Sea turtles are one of the most beautiful and enigmatic creatures found within our seas, however despite this most species are endangered, primarily green turtles (Chelonia mydas), loggerhead turtles (Caretta caretta) and leatherback turtles (Dermochelys coriacea). All of these species are now in danger of becoming extinct due to human impacts on their habitats, life cycle and the focus of this blog, their food sources. Many turtles regularly consume jellyfish, specifically leatherbacks where jellyfish make up a large amount of their diets, and also loggerheads; while others feed on seaweeds and sea grasses in the case of the green turtles, however they are omnivorous when young meaning they will eat just about anything.
The human impact here is our dumping of plastics into the oceans specifically plastic bags, one of the most commonly found plastics anywhere in the world, which unfortunately find their way into the sea more often than not where they pose a serious risk to sea turtles. The above image shows a jellyfish and a plastic bag side by side in water, and you will notice that there is a striking resemblance between the two, and for turtles which primarily distinguish prey items by sight, they may as well be identical. For turtles the ingestion of a plastic bag can prove lethal, with the plastic bags blocking the intestinal tract of the turtles causing starvation or a rupture of the intestines of the turtles, as well as causing the turtles to accumulate gases in their gut which disrupts their buoyancy causing them to float which makes them far more vulnerable to predators.
A study conducted between 1997 and 1998 (L Bugnoi, et al. 2001) showed that of 38 dead green turtles examined 50% of them had plastic bags in their guts and roughly 40% having ingested plastic ropes. This shows that this problem has existed for a very long time and that it was devastating 20 years ago, and that the situation has not improved much in that time. If this is the effect plastic bags have on the vegetarian green turtle, then the effect on the leatherbacks with their diet of almost entirely jellyfish is even more severe.
This goes to show that as simple and as small an item as a plastic bag can have devastating consequences for marine life if it makes its way into the ocean. But things are improving, in October 2015 the 5p charge for plastic bags was introduced in the UKand in the 6 months following plastic bag usage dropped from 7 billion to approximately 500 million, and with some store stopping the sale of plastic bags completely late last year things are improving. So the fix in this case is simpler than most, just stop buying plastic bags, use reusable plastic bags whenever possible, and if you see a plastic bag in the street or on a beach, pick up and put it in a bin.
Carvalho, RH., Lacerda, PD., Mendes, SS., Barbosa, BC., Paschoalini, M., Prezoto, F., Sousa, BM. 2015. Marine debris ingestion by sea turtles (Testudines) on the Brazilian coast: an underestimated threat?. Marine Pollution Bulletin. Page 4.
Bugoni, L., Krause, LG., Petryà, MV. 2001. Marine Debris and Human Impacts on Sea Turtles in Southern Brazil. Marine Pollution Bulletin. Pages 1330-1334.
Schuyler, QA., Wilcox, C., Townsend, K., Hardesty, BD., Marshall, JN. 2014. Mistaken identity? Visual similarities of marine debris to natural prey items of sea turtles. BMC Ecology.
The Guardian. 30th July 2016. England’s plastic bag usage drops 85% since 5p charge introduced. [ONLINE]. [13th Feb 2018]: https://www.theguardian.com/environment/2016/jul/30/england-plastic-bag-usage-drops-85-per-cent-since-5p-charged-introduced
The Guardian. 7th August 2017. Tesco to end sales of 5p carrier bags. [ONLINE]. [13th Feb 2018]: https://www.theguardian.com/environment/2017/aug/07/tesco-to-end-sales-of-5p-carrier-bags
South Pacific Regional Fisheries Management Organisation. What Do Leatherback Sea Turtles Eat. [ONLINE]. [13th Feb 2018]: http://www.southpacificrfmo.org/what-do-leatherback-sea-turtles-eat/