A recent study reveals that whales hunting in the dark depths of the ocean may struggle to distinguish between plastic debris and their natural prey. Conducted by Greg Merrill, a graduate student at Duke University, the research was published in the Marine Pollution Bulletin.
The study found that 100% of the analyzed marine plastic debris emitted sound intensities similar to those of whale prey. Whales, such as sperm whales and pygmy sperm whales, rely on echolocation to find food in dark waters. They produce clicks and buzzes using a vocal structure filled with oil, which transmits sound through the surrounding water.
These sounds bounce off objects and are detected by sensory organs in the whales’ lower jaws, sending signals to their brains for interpretation. This echolocation system has been effective for over 25 million years, but the increasing presence of plastic in the oceans poses a significant threat. Plastic bags, ropes, and bottles are often found in the stomachs of stranded whales.
To assess whether whales are misled by plastic sounds, researchers tested acoustic signatures of typical beach debris collected from Beaufort and Atlantic Beach, North Carolina. The team utilized sonar on the Duke Marine Lab's R/V Shearwater to analyze the sounds emitted by plastic items like bags and balloons, commonly found in the stomachs of beached whales.
Acoustic tests were conducted at three sonar frequencies, covering the range used by deep-diving whale species. Comparisons were made with real squid samples to understand the differences in acoustic signatures.
The findings suggest that the various properties of plastics, such as chemical composition and size, likely influence how whales respond to these materials. While redesigning plastics to have less acoustic signature could be a solution, it may not be practical, as invisible fishing nets also pose a danger to whales.