Hungry seals provide direct evidence that plastic travels up the ocean food chain from prey to predator.

Researchers have long assumed that marine predators ingest microscopic fragments of plastic by eating prey filled with it. To test this idea, Penelope Lindeque at the Plymouth Marine Laboratory, UK, and her team analysed faeces from captive male grey seals (Halichoerus grypus) at a seal sanctuary. The team also dissected the digestive tracts of wild-caught Atlantic mackerel (Scomber scombrus), which are fed intact to the predators.

Almost one-third of the fish and nearly half of the seal-faeces samples contained one to four plastic fibres and fragments. Among the most common was polyethylene, which is found in plastic bags and bottles.

The results confirm that microplastics can be transferred from prey to predators at the top of the food chain. Such transmission could magnify the effects of toxic pollutants stuck to the plastic, the authors say.