Plastic danger: Whales misled by ocean debris in echolocation

Scientists from Duke University conducted research suggesting that whales might mistake plastic debris for their natural food. Experts point out that plastic reflects sound in a way similar to some organisms on which whales feed.

"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," emphasized Greg Merrill, the lead author of the study, whose results were published in the journal "Marine Pollution Bulletin."

Whales, such as sperm whales, pygmy sperm whales, and beaked whales, use a highly developed sound reception system to locate food in the ocean's dark depths.

"One hundred percent of plastic marine debris tested have either similar or stronger acoustic target strengths compared with that of whale prey items," researchers noted.

Thanks to their specialized anatomical structure, whales generate sounds using formations resembling vocal cords near their nostrils. The "melon," an oil-filled structure above the head, transmits this acoustic wave into the water.

Receptors in the lower jaw capture the reflected sounds, and signals are sent to the inner ear and brain, allowing the whale to recognize objects in its environment. This system has been functioning for 25 million years, but plastic in the oceans disrupts its operation.

Every year, hundreds of thousands of tons of plastic waste enter the oceans, polluting the natural environment. While shopping, carrying plastic bags, using rubber balloons, or other consumer products, people often do not realize that these objects can be mistaken for food by marine mammals once they enter marine environments.

Scientists collected waste from a beach in North Carolina to determine how whales perceive plastic debris and tested its ultrasound reflections using sonar. "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," explained Merrill.

For comparison, researchers also tested real squids and fragments of this cephalopod's beak found in the remains of a sperm whale. The results indicated that plastic often exhibited similar acoustic properties to the whales' food.

Although one potential solution to the problem could be redesigning plastics to eliminate their distinct acoustic signatures, the authors are unsure if this is feasible.

"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," added Greg Merrill.