How Boats Are a Buzzkill for Porpoises

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P.orpoises are fish-eating machines. A study on harbor porpoises (Phocoena phocoena) in Denmark, they consumed up to 200 fish per day, then fed in the evening in deep waters. Since they rely on echolocation to find and capture prey, you can count on a porpoise making clicks almost continuously during waking hours. The high-frequency clicks of around 135 kilohertz produce a rat-a-tat-tat that is inaudible to us but essential to a porpoise.

To understand whether ship noise interferes with porpoise echolocation, biologists from universities in the United Kingdom and Denmark deployed underwater microphones in a narrow strait. The “Little Belt” between the island of Funen in Denmark and the Jutland peninsula, near the port of Fredericia which welcomes more than 2,500 ships per year, brings large ships and porpoises into close contact. Additionally, an endangered population of harbor porpoise depends on the strait for its concentrations of eelgrass and associated fish species.

“This study contributes to a growing understanding of how underwater noise and increasing maritime traffic affect our environment, and in particular a noise-sensitive species like the harbor porpoise,” Jonas Teilmann, study author and marine mammal researcher at Aarhus University, said in a statement.

Read more: “Swimming in the Noise”

The results of three years and two months of hydrophone monitoring, published in Marine Mammal Science yesterday, showed that harbor porpoises “buzz” less when ships pass below about 3,000 meters. Their buzz rates were reduced by up to 40 percent during the busiest maritime traffic periods, concentrated on summer days. This occurred immediately in response to the arrival of nearby ships, suggesting that even brief encounters with boat noise can disrupt the porpoises’ foraging.

Although harbor porpoises are often solitary or in small groups, they rely on echolocation clicks to communicate with their babies and each other. Thus, their social behavior may also be stifled by maritime traffic.

“Although we did not directly assess the impact of shipping traffic on porpoise populations, the disruptions we saw will likely affect their ability to cope with other environmental stressors,” explained co-lead author Shannon Merkle, now with NOAA Fisheries.

Because they rely on prey concentrated in the Little Belt, this porpoise population would have difficulty moving elsewhere.

Whether from shipping traffic, fishing activities, construction, offshore energy exploration or other activities, human-caused noise will likely continue to increase around Denmark and other coastal regions around the world. This is why the study results call for more attention to be paid to the effects of anthropogenic noise on porpoises and other coastal species.

Basically, we need to soothe our ribs.

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Main image: Ecomare/Salko de Wolf/Wikimedia Commons

• Devin Reese

  Published on February 10, 2026

  Devin Reese is the editor-in-chief of Natural history and a science writer based in Alexandria, Virginia.