A growing awareness about the extent of plastic debris in the world’s oceans has prompted a number of studies into its impact on marine life. Graphic images of the stomach contents of dead turtles, fish, and seabirds have all suggested marine animals regularly ingest decaying bits of plastic, with lethal consequences.
A collaborative study led by former Institute of Marine and Antarctic Studies and CSIRO PhD student, Lauren Roman focused on the risk to seabirds from plastic debris. Published during March in the journal Scientific Reports the results showed soft plastics, and balloons in particular, pose the greatest mortality risk for the Procellariiformes bird group, that includes petrels, shearwaters and albatross. It is also the bird group recognised as being the most threatened due to its globally declining populations.
Using methodology developed from the approach taken for turtles, cause-of-death data was collected from 1733 seabirds from 51 species, and showed marine debris ranging from one to 40 items had been ingested by 557 seabirds. As all the study birds were from squid-feeding species, and they had all ingested balloons, scientists are concerned that the similarities between squid and balloon fragments may be causing birds to select for balloons when foraging.
Roman said the relationship between the type and amount of debris ingested by seabirds and their mortality remained poorly understood, and although soft plastics accounted for just five per cent of the items ingested, they were responsible for more than 40 per cent of the mortalities. She said all plastics posed a threat to seabirds but while hard plastics were less likely to kill than soft plastics, possibly due to them being the wrong shape and size to block a region in the birds’ gut, they were still responsible for more than half the seabird deaths identified in the study.
“Among the birds we studied the leading cause of death was blockage of the gastrointestinal tract, followed by infections or other complications caused by gastrointestinal obstructions. Balloons or balloon fragments were the marine debris most likely to cause mortality, perhaps because they can contort and squeeze into stomach cavities and get stuck, and they killed almost one in five of the seabirds that ingested them,” she said.
The study showed all plastics posed a mortal threat to seabirds and, ‘have substantial transboundary implications for estimating mortality due to marine debris ingestion and consequently managing wildlife population declines.’
“The evidence is clear. If we want to stop seabirds from dying from plastic ingestion, we need to reduce or remove marine debris from their environment, particularly balloons,” Roman said.
‘A quantitative analysis linking seabird mortality and marine debris ingestion’ is available at doi.org/10.1038/s41598-018-36585-9.