How Much Plastic Does It Take To Kill a Sea Turtle?

A new study suggests one piece of plastic has a 22 percent chance of killing a turtle that eats it, and 14 pieces will kill half

CSIRO/Kathy Townsend, University of Sunshine Coast

A lot of attention has been paid to how ingesting plastic impacts seabirds, fish and sea turtles in recent years. It’s logical to assume that nomming on bits of plastic is detrimental, but researchers weren’t certain just how much plastic was too much or even if the plastic found in some sea turtle stomachs was a direct cause of death. Carla Howarth at the Australian Broadcasting Network reports that a new study on sea turtles tried to figure that out, finding that in some cases, nibbling on just one piece of plastic could kill the animals.

In a new study published in the journal Scientific Reports, scientists examined data about the deaths of 1,000 sea turtles that washed up on the shores of Australia, looking at the amount of plastic debris found inside their stomachs, intestines and rectums. According to a press release, researchers at Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia found that a turtle had a 22 percent chance of dying from ingesting one plastic item. Once a turtle gobbles 14 pieces of plastic, the mortality rate jumps to 50 percent. Once an animal eats 200 pieces of plastic death is eminent, reports Matt McGrath at the BBC.

The researchers estimate that 52 percent of sea turtles across the globe have some plastic in their guts, but plastic ingestion rates are different around the world. In Uruguay for example, Howarth reports 100 percent of turtles sampled had plastic in their intestinal tracts.

Plastics decimated younger turtles, defined as post-hatchling turtles that just started to swim and juvenile turtles the size of a dinner plate or smaller. Researchers found 54 percent of post-hatchling turtles and 23 percent of juvenile turtles had plastic inside of them compared to 16 percent of adult turtles.

“Young small turtles actually drift and float with the ocean currents as does much of the buoyant, small lightweight plastic," lead author Britta Denise Hardesty of CSIRO tells the BBC. “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.”

The physiology of turtles also makes plastic lethal for them since the animals can’t regurgitate, meaning whatever they eat is on a one-way trip through their gut. Even one small piece of plastic that gets trapped in the wrong place can cause a blockage that leads to death.

Not everyone agrees with the study's conclusions. Jennifer Lynch at the National Institute of Standards and Technology in Hawaii has also looked at plastic in turtles, reports Karen Weintraub at The New York Times. But instead of looking at turtles that died and washed up on the beach, she examined healthy animals that were accidentally caught by longline fishermen and drowned. In her study she found animals with over 300 pieces of plastic in them that were relatively healthy. “They ate a lot of plastic but it did them no harm,” Dr. Lynch said of the animals she’s examined. “They swallow it and they poop it out.”

That doesn’t mean the plastic isn’t doing harm, but Lynch thinks there’s more work to be done to understand the physiological effects of the plastic. She also says it’s more useful to look at the weight of the plastic turtles have ingested instead of focusing on the number of pieces, which can vary greatly in size.

In the next step of their research, reports Howarth at ABC, the CSIRO team wants to combine their recent data with other research on the prevalence of plastic ingestion to come up with estimates of how many turtles per year are killed by plastics.

Eating plastic is not the only problem the marine reptiles face. A study last year also showed that fishing line, discarded fishing gear, six-pack rings, strings, ropes and other plastic debris can get tangled up with the turtles, causing them to drown. The solution is, of course, preventing the plastic from getting into the ocean and cleaning up what’s already there. Both of those projects, however, are easier said than done, though at least one controversial project was recently launched to try and tackle part of the problem.

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