When searching for food in the dark, deep-diving whales rely on their built-in sonar to bounce sound waves off potential prey and reveal its location. But this amazing ability can also have its drawbacks.

Researchers at Duke University's Marine Laboratory in Beaufort, New York, have found that the strength of the echoes returned by plastic debris is similar to that of common whale prey. Plastic debris, such as shopping bags, has a remarkably similar "echo" to squid. This is likely due to a combination of their shape, size, degree of weathering, and chemical composition.

This can fool sperm whales, sperm whales and other deep-diving whales. The whales, some of which dive to depths of nearly 3,000 meters, mistake plastic objects for prey. Such mistakes can be fatal, as the plastic fills their stomachs and intestines and can prevent food from passing through.

Plastic ends up in the intestines of marine mammals, damaging their stomach tissues and causing infections, choking, and malnutrition, even starvation. Whales washed up around the world have tens of kilograms of plastic waste in their stomachs.

Sharks and fish can also mistake plastic for prey thanks to visual cues.

Acoustic plastic replacement

When searching for food in the dark, deep-diving whales rely on their built-in sonar to bounce sound waves off potential prey and reveal its location. But this amazing ability can also have its drawbacks.

Researchers at Duke University's Marine Laboratory in Beaufort, New York, have found that the strength of the echoes returned by plastic debris is similar to that of common whale prey. Plastic debris, such as shopping bags, has a remarkably similar "echo" to squid. This is likely due to a combination of their shape, size, degree of weathering, and chemical composition.

This can fool sperm whales, sperm whales and other deep-diving whales. The whales, some of which dive to depths of nearly 3,000 meters, mistake plastic objects for prey. Such mistakes can be fatal, as the plastic fills their stomachs and intestines and can prevent food from passing through.

Plastic ends up in the intestines of marine mammals, damaging their stomach tissues and causing infections, choking, and malnutrition, even starvation. Whales washed up around the world have tens of kilograms of plastic waste in their stomachs.

Sharks and fish can also mistake plastic for prey thanks to visual cues.

Millions of tons of plastic enter the world's oceans every year, totaling tens of trillions of plastic debris.

Biologist Greg Merrill and his colleagues tested the echogenicity of nine pieces of plastic debris collected directly from the sea—ropes, bags, bottles, and other objects commonly found in whale stomachs. The team also tested octopuses, which resemble their prey. They placed the plastic objects and the prey on an underwater device and blasted them with sounds at frequencies of 38, 70, and 120 kHz, which cover the range used by whales for echolocation.

All of the plastic objects returned echoes that were similarly strong, or sometimes even stronger, than those from prey. The findings, the researchers say, provide a case for modifying the composition of plastics to prevent them from being acoustically mistaken for natural prey.

Before plastics were invented, anything whales encountered in the deep ocean that echoed loudly enough was likely biological and edible. They don't expect to see anything other than food in the water.

Possible solutions

Plastic manufacturers could try to make plastics that sound less like prey, or replace existing plastics with biodegradable materials that break down quickly in the ocean or in the stomachs of whales.