A groundbreaking study reveals deep-diving whales often mistake plastic debris for food due to similar acoustic signatures. This finding underscores the pressing need to tackle marine plastic pollution.
To whales hunting with soundwaves in the depths of the ocean, a torn plastic party balloon can sound alarmingly similar to a delicious squid. According to new research led by Duke University, echo-locating whales are potentially driven to consume plastic debris instead of — or in addition to — their natural prey.
“These acoustic signatures are similar, and this might be a reason that these animals are driven to consume plastic instead of, or in addition to, their prey,” lead author Greg Merrill, a Duke University graduate student, said in a news release.
The study, published in Marine Pollution Bulletin, highlighted that 100% of the plastic marine debris tested had acoustic target strengths either similar or stronger compared to those of whale prey items.
To uncover these findings, Merrill and his team collected various plastic items from beaches in Beaufort and Atlantic Beach, N.C. They then subjected these plastics to underwater acoustic testing using the sonar transponder on the Duke Marine Lab’s ship, R/V Shearwater. The trash items tested included plastic bags and balloons, which are frequently found in the stomachs of stranded whales.
“It was plastic bags, balloons, things that are commonly observed in the stomachs of stranded whales,” Merrill added.
The team devised an H-shaped rig of fishing line to suspend these samples below the ship’s transponder. They tested the acoustic signatures at three different sonar frequencies — 38, 70 and 120 kilohertz — covering the range of ‘clicks’ utilized by different species of deep-diving whales.
The researchers found that these plastics, especially plastic films and fragmented plastic pieces, emitted acoustic signatures that closely mimicked those of real squid and squid beaks, often found in the digestive tracts of deceased whales.
“There are hundreds of types of plastic, and the various material properties including polymer (chemical) composition, additives, shape, size, age/weathering and degree of fouling likely play a role in the frequency-specific responses observed,” reported the research team.
While Merrill mused that re-engineering plastics to lack acoustic signatures might theoretically prevent whales from mistaking them for food, he acknowledged the practical dangers this posed.
“But I don’t think that’s really a viable option, because then, if fishing net and fishing line are invisible, those are things that whales get entangled with, too. So we don’t want them to not be able to identify those things,” he added.
Merrill collaborated with scientists from NOAA, NC State University and UNC-Chapel Hill for this study, further underscoring the collaborative effort required to address this critical environmental issue.
As millions of metric tons of plastic enter the oceans each year, the findings of this study highlight an urgent need to find solutions to marine plastic pollution. Deep-diving whales, essential to marine ecosystems, are at significant risk, emphasizing the broader environmental and ecological implications.