Plastic pollution creating ‘evolutionary trap’ for young sea turtles

A research team led by the University of Exeter has found plastic inside small juvenile turtles along both the east (Pacific Ocean) and west (Indian Ocean) coasts of Australia.

After hatching on beaches, the animals then travel on currents and spend their early years in the open ocean. However, these currents accumulate vast quantities of plastic and because the young turtles primarily feed near the surface, many inadvertently swallow plastic as a result.

The research team also involved scientists from Murdoch University, the Department of Environment and Science (Queensland) and the Department of Biodiversity Conservation and Attractions (Western Australia).

Dr Emily Duncan, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall, said: “Juvenile turtles have evolved to develop in the open ocean, where predators are relatively scarce. However, our results suggest that this evolved behaviour now leads them into a trap, bringing them into highly polluted areas such as the Great Pacific Garbage Patch.

“Juvenile sea turtles generally have no specialised diet – they eat anything and 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.”

Researchers examined juvenile sea turtles – from hatchlings to a shell measurement of up to 50cm – that either washed up or were accidentally caught by fishers on the Australian coasts.

The study included a total of 121 sea turtles from five of the world’s seven species: green, loggerhead, hawksbill, olive ridley and flatback. According to the data, the proportion of turtles containing plastic was far higher on the Pacific coast with 86 per cent of loggerheads; 83 per cent of greens; 80 per cent of flatbacks, and 29 per cent of olive ridleys. On the Indian Ocean coast, 28 per cent of flatbacks; 21 per cent of loggerheads, and 9 per cent of green turtles contained plastic.

While no plastic was found in hawksbill turtles on either coast, only seven hawksbills were found so this sample size was considered too small to draw any firm conclusions.

The researchers found that plastic in the Pacific turtles was mostly hard fragments, which could come from a vast range of products used by humans, 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.

Dr Duncan said: “These polymers are so widely used in plastic products that it’s impossible to pin down the likely sources of the fragments we found. Hatchlings generally contained fragments up to about 5mm to 10mm in length and particle sizes went up along with the size of the turtles.

“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 with researchers and veterinarians around the world.”

The study was funded by the Sea Life Trust and the National Geographic Society and published in the journal Frontiers in Marine Science.

The problem of plastic pollution in the world's oceans continues to be a key area of focus for environmental scientists. According to a recent study by researchers from Sweden, Norway and Germany, the current rates of plastic emissions constitute a global threat and may trigger effects that we will not be able to reverse. Steps to drastically reduce plastic in the environment are “the rational policy response”, the study stated.

The widespread effects of plastic pollution is undeniable, further evidenced by the disturbing revelation that plastics have been found in seawater, on the beaches and inside marine animals around the ecologically pristine Galapagos Islands. Large quantities of plastic were found in all marine habitats at the island of San Cristobal, where Charles Darwin first landed in Galapagos, with up to 400 plastic particles collected per square metre of beach.

The build-up of microplastics in seafoods affects all living creatures - including humans. The threat may be underestimated, according to a separate study, and there is concern that microplastics could carry potentially harmful bacteria such as E. coli up the food chain.