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Results of first leg of Wave Glider Humpback Pacific Survey published

By Staff | Jul 11, 2019

An autonomous (robotic) Wave Glider Mission from Hawaii to Mexico detected humpback whale calls in the tropical mid-ocean, raising questions about the definition of the whales’ winter breeding assemblies. This image has been altered to include the Wave Glider. PHOTO BY ED LYMAN-HIHWNMS-NOAA FISHERIES PERMIT #782-1719.

Jupiter Research Foundation and Whale Trust of Maui last week announced the publication of the results of the first leg of their autonomous Wave Glider HUMPACS (Humpback Pacific Survey) acoustic survey in the Journal of the Acoustic Society of America-Express Letters.

During a 100-day, nearly 7,000-kilometer (3,800-nautical-mile) round-trip survey on a line between Hawaii and Mexico within the 2018 winter breeding season, humpback whale calls were heard in the mid-ocean basin, halfway between the known near-shore assemblies.

“They’re not ‘supposed’ to be there,” said Dr. Jim Darling, Whale Trust biologist and project partner.

Humpbacks are known to assemble in specific near-shore, relatively shallow breeding grounds in Mexico and Hawaii. “But then no one has looked in these more remote, offshore areas either,” Darling added.

Mission control was from Puako, Hawaii, where Beth Goodwin, Jupiter Research Foundation vice president and HUMPACS project manager, and her team were in daily communication with the Wave Glider, monitoring status, downloading surface and underwater photographs, downloading short samples of recordings via satellite and making course alterations if needed.

From Jan. 16 to April 25, 2018, the Wave Glider, named Europa (after one of Jupiter’s moons), performed a 6,965.5-kilometer, 100-day continual acoustic survey from Hawaii toward Mexico circa 20 degrees north.

The survey resulted in 2,272 hours of recordings and included over 4,000 cetacean calls. Of these calls, 2,048 were identified as humpback whale calls.

The humpback calls were recorded up to 2,184 kilometers (1179 nautical miles) offshore spanning 30 days between Jan. 20, when the Wave Glider left Hawaii, to Feb. 23, 2018.

On many days, multiple humpback call detections were recorded (up to 377 calls over 23 hours of a day). Actual numbers of whales cannot be determined, as one whale can make many calls.

“This was risky – we had no idea if humpbacks were even out there,” said Goodwin. “And then, even if they were, there were needle-in-haystack odds of intersecting them considering the size of the Wave Glider and the size of the ocean.”

Possible explanations, suggests Darling, include an undocumented migration route to Hawaii, a separate (from Hawaii and Mexico) offshore assembly of humpback whales, or travel between Mexico and Hawaii assemblies within the same season.

At the very least, these results indicate an extension of winter distribution and habitat of humpbacks. It could also be that these offshore whales have not been included in current population estimates.

Since 2016, the model used by the U.S. National Marine Fisheries Service to manage humpback whale populations has treated the Mexico and Hawaii winter assemblies of humpback whales as distinct populations. As such, these populations have different status under the U.S. Endangered Species Act (ESA). Mexico humpback whales are considered threatened, while Hawaii humpback whales have been delisted (the Hawaii population has no protection under the ESA).

This assessment is further complicated by longstanding research showing shared song between the breeding assemblies and an interchange of photo-identified individual whales between these two winter breeding grounds.

The findings question the independence of Mexico and Hawaii humpback whale populations and illustrate the huge potential for the use of autonomous vehicles in the study of whales across remote locations of the ocean.

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

The paper is online at doi.org/10.1121/1.5111970.