Between May and July of 2013, a single grey whale (Eschrichtius robustus) was spotted off the coast of Namibia. This was odd, as while there have been rare sightings of this species in the Atlantic Ocean, they are usually confined to the northern hemisphere.
It turns out the animal had travelled at least 20,000 kilometres – halfway around the planet – setting a record for a migration of any mammal, barring humans.
Rus Hoelzel at Durham University in the UK and his colleagues used tissue samples collected from the whale’s skin and analysed its DNA to trace its origins.
By comparing it with other grey whale populations, they found that this individual, a male, was probably born to the endangered western North Pacific population, found along the coast of eastern Asia. This means it travelled at least 20,000 kilometres to get to the southern Atlantic. Earth’s circumference is slightly over 40,000 kilometres.
“This is the record really for an in-water migration, if you’re assuming that this individual started its life in the north-west Pacific and it found its way to Namibia,” says Hoelzel. “That’s as far as any vertebrate has ever gone in water, as far as we know.” Land dwelling mammals fall far short of this feat – the record is a grey wolf that roamed more than 7000 kilometres in a year.
While it is impossible to know for sure how this whale got to the southern Atlantic, the team has proposed three possible routes – it could have headed north through the Arctic, south around South America, or along Asia and around Africa.
“At the population level, what’s interesting is that we are seeing a lot of changes in the environment that have to do, in this particular case, with the opening up of the Arctic Ocean due to climate,” says Daniel Palacios at Oregon State University. “It goes beyond this one animal to potentially many animals doing the same thing.”
Journal reference: Biology Letters, DOI: 10.1098/rsbl.2021.0136
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