In 2013, a male gray whale was spotted in Walvis Bay off Namibia, which was odd, as no gray whale had ever been seen in the Southern Hemisphere. Where did he come from?

It took several years of research to determine that the whale originated in the North Pacific and had swum an estimated 16,000 miles, or more than halfway around the world, to reach Namibia. The findings were published recently in a study in the journal Biology Letters.

Why would a whale swim so far? The authors speculate the rapid decline in sea ice in the Arctic due to climate change may be allowing gray whales to explore—or get lost in—new habitats, though there’s not enough data to draw any conclusions.

There are two known populations of gray whales: eastern gray whales, whose numbers are stable, with around 20,500 individuals, and western gray whales, which are endangered, with an estimated 200 individuals left in the wild, mostly due to decades of commercial whaling.

Gray whales are no strangers to swimming great distances. Indeed, gray whales have the longest known migration of any mammal. Typically, eastern gray whales swim 5,000 miles from their feeding grounds off Alaska and Russia to mating grounds off Baja, Mexico and then make the return trip yearly. 

Much less is known about western gray whale breeding grounds, but they’ve been recorded as feeding around eastern Russia.

Study co-author Simon Elwen, a zoologist at the University of Stellenbosch, South Africa with  Tess Gridley, also a University of Stellenbosch zoologist, managed to collect minimally invasive DNA samples from the wandering whale in Walvis Bay. They were then able to compare the sample to other gray whale genomes stored in the U.S. National Center for Biotechnology Information.

It turned out that the Namibian whale’s genes did match with those of North Pacific gray whales stored in the biotechnology database. Surprisingly, the researchers say, the closest fit was with the endangered western population.

Next, the team analyzed possible routes the marine mammal could have taken, considering it most feasible that the animal journeyed around Canada through the Northwest Passage. Other options—such as circumnavigating South America or swimming through the Indian Ocean—are less likely, in part due to lack of reported sightings, and also because gray whales tend to feed in shallow water, making long trips over open ocean more difficult.