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Shared songs indicate ongoing mixing of humpback whale populations across the North Pacific

By Staff | Jun 20, 2019

Current National Marine Fisheries Service humpback whale management policies assume four distinct populations in the North Pacific. Song studies suggest an alternate population model is warranted. A singer from the 2019 season is pictured. PHOTO BY RALPH PACE, MINDEN PICTURES, NMFS PERMIT 19225.

MAUI – Whale Trust researchers and international colleagues last week announced the publication of a multi-year study involving song comparison between four locations spanning the North Pacific in Scientific Reports.

Shared song composition between humpback whales found in the Philippines, Japan, Hawaii and Mexico in winter indicates ongoing mixing of “populations” at some point during their annual cycles.

Convergence of song over this three-year period recalls similar song transmission when humpback whales off the east coast of Australia adopted a song from a western Australia population during a study in the late 1990s.

“Mixing may be the rule, not the exception, and part of the biology of North Pacific humpback whales,” said project leader Dr. Jim Darling, who has spent his career studying humpback whale singers and their song.

Studies over at least 35 years (1977-2013) have shown humpback whales in these different winter assemblies have shared all, or portions, of these ever-changing complex songs, as cited in a comparison included in this study.

The common song across the North Pacific over the long term indicates ocean-wide interaction and the composition’s fluid nature, annual variable mixing. While acoustic contact is necessary to song transmission, Darling cautions its mechanics, and the purpose of the song for the whales, are not fully understood.

For scientists, the song provides an acoustic identity, since each singer in a “population” sings the same version of the ever-changing song. Singers, exclusively male, broadcast the song starting in fall, continuing through the winter migrations and tapering off in spring before summer feeding.

Recorded by hydrophone by teams of scientists across these four locations, the song’s composition was compared and analyzed by Darling.

“Song composition appears to reflect the recent interactions of populations of whales,” said Darling.

Shared song suggests these populations may not be as independent of one another as outlined by management policies in effect. While Hawaiian humpbacks were delisted from endangered status in 2016, a reevaluation of their relationship with populations in Asia and Mexico may be warranted.

“Song should be considered when defining humpback whale populations across the North Pacific,” said Darling.

Currently, NOAA/NMFS (National Marine Fisheries Service) does not include song amongst the data determining populations.

“We may be making decisions around population management based on a model which doesn’t reflect humpback whale behavior in the North Pacific,” Darling noted.

According to Whale Trust, this question must be posed: how can Mexico whales be “threatened” and Asian whales “endangered,” but Hawaii whales “warrant no protection” when it’s clear all three groups are integrated?

“We have been delighted to collaborate with Dr. Jo Marie Acebes in the Philippines; Manami Yamaguchi in Ogasawara, Japan; and Dr. Jorge Urban and Oscar Frey in Baja and Mainland Mexico,” said Whale Trust Executive Director Dr. Meagan Jones.

“This study would not have been possible without them. Thank you to all who supported this project and continue to support these independent studies across the Pacific.”

The paper, published in Scientific Reports Volume 9, is available for download at www.nature.com/articles/s41598-019-42233-7.

Whale Trust is a Maui-based non-profit organization whose mission is to promote, support and conduct scientific research on whales and the marine environment, and broadly communicate the findings to the public.

Whale Trust research programs focus on behavior, communication and social organization of whales. Results from Whale Trust field research are the basis for a broader program of outreach and education that involves the public, educators and students. For more information, visit www.whaletrust.org.