Plastic Pollution: Looks Like Prey, Smells Like Prey to Turtles
Plastic pollution is an increasing threat to the world's oceans, and especially to a wide range of aquatic animals which become entangled in abandoned fishing gear, or accidentally ingest the plastic, mistaking it for food.
Turtles are particularly at risk; species such as leatherback, loggerhead and hawksbill turtles have been known to eat plastic bags, mistaking them for the jellyfish which form a staple part of their diets.
Research published in the online journal Current Biology, however, suggests that not only might turtles misinterpret the shape of the plastic bags as prey, but that scents acquired by the plastic during its time in the ocean may cause the turtle to think that it not only looks like a jellyfish, but that it also smells like a jellyfish.
The study involved presenting 15 captive loggerhead turtles (Caretta caretta) with odours released into the air above the tank in which the turtles were located, including scents derived from clean plastic, fish, shrimp, and plastic that had been removed from the ocean. The scientists found that when the turtles surfaced to breath, and sniff the air as if they were foraging for food, they responded to the ocean-soaked plastic in the same way they responded to the fish and shrimp.
'We found that loggerhead sea turtles respond to odours from biofouled plastics in the same way they respond to food odourants, suggesting that turtles may be attracted to plastic debris not only by the way it looks, but by the way it smells,' said the study's lead author, Joseph Pfaller of the University of Florida. 'This olfactory trap' might help to explain why sea turtles ingest and become entangled in plastic so frequently.'
The findings are based on previous research into the production of dimethyl sulfide, a gas generated by phytoplankton, which is consumed by other marine organisms such as shrimp and krill, which are in turn consumed by jellyfish. It produces a slightly unpleasant 'sea-smell' and is thought to be an indicator of the presence of prey for foraging seabirds.
Plastic that has been drifting in the ocean for some time accumulates a range of different organisms, including plankton and small fish and crustaceans, and generates the same odour that is naturally secreted by marine organisms.
'It’s common to find loggerhead turtles with their digestive systems fully or partially blocked because they’ve eaten plastic materials,' said Kenneth J Lohmann, a marine biologist from the University of North Carolina and one of the study's co-authors. 'This finding is important because it’s the first demonstration that the odour of ocean plastics causes animals to eat them.'
More research is required to better understand how plastic pollution is, perhaps, deliberately eaten by marine organisms, rather than a simple case of mistaken identity, but it clearly indicates that we are only just beginning to understand the scale of the problem that plastic pollution is causing in the world's oceans.
'The plastic problem in the ocean is more complex than plastic bags that look like jellyfish or the errant straw stuck in a turtle's nose,' said Pfaller. 'These are important and troubling pieces to the puzzle, and all plastics pose dangers to turtles.'