The majestic humpback whale (Megaptera novaeangliae) is one of the best-known vocalists in the ocean and possesses the ability to communicate to other whales with a series of repetitious sounds at different frequencies. All whales living in the same area sing the same song and the song itself is slowly evolving over time. Although research is ongoing, it is thought that the main purpose of the ‘whale song’ is to help attract a mate during breeding season or to help mark out territory.
However, there has been growing concern surrounding the effects of noise pollution on marine creatures, especially cetaceans (whales, dolphins, and porpoises). Studies have already begun to show that noise pollution from human shipping activities can affect feeding behaviour in cetaceans as well as produce an increase in stress and decrease the number of singing individuals in a population. Baleen whales such as the humpback whale are thought to be very sensitive to low frequency sounds like those produced by boats, this means that evaluating their response is critical if we are to see how their populations might be affected in the future.
Koki Tsujii and colleagues 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 traveling in this remote area.
“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.
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. In terms of cost to the individual, the team believes that whales might choose to cease vocalization and move away from noise source rather than adjusting their calls under a high noise level condition.
By Ellis Moloney
Tsujii, K., Akamatsu, T., Okamoto, R., Mori, K., Mitani, Y. and Umeda, N. (2018). Change in singing behavior of humpback whales caused by shipping noise. PLOS ONE, 13(10), p.e0204112.
The Japan Ship Technology Research Association and Nippon Foundation provided funding for the underwater noise project.
