A gray whale has swam the longest distance ever recorded in marine vertebrates – more than 16,700 miles – halfway around the world.
The male whale, spotted off Namibia in 2013, is the first gray whale ever recorded in the Southern Hemisphere.
But it took several years of genetic research to confirm the whale’s origins in the North Pacific, according to a study published today in the journal. Biology Letters.
There are two known groups of gray whales: the eastern gray whales, whose numbers remain stable, with around 20,500 individuals, and the endangered western gray whales, with an estimated 200 individuals remaining in the wild, mostly due to decades of commercial whaling. Eastern grays migrate from the seas around Alaska and Russia to the breeding grounds of Baja California. Little is known about the western gray whale’s breeding grounds, but they have been recorded as feeding throughout eastern Russia.
When study co-author Simon Elwin, a zoologist at Stellenbosch University in South Africa, first heard about the 2013 sighting, he said, “I was a bit dismissive.” “It’s like someone saying they saw a polar bear in Paris – technically they can get there, but it doesn’t look very realistic.”
The images confirmed that it was indeed a gray whale about 40 feet long. The animal stayed at Walvis Bay for two months, possibly because it was malnourished, which allowed Elwin and Tess Gridley, also a zoologist at Stellenbosch University, to collect minimally invasive DNA samples. (See gray whale photos on Walvisbay.)
The gray whale’s astonishing feat – beating out the previous record holder, a leatherback turtle tracked 12,774 miles across the Pacific Ocean – also left scientists wondering: That is, why does the gray whale go so far from its home?
The authors speculate that the rapid decline in Arctic sea ice due to climate change may allow gray whales to explore – or get lost – in new habitats, although there is not enough data to draw any conclusions.
For a whale that usually migrates 5,000 miles, “Travel is too expensive [so] Co-author Ross Holzel, an evolutionary biologist at Durham University in the UK and a National Geographic explorer, says. “It makes you wonder why they do it, and under what circumstances? For these reasons, it is scientifically interesting.”
For their research, Gridley and Elwen teamed up with Hoelzel and Durham University evolutionary biologist Fatih Sarigol to compare whale genomes with other gray whale genomes stored at the US National Center for Biotechnology Information, a digital repository of the genomes of more than a thousand organisms.
They wanted to rule out the possibility that the whale was from an unknown group of inhabitants of the Atlantic Ocean; There is fossil evidence of gray whales in the Atlantic Ocean, and two Gray whales have been seen in the North Atlantic and Mediterranean in recent years.
“There are species of cetaceans that we know very little about because they are very difficult to encounter,” Holzel says. “But in the case of the gray whale, they tend to be coastal and somewhat recognizable, so the idea of such a hidden group in the Atlantic is probably not very likely.”