A new study shows the number of humpback whales in the Northern Pacific has grown dramatically to more than 18,000, a finding likely to spark new debate about the whales' status as an endangered species, according to Hawai'i whale experts.

The study sponsored by the National Oceanic and Atmospheric Administration is the most comprehensive study ever of any large whale population, according to David Mattila, science coordinator for the Hawaiian Islands Humpback Whale National Marine Sanctuary.

The Northern Pacific population was fewer than 1,500 in 1966 when international hunting of humpbacks was banned. At least half of the North Pacific humpbacks migrate between summers near Alaska and winters around Hawai'i.

Jeff Walters, co-manager of the Hawaiian sanctuary, said the study findings fit well with what scientists have observed here.

"It's not a complete success, but it's definitely very encouraging in terms of the recovery of the species," he said. However, the growth in whale population here "creates a whole new set of wildlife management issues or challenges."

The number of whale-boat collisions in Hawaiian waters has been increasing, which Walters said is probably because the population is larger, and also because more people report the incidents. Whale entanglements in marine debris, fishing gear and aquaculture structures are also a growing concern.

"You have more whales, and more ocean uses," he said. "It does create new challenges or increased challenges for us to try to find that peaceful coexistence where we can all get along out there when there's more people and more whales out in the water."

Walters predicted there will be discussion in the scientific community and state and federal agencies about whether it is appropriate for the whales to be "downlisted" from an endangered species to a threatened species. Providing hard data to help answer that question was one of the aims of the study, he said.

The whales are protected under federal laws that include the Marine Mammal Protection Act and the Endangered Species Act.

"I think those discussions are bound to happen, and we knew that going into the study, we anticipated it," said Naomi McIntosh, superintendent for the humpback sanctuary. However, the study raises new questions about the mammals, and "I think it's too early to make that call," she said.

LOCATION MATTERS

While the overall population in the Northern Pacific is estimated at 18,000 to 20,000, the study shows there are differences in how well the whale populations are doing in different areas of the Pacific.

Some seem to be growing in numbers, including the Central Pacific population that arrives in Hawai'i each year. But populations in other areas, including at least one subgroup in the Western Pacific, do not appear to have fared as well.

Another concern is that the data could be "misinterpreted" to support a resumption of whaling.

"I think there is some concern that this data would be used by pro-whaling nations to support their argument that it's OK to start harvesting humpbacks," Walters said.

The survey is called Splash — for Structure of Populations, Levels of Abundance and Status of Humpbacks — and is an international effort involving more than 50 organizations and more than 400 whale researchers in the Pacific.

The study used a system of photographing whale flukes of the populations in six different feeding and breeding areas around the world, and then matching the pictures with whale flukes photographed in wintering areas.

Cascadia Research in Olympia, Wash., used a library of 18,000 photographs of whale flukes to identify 8,000 individual whales, allowing researchers to track the movements of individual whales and estimate the sizes of the mostly separate whale populations in various parts of the Northern Pacific.

Researchers who worked on the study collected thousands of photographs documenting scarring from line entanglement and ship strikes, and will use that information to analyze how those incidents vary among the Pacific regions.

More than 6,000 biopsy samples were also collected for future studies of genetics and pollutants.