A new study shows that especially for young turtles, ingesting just a little more than a dozen pieces of plastic in the ocean can be lethal.
Plastics removed from the intestine of a sea turtle. The study found that half of juvenile turtles would be expected to die if they ingested 17 plastic items. Credit Kathy Townsend
All over the world, sea turtles are swallowing bits of plastic floating in the ocean, mistaking them for tasty jellyfish, or just unable to avoid the debris that surrounds them.
Now, a new study out of Australia is trying to catalog the damage.
While some sea turtles have been found to have swallowed hundreds of bits of plastic, just 14 pieces significantly increases their risk of death, according to the study, published Thursday in Scientific Reports.
Young sea turtles are most vulnerable, the study found, because they drift with currents where the floating debris also accumulate, and because they are less choosy than adults about what they will eat.
Worldwide, more than half of all sea turtles from all seven species have eaten plastic debris, estimated Britta Denise Hardesty, the paper’s senior author and a principal research scientist with the Commonwealth Scientific and Industrial Research Organization in Tasmania. “It doesn’t matter where you are, you will find plastic,” she said.
Six of the seven species of sea turtles are considered threatened, although many populations are recovering.
The study examined data from two sets of Australian sea turtles: necropsies of 246 animals and 706 records from a national strandings database. Both showed animals that died for reasons unrelated to eating plastic had less plastic in their guts than those that died of unknown causes or direct ingestion.
But the deaths are hard to pin down. “Just because a turtle has a plastic in it, you can’t say that it died from it, except in very extenuating circumstances,” Dr. Hardesty said. Even a single piece of plastic can occasionally cause death. In one case a turtle was found with its digestive tract blocked by a soft piece of plastic; in another, its intestine was perforated by a sharp piece of plastic.
In others, a variety of plastic material was found inside their digestive tracts — as many as 329 pieces in one sea turtle. Because of their anatomy, sea turtles cannot vomit up something once they’ve swallowed it, Dr. Hardesty said, meaning it either passes through their gut or gets stuck.
For a juvenile of typical size, half the animals would be expected to die if they ingested 17 plastic items, the study concluded. Sea turtles can live to be 80 or more years old, Dr. Hardesty said, with juveniles too young to reproduce ranging up to age 20 to 30.
The study’s innovation was to try to determine this inflection point, where the load of plastic becomes lethal, said T. Todd Jones, a supervisory research biologist with the National Oceanic and Atmospheric Administration in Hawaii.
“There’s always been this question of when is plastic too much?” Dr. Jones said.
An animal that swallows a lot of plastic might appear healthy, Dr. Jones said, but might be weakened by plastic in its gut limiting food absorption…