Credit: Pixabay.

Scientists estimate that more than half of all sea turtles have eaten plastic debris in some proportion. The rubbish, which was once in the hand of a human before it made its way into the world’s oceans, comes in all shapes and sizes, from microscopic pebbles to jellyfish-like undulating plastic bags.

A recently published study cataloged the damage done to sea turtles by plastic pollution. The findings suggest that just 14 pieces of plastic are enough to significantly increase the animals’ risk of death. If an animal had ingested more than 200 pieces of plastic, death was inevitable. In some cases, a single piece of plastic was deadly.

The international team of researchers wanted to investigate the inflection point where the ingested plastic reaches a lethal level. To this aim, they examined the necropsies of 246 sea turtles, as well as 706 records from a national stranding database relating to sea turtles in Queensland, Australia.

The researchers found that the animals that died for reasons unrelated to eating plastic had less plastic in their gut than sea turtles that died of unknown causes or direct ingestion of plastic.

The most vulnerable group are juveniles — half of which are expected to die if they ingest 17 pieces of plastic of more. A sea turtle typically lives to be 80 years old but a juvenile, which is too young to reproduce, can range from 20 to 30 years of age. The authors estimate that 90% of juvenile green sea turtles off the coast of Brazil have ingested plastic.

“Young small turtles actually drift and float with the ocean currents as does much of the buoyant, small lightweight plastic,” Dr. Britta Denise Hardesty from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), told BBC News.

“We think that small turtles are less selective in what they eat than large adults who eat sea grass and crustaceans, the young turtles are out in the oceanic area offshore and the older animals are feeding in closer to shore.”

It’s difficult to pin the cause of death of a turtle to plastic except for in cases where the damage is self-evident. However, the work quantifies the toll of plastic pollution on sea turtle health and provides a measurable yardstick for future research.

In one case, researchers found as many as 329 pieces of plastic in the gut of a sea turtle. On the opposite end, a deceased turtle was found with its digestive tract blocked by a single item — a soft piece of plastic. In another turtle, its intestines were perforated by a sharp plastic debris.

The authors of the study write that even though plastic might not kill all turtles, its presence will certainly weaken the animals by impending their normal digestion.

The next step in the research is to establish whether plastic pollution in the oceans is causing a population decline. In some places, the problem is worse than in others. For instance, the Mediterranean and the southern Atlantic Ocean are so riddled with debris that it’s almost impossible for turtles to avoid the debris.

More research will hopefully paint a clearer picture of the damage — done not just to sea turtles, but other animals as well. Previously, a study found plastic debris in the guts of 90% of seabirds.

The authors say that it’s possible to reduce plastic exposure by banning certain high-impact items, such as straws or coffee pods. 

The findings appeared in the journal Scientific Reports.