VNR: Humpback whale singers move depending on time of day

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Humpback whale singing dominates the marine soundscape during winter months off Maui. New research revealed a daily pattern wherein whales move their singing away from shore throughout the day and return to the nearshore in the evening. The findings were led by the University of Hawaiʻi, in partnership with NOAA's Hawaiian Islands Humpback Whale National Marine Sanctuary, and published in Royal Society Open Science.

"Singers may be attempting to reduce the chances of their song being drowned out among the cacophony nearshore when whale numbers are high," said Anke Kügler, lead author of the study who was a UH Mānoa doctoral student in the Marine Biology Graduate Program at the time of the research. "Further, we documented humpback whales moving closer to shore around sunset, possibly to avoid the offshore evening chorus of other animals."

By using a combination of underwater listening devices and visual surveys, the research team was able to track both the physical movements and the acoustic patterns of whales in the high-density breeding grounds found in Hawaiʻi.

"This dynamic onshore-offshore movement of singers may be aimed at increasing the efficiency of the whales' acoustic display, ensuring that other whales hear their songs," said Marc Lammers, study co-author and research ecologist with NOAA's Hawaiian Islands Humpback Whale National Marine Sanctuary.

"This is the first effort of its kind, to our knowledge, in which we used specialized acoustic sensors to localize individual singers relatively close to shore to understand daily variations in the distance to shore of these nearshore singers, their spacing, and their movement behavior," said Kügler.

Important role for breeding

Humpback whale song is presumed to play an important role for breeding. The findings highlight the significance for male singers in an environment that is teeming with acoustic commotion. Through their approach, the team identified potential drivers for the daily onshore-offshore migrations-nearshore environments that are too crowded with whales during the day and offshore areas that are too noisy with the chorus of other animals in the evening.

"Discussions of noise pollution related to marine mammals have been dominated by concerns over anthropogenic noise," said Kügler. "How natural sounds, including from other humpback whales, may interfere with their singing has been mostly overlooked. Humpback whales rely on acoustic signals. We explored possible causes of the observed patterns, which helps us understand how these whales adopt behavioral strategies that reduce interference from loud environments."

Humpback whales are ecologically, economically and culturally significant in Hawaiʻi, and their singing is iconic around the world.

"It is our collective kuleana (responsibility) to be the koholā's (humpback whales) stewards," said Lammers. "This and future work contributes to fulfilling the sanctuary's management plan by developing and implementing crucial research on humpback whales and their habitats to help maintain a healthy, sustainable population."

Co-authors on the study include Adam Pack, professor of psychology and biology at UH Hilo, founder and director of the UH Hilo Marine Mammal Lab and co-founder of the LOHE bioacoustics lab; and Aaron Thode and Ludovic Tenorio-Hallé at Scripps Institute of Oceanography, University of California.

The work was supported by funding or in-kind donations provided by Oceanwide Science Institute, Greeneridge Science Inc., Whale Tales/Whale Trust Maui, the Linda and Jim Collister Fellowship, Pride of Maui, Trilogy Maui and Ultimate Whale Watch.