Rising amounts of plastic pollution in the Pacific Ocean have created an “evolutionary trap” for turtles as they spend their juvenile years in some of the worst-affected waters, scientists say.
Researchers from Exeter University found plastic inside young turtles along the Pacific and Indian Ocean coasts of Australia. After hatching on beaches the creatures spend years travelling on ocean currents.
Emily Duncan, of the Centre for Ecology and Conservation on the university’s Penryn campus in Cornwall, said that juvenile turtles had evolved to grow in the ocean, where predators were relatively scarce. “Our results suggest that this evolved behaviour now leads them into a ‘trap’, bringing them into highly polluted areas,” she said.
Juvenile sea turtles generally have no specialised diet. “They eat anything,” Duncan said. “Our study suggests this includes plastic. We don’t yet know what impact ingesting plastic has on juvenile turtles but any losses at these early stages of life could have a significant impact on population levels.”
The turtles swim into the waters between California and Hawaii, referred to as the Great Pacific Garbage Patch. Almost 90,000 tonnes of rubbish cover an area more than twice the size of Texas. The Ocean Cleanup, a non-profit organisation, says that it is one of five “plastic accumulation zones” in the world. Scientists say that up to nine million tonnes of plastic enter the seas each year.
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An “evolutionary trap” occurs when a behaviour that has developed over many generations comes to have negative effects on overall survival.
The Exeter researchers examined juvenile sea turtles that had either washed up or were accidentally caught during fishing off Australia.
The study included 121 sea turtles from five of the seven species: green, loggerhead, hawksbill, olive ridley and flatback. The proportion of turtles containing plastic was considerably higher on the Pacific coast.
The journal Frontiers in Marine Science reported yesterday that 86 per cent of loggerheads from the Pacific had consumed plastic, compared with 21 per cent from the Indian Ocean. One turtle in the Indian Ocean contained 343 pieces of plastic.
The material in the Pacific turtles consisted mostly of hard fragments while Indian Ocean plastics were mostly fibres, possibly from fishing ropes or nets. The polymers most commonly ingested by turtles in both oceans were polyethylene and polypropylene.
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“Hatchlings generally contained fragments up to about 5mm to 10mm in length and particle sizes went up along with the size of the turtles,” Duncan said. “The next stage of our research is to find out if and how plastic ingestion affects the health and survival of these turtles. This will require close collaboration around the world.”
