As gray whale migration reaches its peak, scientists fear another unexplained die-off

phys.org | 5/6/2019 | Staff
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As California gray whales wind their way south along North America's Pacific coast—from their feeding grounds in the Arctic to their spring destination in the secluded lagoons of Mexico's Baja Peninsula—researchers from Alaska to Mexico are watching, worried about another year of unexplained die-offs.

So far, at least three whales have died on the southbound journey, according to a spokesman at the U.S. National Oceanic and Atmospheric Administration. And there are unconfirmed reports of strandings in Mexico.

Necropsies - Whales - Juvenile - Body - Condition

Necropsies suggest two of the confirmed whales were "thin," while a third, a juvenile, seemed to be of average body condition, said NOAA's Michael Milstein.

Last spring and summer, 215 whales inexplicably washed up along North America's West Coast, suggesting thousands more had also perished but had sunk at sea. Concerned, NOAA called for an investigation in May, bringing together researchers from the Arctic to Mexico to explore the strandings in a uniform, systematic manner.

Protocols - Observations - Necropsies - Scale - Blubber

Protocols for nutritional observations during necropsies were established—providing a numeric scale upon which to assess blubber dryness, body condition and the best angles with which to photograph a beached whale. Regular phone calls and check-ins among geographically scattered scientists were also instituted.

Yet, according to Milstein and scientists involved with the investigation, it's still unclear what caused the 2019 die-off and whether the whales will fare better this year.

Mortality - Event - Cause

A similar "unexplained mortality event" occurred in 2000. No cause was ever determined.

"We really won't know anything until about February or March," said John Calambokidis, a whale researcher at Cascadia Research, a nonprofit in Olympia, Wash. That's when observers in the Baja lagoons will be able to examine the whales' physical condition.

California - Whales - Miles - Year - Summer

California gray whales migrate 5,000 miles every year from their summer feeding grounds in the Arctic to their calving grounds in the lagoons of Mexico's Baja Peninsula, where they typically stay until the end...
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