In May 2013 marine biologists were stunned by the news of the first ever sighting of a grey whale south of the equator, just off the coast of Namibia in Walvis Bay.
Could this whale reflect a remnant of an Atlantic population long thought to be extinct – the last sighting by whalers apparently in the 1740s – or the start of a new population there?
Now a team of researchers from Durham University in the United Kingdom and Stellenbosch University in South Africa, have conclusively identified the lone male grey whale’s birthplace as the North Pacific. Their findings were published in the journal Biology Letters today (9 June 2021).
While grey whales are well known for performing the world’s longest migrations, this Namibian grey whale broke every record in the book, travelling an estimated 27 000 kilometres from his place of birth – nearly halfway around the world.
Prof Rus Hoelzel, an evolutionary biologist from Durham University and main author, sequenced the whale’s full genome in order to meet the challenge of identifying its origin: “This unequivocally identified his birthplace as the North Pacific. What we don’t know, however, is whether this remarkable long migration is just accidental vagrancy, or whether its presence in the Atlantic represents a foraging excursion, permitted by passage through the Arctic pack ice.”
Grey whales were hunted to near extinction off Korea and Japan early in the 19th century, but the eastern Pacific population was never as severely affected. In the Atlantic, the history is less clear, though there are records dating back to the late Pleistocene, he adds
Co-author and bioinformatician Fatih Sarigol, also from the UK, says ideally they would have preferred to work with more than one sample, or to document such a migration with a GPS tracker: “No one could have expected this whale to visit the South Atlantic. For such unexpected cases in science, we had to use extraordinary methods to investigate its origin,” he explains.
Dr Simon Elwen and Dr Tess Gridley, directors of the Namibia Dolphin Project and research associates in the Department of Botany and Zoology at Stellenbosch University, witnessed this unique sighting back in 2013: “During the two months the whale stayed in Walvis Bay, we collected as much information as possible. This included the genetic samples now used in the analysis. We also took detailed photographs, as grey whales can be identified through their markings.”
They knew the genetic sample would help them to determine which stock the whale came from, and how far it might have travelled. So far the photo-identification of the grey whale has not (yet) produced a match.
According to the researchers, this sighting in the South Atlantic, combined with a handful of other sightings in the North Atlantic over the past decade, indicate the species is on the move.
Migration of grey whales from the Pacific Ocean stocks may also be attributed to human activities: “We believe the most likely travel route for the Namibian whale was via the Arctic, a passage only made possible due to the receding ice flows attributed to climate change in recent years,” they conclude.
- The article, “Natal origin of Namibian grey whale implies new distance record for in-water migration”, was published in Biology Letters on 9 June 2021. It is available online at https://royalsocietypublishing.org/journal/rsbl
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