Scientists claim sea turtles find discarded pieces of plastic appetising because it can look and smell like food to them.
Previous research had suggested that sea turtles 'visually mistake plastic debris such as plastic bags for jellyfish prey'. But researchers have now cast doubt on that suggesting: "Sea turtles also ingest other plastics that bear no clear resemblance to jellyfish and occasionally become entangled in large mats of plastic debris that presumably are not being confused with food.
"The ‘plastic-jellyfish’ hypothesis therefore fails to capture the true scope of interactions between turtles and plastic debris or the sensory mechanisms involved. Instead, our findings provide a possible unifying explanation for why such incidents frequently occur."
The paper published in Current Biology says despite the dangers of plastic debris for sea animals 'little is known about the sensory mechanisms that drive wildlife to interact with plastic debris'.
It suggests: "Marine animals may be attracted to plastic debris not only by the way it looks, but also by the way it smells."
Experiments were conducted on 15 captive-reared loggerhead turtles collected from Bald Head Island, North Carolina, each approximately five months of age.
The study, funded by the National Science Foundation, involved the University of North Carolina and University of Georgia Marine Extension on Skidaway Island, Georgia.
A spokesperson for the study explained: "Previous studies have shown that sea turtles can
detect airborne odourants - including odours from food and dimethyl sulfide, a volatile organic compound found in productive oceanic foraging areas.
"In response to these sensory cues, turtles become more active and spend more time with their nares protruding out of the water - behaviour that presumably reflects increased sampling of the air and represents the start of foraging behaviour.
"We used the time that each turtle spent with its nares out of the water and the number of breaths taken as objective behavioural responses to different experimental treatments.
"Our results indicate that odours from food and biofouled plastic elicited indistinguishable behavioural responses, which were significantly stronger than responses to other treatments.
"Specifically, we found that turtles kept their nares out of the water more than three times longer in response to odours from their food and biofouled plastic relative to control odours.
"We found the same qualitative pattern for the number of breaths taken by turtles.
"These results indicate that sea turtles can detect airborne odourants emanating from biofouled plastic and respond to them in the same way that they respond to food odours.
"Moreover, these findings are consistent with the hypothesis that odours emanating from biofouled plastic stimulate foraging behaviour in sea turtles and contribute to turtles’ attraction to marine plastic debris."
How was the research conducted?
Following a 20-minute air-out period to remove all residual odours, each turtle was placed gently in an experimental arena and allowed to acclimate for approximately one minute prior to adding a stimulus .
Airborne odourants were delivered through a pipe into the experimental arena where the behaviour of the turtle was video recorded .
Odours were allowed to accumulate for two minutes in the arena; then, after the turtle surfaced to breathe and could thus sample airborne odourants, we collected behavioral data for four minutes.
Each turtle was exposed to four different treatments in random order: deionised water (100 ml); turtle food (a minced 20 g pellet containing fish and shrimp meal); clean plastic (one empty 500 ml water bottle cut into 10 equal pieces); and biofouled plastic (one empty 500 ml water bottle exposed to biofouling by micro- and macro-biota for five weeks in the marine environment and cut into 10 equal pieces).
For biofouled plastic, we took care not to remove biofilms or dislodge fouling organisms following the biofouling period, and we used a different biofouled plastic bottle for each trial.
For more about the study click here