Whale's epic journey leads to possible theory about their migration

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Whale's epic journey leads to possible theory about their migration

April 15, 2015 - 21:06
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The critically endangered Western North Pacific gray whales, one of two distinct groups of gray whale may actually be extinct as scientists track individuals swimming to and from Mexico.

Gray Whale breaching (file photo)

Until now, it was believed there were two distinct groups of gray whales: the Eastern gray whale (EGW), found along the west coast of North America, and the critically-endangered Western gray whale (WGW), found along the coast of eastern Asia. US and Russian biologists say a population living only on the western side of the Pacific may now be extinct.

Scientists attached satellite-monitored tags to seven WGWs at their primary feeding ground off Sakhalin Island, Russia. Three of them subsequently migrated to regions occupied by the non-endangered EGWs.

Longest documented migration

One of these whales was a female named Varvara, and she had the longest-lasting tag. She had visited all three major EGW reproductive areas off Baja California, Mexico, before returning to Sakhalin Island the following spring. Her 22,511 km round-trip is the longest documented mammal migration and strongly suggests that some presumed WGWs are actually EGWs foraging in areas historically attributed to WGWs.

One, not two populations

The finding that three of seven whales tagged off Russia crossed the North Pacific to breeding grounds off Mexico, suggests they may be part of the same population.

"These whales were almost certainly born in Mexico (the eastern North Pacific)," lead researcher Prof Bruce Mate of Oregon State University Marine Mammal Institute told the BBC. "If this small sample size is typical, it would suggest that [the two populations are one].

Russia's oil exploration threatens gray whales

The gray whale is found mainly in shallow coastal waters of the North Pacific Ocean. While the Eastern population has recovered to around 20,000, the number of Western gray whales remain very low with only around 180 individuals left, according to the International Whaling Commission. The scientists there have raised concerns about the threat of oil exploration in eastern Russia to gray whales in the area.

Russia says it is aware of the problem, but the company's capacity to shift is limited for financial reasons. Western Pacific gray whales (also known as grey whales) come to Sakhalin each summer to feed, and seismic survey work—which involves producing high-intensity sound pulses and studying reflections from rock strata under the seafloor—can seriously disrupt their feeding. The small area where the whales congregate has shallow water, and scientists suspect this is where mothers teach their calves how to feed at the seafloor.

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