North Pacific Humpback Whales Can Be Grouped Into 5 Distinct Populations, According To New Genetic Study

By Ajit Jha on December 4, 2013 9:14 AM EST

Humpback whale breaching in "Marino Ballena National Park", Costa Rica
A new study argues that there are actually 5 distinct populations of North Pacific humpback whales. The whale shown here, breaching in Marino Ballena National Park in Costa Rica, is likely part of the Central America branch. (Photo: Shutterstock)

There are five distinct populations of humpback whales in the North Pacific Ocean, according to the first comprehensive genetic study of its kind. In addition, the study has also recommended that North Pacific humpbacks be considered as a single "distinct population segment" under the Endangered Species Act. The study, which was supported by the National Fisheries and Wildlife Foundation, the Office of Naval Research, and the Marine Mammal Endowment at Oregon State University, will be published in the journal Marine Ecology - Progress Series.

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First assigned the Latin name of Megaptera novaeangliae by the German naturalist Georg Borowski in 1781, the humpback whale is today facing conservation issues primarily because of commercial whaling. The whalers in the 20th century killed more than 200,000 humpbacks. In North Pacific, some 25,000 have been killed. Humpback whales, earlier listed as endangered under the Endangered Species Act in the United States is now downlisted by the International Union for the Conservation of Nature (IUCN) on a global level. The IUCN, however, added two population segments recently among the endangered including one in the Sea of Arabia, and the other in Oceania. It is quite likely that one or more of the newly identified populations in the North Pacific could be considered endangered, said Scott Baker, associate director of the Marine Mammal Institute at Oregon State University's Hatfield Marine Science Center and lead author on the paper, in a press release

In the three year International study, known as SPLASH (Structure of Populations, Levels of Abundance and Status of Humpbacks), scientists studied nearly 2,200 tissue biopsy samples. The scientists collected the tissue samples from humpback whales in 10 feeding regions and eight winter breeding regions. The genetic differences and migratory connections between breeding and feeding grounds could be studied as scientists used sequences of mitochondrial DNA and DNA profiles for analysis. North Pacific humpback whales could be a subspecies, at an oceanbasin level, of Humpback whales, ubiquitous across all oceans, according to  Baker. His claim was based on "genetic isolation of these populations on an evolutionary time scale."

Baker also claimed that there are multiple distinct populations within the North Pacific subspecies, as the study showed. However, "They differ based on geographic distribution and with genetic differentiations as well, and they have strong fidelity to their own breeding and feeding areas," Baker said.

The five populations the study identified are:

  1. Okinawa and the Philippines
  2. a second West Pacific population with unknown breeding grounds
  3. Hawai
  4. Mexico
  5. Central America 

There are, however, nuances within the five populations, according to Baker. "The Mexico population, for example, has 'discrete' subpopulations off the mainland and near the Revillagigedo Islands, but because their genetic differentiation is not that strong, these are not considered 'distinct' populations," he said.

In order to estimate humpback whale populations, the SPLASH program made use of photo identification records. There are about 22,000 humpbacks in the North Pacific, according to the researchers. This is about the same number on record from before whaling decimated their numbers. The recovery efforts have been broadly successful with variable records among diverse population groups. 

The history of exploitation and recovery is unique to each of the five distinct populations, according to Baker. Whale populations within oceans, unlike terrestrial species, are not isolated by geographic barriers. Feeding and breeding areas, as well as migration routes, are passed down from mother to calf and from one generation to the next. The fidelity to migratory destinations, according to Baker is cultural, not genetic. This culture differentiates whales leading eventually to "genetic differentiation — and ultimately, the five distinct populations identified in the North Pacific," Baker said.  

Picture above courtesy of Shutterstock.

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