Even When It Doesn't Kill Them, Plastic Hurts Seabirds

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©. Flesh-footed shearwater with plastic ingested and recovered from the bird's stomach. (Photo: Cameron Muir)

A new study looks at the non-lethal effects of seabirds' plastic ingestion.

Friedrich Nietzsche famously wrote, more or less, "what does not kill me makes me stronger."

Unfortunately, no matter how many coffee mugs the aphorism may adorn, it doesn't seem to be working for seabirds when it comes to plastic debris.

We know that plastic pollution and wildlife make for a tragic combination, but our current knowledge of the impact is generally limited to what we can see; nightmarish images of entanglement and stomachs emptied of plastic bits. But as researchers from the Institute for Marine and Antarctic Studies (IMAS) explain, interactions with debris result in less visible and poorly documented sublethal effects, and as a consequence, the true impact of plastic is underestimated.

With that in mind, IMAS decided to investigate how plastic ingestion was hurting the birds that were managing to survive.

The study led by Dr Jennifer Lavers, from IMAS, and published in the journal Environmental Science & Technology found that plastic ingestion can have a significant negative impact.

The IMAS researchers teamed up with scientists from the Lord Howe Island Museum and the UK's Natural History Museum, to analyze blood and plastic samples collected from flesh-footed shearwaters on Lord Howe Island.

"Flesh-footed Shearwaters populations are declining across the south west Pacific Ocean and Western Australia's south coast,"Lavers said. "Plastic ingestion has been implicated in this decline but the mechanisms by which it affects shearwaters are poorly understood.

"Our study found that birds which ingested plastic had reduced blood calcium levels, body mass, wing length, and head and bill length," she said. "The presence of plastic also had a negative impact on the birds' kidney function, causing a higher concentration of uric acid, as well as on their cholesterol and enzymes."

Surprisingly, they found that the amount of plastic ingested didn't necessarily correlate with the damage done; just the presence of it was enough to cause harm, regardless of the amount.

"Our data did not show a significant relationship between the volume of plastic ingested and the health of individuals, suggesting that any plastic ingestion is sufficient to have an impact. Until now there has been scant information on the blood composition of seabirds in the wild, many of which have been identified as threatened species."

"Understanding how individual seabirds are affected is also further complicated by the fact they spend little time on land or at breeding colonies, and most mortalities occur at sea where the causes of death are often unknown. The complex range of issues that face seabirds – from habitat loss and climate change to fishing and marine pollution – make it vital that we better understand the impact of particular challenges such as plastic debris," Dr Lavers said.