A new study has revealed that humpback whales residing in the Arabian Sea are the most genetically distinct humpbacks in the world. Unlike other humpbacks distinguished by their epic 9,000km migrations, the Arabian Sea population has remained separate from other humpbacks for possibly 70,000 years.

"The epic seasonal migrations of humpbacks elsewhere are well known, so this small, non-migratory population presents a wonderful and intriguing enigma," said study co-author Tim Collins from the WCS. "They also beg many questions: how and why did the population originate, how does it persist, and how do their behaviours differ from other humpback whales?"

Divergence

Upon examining DNA from 47 individual whales, the research team compared the results with existing data sets from humpback whales in both the Southern Hemisphere and the North Pacific. Results indicated the Arabian Sea population is highly distinct; estimates of gene flow and divergence times suggest a Southern Indian Ocean origin but suggest it has been isolated for approximately 70,000 years. The separation may be linked to various glacial episodes in the late Pleistocene Epoch and associated shifts in the strength of the Indian Monsoon.

"We have invested lots of energy working to clarify the population structure of several large whale species around the world," said Dr Howard Rosenbaum, senior author of the study and Director of WCS's Ocean Giants Program. "The levels of genetic differences for Arabian Sea humpback whales are particularly striking; they are the world's most distinct population of humpback whales and might even shed some light on the environmental factors that shape cetacean populations."