To whales that rely on sound to hunt in the dark depths of the ocean, a deflated plastic balloon can seem strikingly similar to a tasty squid, as revealed by a recent study. Research involving underwater sound testing on beach plastic showed that these items often produce sounds mimicking food, particularly with plastic films and small plastic pieces—two types that frequently end up inside deceased whales.
In the pitch-black depths of the ocean, whales that hunt using soundwaves find it hard to distinguish between a torn party balloon and a scrumptious squid, according to research that subjected various pieces of plastic trash to underwater sound tests.
“These sound signatures are quite alike, which may explain why these creatures sometimes consume plastic in place of or alongside their actual prey,” explained Greg Merrill, a graduate student from Duke University who led the study.
“All tested marine debris made from plastic displayed either similar or even more pronounced sound reflection strengths compared to whale prey,” the researchers noted in their publication in Marine Pollution Bulletin.
To locate food in the dark, deep-diving whales like sperm whales, pygmy sperm whales, and goose-beaked whales generate clicks and buzzes from a structure near their blowholes that acts like a vocal cord. These sounds travel through the water via a rounded, oil-filled structure called a ‘melon’ located above their mouths. The echoes bouncing back from surrounding objects are detected by fat-filled sensory organs in their lower jaws, which then transmit the signals to their inner ears and brains for processing. This method has been effective for them for over 25 million years.
Nevertheless, the presence of ocean plastics—like shopping bags, ropes, and bottles—has become an increasing concern, often discovered in the digestive tracts of stranded whales and other sea creatures. To determine if whales might mistake plastics for food due to sound confusion, Merrill conducted this study.
The researchers gathered common beach plastic debris—some even covered in barnacles—from the beaches in Beaufort and nearby Atlantic Beach, North Carolina. They then subjected these items to testing using the sonar transponder aboard the Duke Marine Lab’s ship R/V Shearwater. “We were working with plastic bags, balloons, and other items that are frequently found in the stomachs of stranded whales,” said Merrill.
An H-shaped rig was constructed using fishing line to suspend the samples four to five meters beneath the transponder, located at the bottom of one of the catamaran’s keels. Acoustic testing was carried out using three sonar frequencies: 38, 70, and 120 kilohertz, which correspond to the sound clicks made by various deep-diving whale species.
As a benchmark, they also examined actual squid and squid beak pieces obtained from the stomach of a deceased sperm whale.
The testing revealed that plastic materials almost always produced sounds resembling food, particularly plastic films and fragments, which are notably prevalent in deceased whales.
“With hundreds of different types of plastic, various factors such as chemical makeup, additives, shape, size, age, exposure to the elements, and level of fouling all likely influence the distinct sound responses observed,” the authors wrote.
It may be possible to modify certain plastics to eliminate their acoustic signatures, suggested Merrill. “However, that might not be practical, since making fishing nets and lines ‘invisible’ would only lead to more whale entanglement issues. We need to ensure whales can still recognize those dangers.”
Merrill collaborated with scientists from nearby marine facilities run by NOAA, NC State University, and UNC – Chapel Hill for this project.
