Genetic study supports naming Arabian Sea humpbacks as a distinct subspecies

A new genetic study says humpback whales in the Arabian Sea have evolved separately from the species’ other populations, including the North Pacific humpbacks that migrate to Maui waters each winter.

Researchers say the findings support recognizing the Arabian Sea population as a fourth humpback subspecies, Megaptera novaeangliae indica. The study was published in Frontiers in Marine Science.

The Wildlife Conservation Society led the work with the Environment Society of Oman, the Environment Authority of Oman and other partners. The team analyzed mitochondrial DNA from 2,285 humpback whales sampled worldwide.

The results showed high genetic differentiation between the Arabian Sea whales and the three recognized subspecies in the North Atlantic, North Pacific and Southern Hemisphere, according to the researchers. They said this indicates very limited gene flow between the groups. The Arabian Sea whales also had the lowest genetic diversity of any region studied.

The researchers estimated that the Arabian Sea lineages diverged between about 43,000 and 113,000 years ago.

Formal recognition of a marine mammal subspecies rests with the Society for Marine Mammalogy’s Taxonomy Committee.

“The results clearly indicate the Arabian humpback whales have followed their own evolutionary trajectory for tens of thousands of years,” said Rita Amaral, Ph.D., the study’s lead author, who coordinated the genetic analysis.

The Arabian Sea whales differ from other humpbacks in several ways, according to the study. They do not make long seasonal migrations between polar feeding grounds and tropical breeding grounds, as North Pacific humpbacks do when they travel to Hawaiian waters in winter months. Instead, the Arabian Sea whales stay in tropical and subtropical waters year-round, follow a Northern Hemisphere breeding cycle and sing a song heard nowhere else. Researchers describe them as the only known humpback population that both feeds and breeds in the same area.

The team also analyzed ancient DNA from the specimen used to describe Megaptera indica in 1883. The whale was collected near Basra, Iraq, and remnants are held by the Muséum National d’Histoire naturelle in Paris. The researchers said the analyses confirmed it was a humpback closely related to today’s Arabian Sea whales.

The study describes the population as small, with no sign of growth in the past two decades. It lists threats including entanglement in fishing gear, vessel strikes, underwater noise, pollution and disease. Changes to monsoons and ocean upwelling linked to climate could also affect the sardines and other prey the whales depend on, the paper says. The authors warn the whales could disappear from the region without coordinated efforts to manage those threats.

The International Whaling Commission recognizes the Arabian Sea whales as a discrete population and has recommended a Conservation Management Plan. Aida Al Jabri of Oman’s Environment Authority said the country is exploring stronger habitat protections, including designation of Particularly Sensitive Sea Areas through the International Maritime Organization.

Suaad Al Harthi, executive director of the Environment Society of Oman and a study co-author, said the findings build on more than 25 years of research in Oman, which began with small-boat surveys and now includes satellite tracking and acoustic monitoring.

The International Whaling Commission funded the analyses. The US Marine Mammal Commission funded sampling of the Paris museum specimen.