Three years ago, it was all so clear and unequivocal.

Gray whales live in the North Pacific. They apparently once also lived in the North Atlantic, but appear to have been driven into extinction no later than the eighteenth century. No gray whale had been seen in the Atlantic basin for close to 300 years.

And then one showed up. In May 2010, a gray whale was spotted off the coast of Israel; two months later, the same whale was seen off Spain.

ANALYSIS: Gray Whale Spotted on Wrong Side of World

ANALYSIS: Lost Gray Whale Surfaces Again in the Mediterranean

OK, so gray whales are almost never seen in the Atlantic basin. But they’ve never been found in the Southern Hemisphere, right.

Welllll ….

On May 4, four tour boats on dolphin-spotting cruises near Namibia’s Walvis Bay spotted an unusual whale. Eight days later, photographs taken by John Paterson of the Albatross Task Force confirmed the improbable: the lone whale was a gray whale – the first one ever recorded south of the equator.

Comparison with photographs of the errant Mediterranean gray from 2010 appeared to confirm that it was not the same whale. And so, as Paterson wrote in a blog post for the Namibian Dolphin Project, “The question is now ‘what is the origin of this whale?’”

ANALYSIS: Gray Whale Recovery Fuels Whale-watching Success

One possibility is that the whale swam south past Baja California, rounded the tip of South America and across the Atlantic. But that seems unlikely: it would require the whale to travel a huge distance against currents, through open ocean, from west to east – none of which gray whales typically do.

More likely is that it arrived off Namibia the same way that the 2010 whale was speculated to have shown up in the Mediterranean: by swimming east along the north coast of Alaska, through the Northwest Passage across the top of Canada, and out into the Atlantic. Once there, it presumably sought to guide itself by keeping the coastline to its left, as it would do on its normal journey from Alaska to Mexico. But whereas the whale in 2010 turned east into the Mediterranean, this one kept swimming south.

Why have there been no records of gray whales in the Atlantic for 300 years, and then two in the last three? One likely explanation lies in the proposed route by which the whales arrived in their unexpected locations. In recent years, the Northwest Passage has undergone increasing amounts of ice melt so that it has become open and navigable to shipping during summer months for five of the past six years. And if ships can find their way through, then whales almost certainly can as well.

ANALYSIS: Arctic Nations Debate Future

The future fate of this particular whale is uncertain, but its prognosis – unless it can somehow find its way back whence it came – is unlikely to be good. But in a world that is changing rapidly due to global warming, the first Southern Hemisphere gray whale may very well not be the last.

IMAGE: Gray whale breaching in Baja California, Mexico. (Christophe Boisvieux/Corbis)