Predicted probability of debris ingestion risk for each sea turtle species (from 0-1). Red indicates a high probability of debris ingestion while lighter colours indicate lower probability of debris ingestion. Blue dots indicate the location of studies used to parameterize the risk model. Graphic: Schuyler, et al., 2015 / Global Change Biology

16 September 2015 (Plastic Pollution Coalition) – A new international study published on 14 September 2015, led by a University of Queensland researcher, has suggested that more than half the world’s sea turtles have ingested plastic or other human rubbish.

The study, led by Dr. Qamar Schuyler from UQ’s School of Biological Sciences, found the east coasts of Australia and North America, Southeast Asia, southern Africa, and Hawaii were particularly dangerous for turtles due to a combination of debris loads and high species diversity.

The study examined threats to six marine turtle species from an estimated 4 to 12 million tons of plastic that enter the oceans annually. Approximately 52 percent of turtles worldwide have eaten debris, according to Schuyler.

Plastic ingestion can kill turtles by blocking the gut or piercing the gut wall, and can cause other problems through the release of toxic chemicals into the animals’ tissues.

“Australia and North America are lucky to host a number of turtle species, but we also therefore have a responsibility to look after our endangered wildlife,” Schuyler said. “One way to do that is to reduce the amount of debris entering the oceans via our rivers and coastlines.”

A previous study by Schuyler and colleagues showed that plastics and other litter that entered the marine environment were mistaken for food or eaten accidentally by turtles and other wildlife.

The risk analysis found that Olive Ridley turtles (Lepidochelys olivacea) were at the highest risk, due to their feeding behavior and distribution. Olive Ridley turtles commonly eat jellyfish and other floating animals, and often feed in the open ocean, where debris accumulates.

This research echoes the results of a similar study on seabirds published two weeks ago by CSIRO collaborator Dr. Chris Wilcox and colleagues, which found that more than 60 percent of seabird species had ingested debris, and that number was expected to reach 99 per cent by 2050.

“We now know that both sea turtles and seabirds are experiencing very high levels of debris ingestion, and that the issue is growing,” Wilcox said. “It is only a matter of time before we see the same problems in other species, and even in the fish we eat.”

Over Half the World's Sea Turtles Have Eaten Plastic

ABSTRACT: Plastic marine debris pollution is rapidly becoming one of the critical environmental concerns facing wildlife in the 21st century. Here we present a risk analysis for plastic ingestion by sea turtles on a global scale. We combined global marine plastic distributions based on ocean drifter data with sea turtle habitat maps to predict exposure levels to plastic pollution. Empirical data from necropsies of deceased animals were then utilised to assess the consequence of exposure to plastics. We modelled the risk (probability of debris ingestion) by incorporating exposure to debris and consequence of exposure, and included life history stage, species of sea turtle and date of stranding observation as possible additional explanatory factors. Life history stage is the best predictor of debris ingestion, but the best-fit model also incorporates encounter rates within a limited distance from stranding location, marine debris predictions specific to the date of the stranding study and turtle species. There is no difference in ingestion rates between stranded turtles vs. those caught as bycatch from fishing activity, suggesting that stranded animals are not a biased representation of debris ingestion rates in the background population. Oceanic life-stage sea turtles are at the highest risk of debris ingestion, and olive ridley turtles are the most at-risk species. The regions of highest risk to global sea turtle populations are off of the east coasts of the USA, Australia and South Africa; the east Indian Ocean, and Southeast Asia. Model results can be used to predict the number of sea turtles globally at risk of debris ingestion. Based on currently available data, initial calculations indicate that up to 52% of sea turtles may have ingested debris.

Risk analysis reveals global hotspots for marine debris ingestion by sea turtles



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