It’s no secret noise pollution can have some serious ramifications for terrestrial wildlife, and it's no different under the ocean's surface. From deafness to death, detrimental effects have been recorded in animals as small as the pistol “snapping” shrimp and as big as the mighty blue whale.

Dutch researchers now say harbor porpoises lose their appetite and flee after hearing noise from ships. It’s the first time scientists have recorded how Denmark’s porpoises respond to heavy ship noise in one of the world's most trafficked waterways. 

Researchers collaborated with Danish fishermen, who often accidentally catch porpoises in their nets, to tag the marine mammals. After a quick phone call, the scientists were on the ship within a matter of hours to take stock of the sex, size, and health of the creatures before fitting them with electronic tagging devices (ETD) stuck to their backs with suction cups.

The electronic tags recorded sounds from seven porpoises as well as the noise from ships to see when the animals feed and at what depth they stay. 

"When the ship noise exceeds a certain level, the porpoises stop feeding," says senior researcher Jonas Teilmann in a statement. "At very high sound levels the animals dive to the bottom and move fastly along this, and they cease emitting the biosonar clicking sounds that they use when searching for food."

Harbor porpoises are found in temperate waters around the world and tend to stay near the surface to feed. While they resurface around every 25 minutes, they can dive to depths of more than 200 meters (655 feet).

Getting caught in fishing nets may prove detrimental to populations despite its usefulness in this study. Between 2006 and 2008, it’s estimated nearly 21,000 porpoises were caught by mistake off the coast of Norway in boats fishing for cod and monkfish.

Sounds caused by humans from shipping, oil and gas development, naval sonar training, tourism, fishing, and construction can negatively impact marine life that are sensitive to the noise. Extreme noise pollution created by offshore activities have reportedly killed hundreds of dolphins and whales at a time. For vulnerable populations like the Pacific Bryde’s whale, this could mean extinction before our eyes.

But the researchers of this latest study, published in the journal Proceedings of the Royal Society B, aren’t sure how far this damage goes.

"Our measurements show that the porpoises do respond to heavy ship noise," said co-author Peter Teglberg Madsen ofAarhus University. "It is still too early to say, though, what this means to the well-being of the porpoises, their production of offspring and, in the long term, their survival."