle’s ability to control its buoyancy. This is particularly serious for deep-diving turtles like leatherbacks[15]. And it has even been known to affect the ability of a female leatherback to lay her eggs, due to plastic blocking her cloaca[16].

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Turtles, Humans & Microplastics.

The issue of indirect ingestion of microplastics deserves special attention, not least because of the obvious implications for people, given that we now know how ubiquitous they are in our own water supplies and beyond. We will look at this in more detail in our next news article.

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Nesting Beaches

Although less directly related to the health and veterinary aspects of turtle conservation, the over-development of nesting beaches, the prevalence of plastic waste, theft of eggs and the impacts of climate change, where higher temperatures mean a disproportionate number of hatchlings will be female, also pose very real threats to sea turtles.

[1] https://www.nbcnews.com/id/wbna43716148#:~:text=The%20tough%20turtles%20of%20the,aquatic%20lifestyles%2C%20researchers%20now%20say.

[2] https://www.worldwildlife.org/stories/what-is-the-sixth-mass-extinction-and-what-can-we-do-about-it#:~:text=The%20planet%20has%20experienced%20five,of%20a%20sixth%20mass%20extinction.

[3] https://www.iucn-mtsg.org/statuses

[4] https://www.eurekalert.org/news-releases/556004

[5]Duncan, E. et al.(2017) A global review of marine turtle entanglement in anthropogenic debris: abaseline for

furtheraction. Endangered Species Research, Vol. 34: 431-448: p436

[6] Nelms, S., Duncan,E., et al. (2016) ICES Journal of Marine Science, Vol. 73(2): 165-181

Plasticand marine turtles: a review and call for research. ICES Journal of MarineScience, Vol. 73(2): 165-181; p173

[7]Nelms, S., Duncan,E., et al. (2016) ICES Journal of Marine Science, Vol. 73(2): 165-181

Plasticand marine turtles: a review and call for research. ICES Journal of MarineScience, Vol. 73(2): 165-181; p166

[8] https://www.youtube.com/watch?v=2zrh-_pv_oY

[9]Duncan, E, et al.(2019) Microplastic ingestion ubiquitous in marine turtles. Global ChangeBiology, Vol. 25, 744-752

(2019);p744

[10] https://www.nature.com/articles/s41598-018-30038-z

[11] https://www.cell.com/current-biology/pdf/S0960-9822(20)30115-9.pdf

[12] Nelms,S., Duncan, E., et al. (2016) ICES Journal of Marine Science, Vol. 73(2):165-181

Plasticand marine turtles: a review and call for research. ICES Journal of MarineScience, Vol. 73(2): 165-181; p172

[13] Nelms,S., Duncan, E., et al. (2016) ICES Journal of Marine Science, Vol. 73(2):165-181

Plasticand marine turtles: a review and call for research. ICES Journal of MarineScience, Vol. 73(2): 165-181; p172

[14] Nelms,S., Duncan, E., et al. (2016) ICES Journal of Marine Science, Vol. 73(2):165-181

Plasticand marine turtles: a review and call for research. ICES Journal of MarineScience, Vol. 73(2): 165-181; p172

[15] Duncan,E. et al. (2017) A global review of marine turtle entanglement in anthropogenicdebris: a baseline for

furtheraction. Endangered Species Research, Vol. 34: 431-448: p439

[16] Nelms,S., Duncan, E., et al. (2016) ICES Journal of Marine Science, Vol. 73(2):165-181

Plasticand marine turtles: a review and call for research. ICES Journal of MarineScience, Vol. 73(2): 165-181; p172

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