Scientists from Hawaii have reported what’s believed to be the first humpback whale calls ever recorded in the middle of the ocean between Hawaii and Mexico.

“It really is amazing,” said marine biologist Beth Goodwin of the Jupiter Research Foundation, co-author of a paper that describes the whale songs.

The findings, published in the Journal of the Acoustical Society of America, offer intriguing questions about the North Pacific population of humpback whales, including the current National Marine Fisheries Service position that describes the subset groups that breed in the winter off Hawaii and off Mexico’s west coast as distinct populations deserving of separate status and management.

Scientists with the Jupiter Research Foundation and Maui’s Whale Trust last year launched an unmanned surface vehicle on a 4,000-mile journey into the Pacific, recording, among other things, the humpback whale calls at midocean during the 100-day survey.

“I thought there was a chance, but not a very strong chance, of hearing them,” Goodwin said. “It was a needle in a haystack. Fortunately, the needle was a loud one.”

The Wave Glider — a surfboard-size surface platform tethered to a 26-foot submerged submarine — was controlled from Puako, Hawaii island, by Goodwin and her team.

The controllers not only monitored the craft and made course alterations when necessary, but downloaded photographs and short samples of recordings via satellite.

From Jan. 16 to April 25, 2018, the craft followed a path from Hawaii toward Mexico, completing 2,272 hours of recordings with more than 4,000 cetacean calls, which include whales, dolphins and porpoises. Of these calls, 2,048 were identified as humpback whale calls.

The humpback calls were recorded up to 1,357 miles offshore in late January and February. On many days multiple humpback calls were heard, including up to 377 calls over 23 hours one day.

But Goodwin said determining how many whales were out there remains unknown, because one whale can make many calls.

According to lead author Jim Darling of Whale Trust, the findings suggest a number of possibilities, including a previously unknown migration route to Hawaii, travel between Mexico and Hawaii groups within the same season, or even a separate offshore population of humpback whales.

Goodwin said it’s possible the open ocean is another destination for humpback breeding.

“Other species do it in deep water,” she said. “Maybe the humpbacks do it, too. We don’t really know.”

At the very least the results suggest a widening of the winter distribution and habitat of humpbacks, Goodwin said, and it might also be true that these offshore whales are not represented in current population estimates.

The National Marine Fisheries Service describes 14 distinct populations of humpback whales worldwide. They include the Hawaii population, which breeds in the main Hawaiian Islands during the winter and feeds in Alaska and northern British Columbia during the summer, and the Mexican population, which breeds in the winter along the Pacific coast of Mexico and feeds in the summer across a broad range from California to Alaska.

A growing Hawaii population, with some estimates as high as 10,000, was recently taken off the list of species protected by the Endangered Species Act, while the Mexican population remains listed as threatened.

Findings from the latest study further question the independence of the Mexico and Hawaii humpback whale populations, the scientists said.

In a study published in May, Darling concluded that a convergence of humpback songs suggests an ongoing but annually variable mixing of populations throughout the North Pacific.

What’s more, plenty of photo-identified individual whales have been documented in both breeding grounds.

The latest study underscores the need for further investigation into the open-ocean whales, Goodwin said, and the use of autonomous ocean-going vehicles, such as the Wave Glider from Liquid Robotics Inc., seem well suited to help tackle the issue.

Goodwin said the study’s results come from what she described as the first leg of Jupiter’s Wave Rider HUMPACS (Humpback Pacific Survey) acoustic survey. While the first leg sent the unmanned craft east last year, it was sent westward this year. Findings from that survey have yet to be released.