Acoustic study documents humpback whales move daytime singing offshore
The study is the first of its kind using specialized acoustic sensors to localize individual singers relatively close to shore to understand daily variations in the whale’s spacing and movement behavior.
By Susan Enright.
Marine mammal scientist Adam Pack, a professor with joint appointments in the psychology and biology departments at the University of Hawaiʻi at Hilo, is a co-author of a study documenting a daily pattern as humpback whales, near Maui during the winter months, move their singing away from shore throughout the day and return to the nearshore in the evening.
The findings were led by UH, in partnership with the National Oceanic and Atmospheric Administration’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,” says 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.”
Kügler was Pack’s student at UH Mānoa, where he is a cooperating faculty member of the marine biology graduate program. He served as Kügler’s co-advisor with Marc Lammers, a research ecologist with NOAA’s Hawaiian Islands Humpback Whale National Marine Sanctuary who also is a co-author of the newly published study.
“As her mentor,” explains Pack, “I helped Anke design the shore-based humpback whale portion of the study in which she conducted systematic scan samples from a hill near Olowalu on West Maui for the presence and pod composition of humpback whales in waters stretching across the Auʻau channel between Maui, Molokai, Lānaʻi and Kahoʻolawe.”
Scans occurred for 30 minutes every hour over the course of the day starting at 8:00 or 8:30 a.m. one to three times each week throughout the whale breeding season. A surveyor’s theodolite was used to pinpoint the precise coordinates of sighted pods, which could then be converted by a computer to longitude and latitude.
“Compiled data allowed us to track the offshore and in-shore diurnal movements of whale pods including those likely to contain singers,” says Pack.
Kügler says, to the research team’s knowledge, the study is the first of its kind “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.”
As her mentor and a co-author on the study, Pack also assisted Kügler in determining how best to analyze the acoustic data as well as how to organize and write various sections of the manuscript.
A major focus of Pack’s Marine Mammal Laboratory at UH Hilo is making discoveries to best characterize the humpback whale mating system. Each winter and spring season, male humpback whales congregate in Hawaiʻi waters where they not only physically compete for access to single females in competitive groups, but where they also “sing.”
“Humpback whale song is one of the most complex vocal displays in the animal kingdom,” says Pack, who is a co-founder of UH Hilo’s Listening Observatory for Hawaiian Ecosystems bioacoustics lab, commonly called the LOHE Lab. “Song is an integral part of the humpback whale mating system. The current paper provides new and exciting information on how singing males move throughout the day to maximize transmission of song advertising their locations not only to females but to other males with whom they may eventually be competing with.”
Listen to recording of a humpback whale chorus off Maui with numerous males singing (Oceanwide Science Institute):
Pack further explains that during the day while offshore, singing males may be more likely to encounter females without a calf which have a higher reproductive potential than mothers. At night, singers move inshore possibly to reduce acoustic interference from other naturally occurring marine organisms located in deeper water.
Lammers says 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.”
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,” says 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,” says 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.”
Aaron Thode and Ludovic Tenorio-Hallé at Scripps Institute of Oceanography, University of California, are also co-authors of the study.
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.
Learn more about Adam Pack’s acoustic research with whales:
Story by Susan Enright, a public information specialist for the Office of the Chancellor and editor of UH Hilo Stories. She received her bachelor of arts in English and certificate in women’s studies from UH Hilo.