(CN) – Male humpback whales react to human-generated shipping noise by reducing or ceasing their songs, according to a study published Wednesday in the journal PLOS ONE.
Increasing human shipping activity creates a rise in low-frequency ocean noise. Whales use low-frequency sound to communicate, so man-made noise could affect their singing behavior, according to lead author Koki Tsujii and colleagues from Ogasawara Whale Watching Association and Hokkaido University, Japan.
"Humpback whales seemed to stop singing temporarily rather than modifying sound characteristics of their song under the noise, generated by a passenger-cargo liner. Ceasing vocalization and moving away could be cost-effective adaptations to the fast-moving noise source," Tsujii said.
Only male humpback whales sing, so recordings cannot indicate if or how females and calves are reacting to ship noise. The study captured one to three singing whales per day out of a total of 26 singers. Even with the small sample size, the findings suggest ship noise can temporarily affect singing behavior of humpbacks, and future research could investigate the effects of more continuous noise exposure as a possible stressor for the whales.
Researchers studied the effects of a passenger-cargo ship's noise on the songs of male humpback whales living around the Ogasawara Islands in Japan. They used two underwater recorders to capture the singing and locations of animals between February and May 2017, and examined the effect on humpback singing of the noise of the passing ship, the only large boat travelling in this remote area.
Ocean noise caused by human activities has increased by 10 decibels between the 1960s and the 1990s. Noise sources include seismic explosions, transportation, harvesting renewable energy and military sonar, with the main noise source presumed to be from commercial ships.
Fewer male humpbacks sang within 500 meters of the shipping lane than elsewhere, the authors discovered. After the ship passed by, whales within around 1,200 meters tended to temporarily reduce singing or stop singing altogether.
Although they did not show other adaptations such as changing the frequency of their songs, most waited at least 30 minutes to resume singing until after the ship had passed by.
The Japan Ship Technology Research Association and Nippon Foundation provided funding for the underwater noise project.