Using genetic samples, collected from free-swimming humpback whales with a small biopsy dart, scientists have been able to look at two types of DNA; Mitochondrial DNA which is inherited from the mother, and nuclear DNA which is inherited from both parents.
Researchers from the British Antarctic Survey found that although female humpback whales have crossed from one hemisphere to another at certain times in the last few thousand years, they generally stay in their ocean of birth.
This isolation means they have been evolving semi-independently for a long time, so the humpbacks in the three global ocean basins should be classified as separate subspecies. This has implications for how we think about their conservation and recovery on a regional scale.
“The colour of the bodies and undersides of the tail (the ‘flukes’) of humpback whales in the northern oceans tend to be much darker than those in the Southern Hemisphere.
Until this study we didn’t realise that these kinds of subtle differences are actually a sign of long-term isolation between humpback populations in the three global ocean basins, " says lead author, Dr Jennifer Jackson of the British Antarctic Survey.
Despite seasonal migrations of more than 16,000 km return, humpback whale populations are actually more isolated from one another than we thought. Their populations appear separated by warm equatorial waters that they rarely cross.
—Dr Jennifer Jackson of the British Antarctic Survey.
“Further genetic sequencing and analysis should also help us to understand more about the pattern of humpback migrations in the past. Big changes in the ocean can leave signatures in the genetic code of marine species. For example, the last glacial maximum caused many to shift southwards until the ice retreated or to find ice-free areas in the north.
Humpbacks are excellent oceanographers; they go where the food is and can travel long distances to get it, so their patterns of past migration can tell us a lot about the ocean thousands of years ago.”