Five Distinct Humpback Whale Populations Identified in North Pacific

A new comprehensive genetic study of the humpback whale populations in North Pacific region suggests that there are five distinct populations of the mammals in the region. This finding comes just in time when the Endangered Species Act proposal is considering listing the North Pacific humpback whales as a 'distinct population segment.'

The first genetic study of the mammals in the region was supported by the National Fisheries and Wildlife Foundation, the Office of Naval Research, and the Marine Mammal Endowment at Oregon State University.

During the three-year study called SPLASH (Structure of Populations, Levels of Abundance and Status of Humpbacks), the researchers analyzed over 2,200 samples of tissue biopsies that were taken from the humpback whales in10 feeding regions and eight winter breeding regions.

The researchers then analyzed the mitochondrial DNA that is maternally inherited and also microsatellite genotypes (DNA profiles). The study program even made use of the photo identification records in order to estimate the population of the humpback whale. Based on the estimation it was revealed that over 22,000 humpback whales live in the North Pacific region.

Using this data the researchers identified the genetic differences and also summarized the migratory links between both the breeding and feeding regions. The five distinct populations are  identified as coming from  Okinawa and the Philippines; a second West Pacific population with unidentified breeding ground, Hawaii, Mexico and Central America.

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

It is not unclear how the government will respond to the identification of five distinct humpback whale populations proposed by the SPLASH study. But this finding definitely emphasizes on the intricacy of examining and managing the marine mammal on a larger global level.

"Even within these five populations there are nuances," noted Baker, who frequently serves as a member of the scientific committee of the International Whaling Commission. "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."

The humpback whale, a species of the baleen whale, feeds only in summers and is known for its distinctive body shape. Under the Endangered Species Act they have been listed as endangered in the U.S., but  have been removed from the vulnerable list by the IUCN.

Since the five distinct species have a different record of exploitation, these factors need to be considered during the assessment of status. Whales that are found in oceans are not separated by barriers but it is the migration route, breeding and feeding grounds that are passed from mother to calf, that continues for generations.

The finding was reported in the journal Marine Ecology.