Fish eat bits of plastic because they think they smell good

by Josh Gabbatiss on 17 Aug 2017 Editor's Note: The New Scientist reports on how it has been proven that it is the smell of the plastics in the ocean that is attracting marine life to eat them, and not necessarily the weed and algae that grows on them. This is quite revelatory, and of course, the impacts to all who eat seafood, which includes us humans is yet to be fully understood. In this excellent article, some of the issues are uncovered...

Hundreds of marine species are known to eat plastic – including those that regularly end up on our dinner plates. But why? It now seems that ocean-borne plastic has a smell that marine animals find appealing.

Matthew Savoca at the NOAA Southwest Fisheries Science Center in Monterey, California, explored the dietary preferences of marine life while he was a researcher at the University of California, Davis. He and his colleagues exposed schools of anchovies to seawater that contained odours from plastic. To make this, they left plastic beads in the ocean for three weeks, then stirred the beads into seawater samples before filtering them out – leaving just the associated odour chemicals.

In the ocean, plastic quickly becomes covered with a layer of algae that releases smelly sulphur compounds. Foraging fish such as anchovies, which feed on algae-munching marine crustaceans called krill, are thought to use these compounds to help them locate their prey.

When analysing videos of the anchovies, the researchers noticed that the fish reacted to the fouled plastic solutions as if they were their crustacean prey. The decision to use solutions that smelled of plastic rather than actual pieces of plastic meant the fish weren’t responding to visual cues; the fish must have smelled the odours. They did not respond to clean plastic.

The work builds on Savoca’s earlier research, which suggested that similar sulphurous odours lure tube-nosed seabirds – which are also krill-feeders – into eating plastic.

Fish aren’t stupid

“This problem of animals eating plastic has not been investigated as completely as it should have been,” says Savoca. Seabirds and fish aren’t stupid, he says, and generally they are good at locating the correct prey. Savoca thinks we might have overlooked the role of odour because we are such visual animals. “That’s how we perceive the world most readily.”

To find out more visit www.newscientist.com/article/2143869-fish-eat-bits-of-plastic-because-they-think-they-smell-good