Five Distinct Humpback Whale Populations Reported in NW Pacific

A new genetic study of humpback whale populations in the North Pacific Ocean suggests that there are five distinct populations in the region. The find comes at the same time as an Endangered Species Act proposal that seeks to designate the region's humpback whales as a single "distinct population segment."

Researchers from both federal and state organizations spent three years conducting what they dubbed the Structure of Populations, Levels of Abundance and Status of Humpbacks, or SPLASH, study. Nearly 2,200 tissue biopsy samples were collected from humpback whales across 10 known feeding zones and eight breeding regions, allowing the researchers to study the whales' genetic differences and outline migratory connections between feeding and breeding locations.

"Though humpback whales are found in all oceans of the world, the North Pacific humpback whales should probably be considered a sub-species at an ocean-basin level - based on genetic isolation of these populations on an evolutionary time scale," said Scott Baker, associate director of the Marine Mammal Institute at Oregon State University's Hatfield Marine Science Center.

Baker was the lead author of the paper on the SPLASH study published in the journal Marine Ecology.

"Within this North Pacific sub-species, however, our results support the recognition of multiple distinct populations," Baker added. "They differ based on geographic distribution and with genetic differentiations as well, and they have strong fidelity to their own breeding and feeding areas."

While humpback whales are classified as endangered under the US Endangered Species Act, the species was recently downlisted on a global level by the International Union for the Conservation of Nature, which maintains the IUCN Red List of Threatened Species used as a benchmark for assessing the overall health of a species.

For now, it is unclear how the administrative bodies governing the national and international status of North Pacific humpback whales will react to the SPLASH study. But at the very least, Baker said the whole situation "underscores the complexity of studying and managing marine mammals on a global scale."

According to the genetic analysis, the North Pacific humpbacks are identified as coming from one of five regions: Hawaii, Mexico, Central America, Okinawa and the Philippines and one other West Pacific population with unknown breeding grounds.

"Even within these five populations there are nuances," Baker said. "The Mexico population, for example, has 'discrete' sub-populations off the mainland and near the Revillagigedo Islands, but because their genetic differentiation is not that strong, these are not considered 'distinct' populations."

By using photo identification records to estimate the size of humpback populations, Baker and his colleagues contend that the number of of humpbacks in the North Pacific region are approximately what they were at before whaling reduced their numbers - about 22,000.

Even though numbers have rebounded to pre-whaling levels, Baker contends it's important to consider recent revelations in moving forward with species management.

"Each of the five distinct populations has its own history of exploitation and recovery that would need to be part of an assessment of its status," he said. "We think this fidelity to migratory destinations is cultural, not genetic. It is this culture that isolates whales, leading to genetic differentiation - and ultimately, the five distinct populations identified in the North Pacific."