New research suggests a possible undocumented whale migration route between Hawaii and Mexico and raises questions about whether whales require shallow nearshore waters for breeding and if the Hawaii and Mexico humpbacks are really separate groups.

“They’re not ‘supposed’ to be there,” said Jim Darling, co-founder of Whale Trust and project partner in the 2018 study, in a news release July 1. “But then no one has looked in these more remote, offshore areas either.”

Darling, with project manager Beth Goodwin, Maya Goodoni, Adam Taufmann and Murray Taylor of the Jupiter Research Foundation, published the results in the Journal of the Acoustic Society of America – Express Letters of the first robotic HUMPACS (Humpback Pacific Survey) acoustic survey from a 100-day round trip between Hawaii and Mexico.

“The purpose of the study was to determine if humpback whales were present in offshore tropical waters in the winter breeding season in addition to their traditional nearshore assemblies,” according to the study published June 20.

For some background, the U.S. National Marine Fisheries Service has treated the Mexico and Hawaii winter groups of humpback whales as two distinct populations. Mexico humpback whales are considered threatened under the U.S. Endangered Species Act, while Hawaii humpback whales have been delisted.

However, the study investigates a potential connection between the winter breeding assemblies by using an autonomous Wave Glider, an underwater vehicle produced by Liquid Robotics, a Boeing company.

From Jan. 15 to April 25, 2018, the Wave Glider, named Europa, collected around 2,272 hours of recordings that included over 4,000 cetacean calls from humpback whales, minke whales and unidentified cetaceans. About 2,048 of those calls were identified as humpback whales. The number of calls does not represent the number of whales, the study said.

The surfboard-sized machine traveled 4,328 miles, monitoring status, downloading surface and underwater photographs, and collecting samples of recordings via satellite. The Wave Glider can be submerged up to 26 feet.

Goodwin and her team communicated daily with the Wave Glider, studying humpback whale behavior in far less explored areas, such as in “deep ocean basins.”

“To our knowledge, humpback whales have not been previously reported in these mid-ocean tropical latitudes between Mexico and Hawaii winter assemblies,” the study said.

Humpbacks are known to assemble in specific nearshore, relatively shallow breeding grounds in Mexico and Hawaii, Darling said.

And while there were a considerable amount of humpback whale calls during the beginning of the survey (Jan. 20 to Feb. 4) around the halfway point to Mexico, the return trip had no reported humpback whale calls in the same locations.

Additionally, only fragments of songs were recorded during that period, which can be due to the Wave Glider hearing a “combination of distance and noise” or that the whales were actually just “uttering components” of the usual full cyclical song.

Overall, the study suggests that the Wave Glider may have intersected an undocumented migration route from northern feeding grounds to Hawaii. It also may have identified a separate offshore group of humpbacks and travel between Mexico and Hawaii assemblies in the same season.

The presence of humpback whales in tropical mid-ocean areas during the breeding season also reflects possible “atypical behavior,” meaning the Wave Glider detected a small population of whales doing something different than other whales.

The study also mentions the possibility of an offshore assembly of humpback whales, compared to the usual nearshore assembly by Mexico or Hawaii.

“All humpback winter assemblies globally are characterized by shallow banks relative to surrounding deep seas and a sea water temperature range,” according to the study. “Europa’s route met the temperature characteristics (of 70 to 81 degrees), so the question which arises in this explanation is on the necessity of shallow water to humpback whale breeding activities.”

These results indicate that these offshore humpback whales have not been included in current population estimates. The team also concluded that it may show an extension of whale habitats.

“We feel certain our results will encourage more research, affect how humpback and other whales are monitored, and help with management,” Goodwin said in the news release.

For more information about the Whale Trust or the Jupiter Foundation, go to whaletrust.org/ or jupiterfoundation.org/.

* Dakota Grossman can be reached at dgrossman@mauinews.com.