6-year grey whale mass die-off declared over as scientists research potential causes


A six-year long grey whale mass die-off has been declared over by scientists who are now researching some of the potential causes.

The “unusual mortality event” was first declared by the National Oceanic and Atmospheric Administration in 2018.

Stephen Raverty, veterinary pathologist and adjunct professor at the University of British, said the mortality event officially ended in late March.

“During this timeframe from 2018 to 2023, the population [of grey whales] actually declined from an estimated 28,000 to 14,000,” Raverty explained. “This was a fairly precipitous drop off and coinciding with that were increased numbers of stranded reported individuals along the coast.”

A PLOS ONE study, which Raverty co-wrote, says more that 600 grey whales were stranded along their 17,000 kilometre migratory path between Mexico and Alaska, including along Vancouver Island’s west coast.

READ MORE: Emaciated, dead grey whales spotted on Vancouver Island coastlines for third year in a row

Raverty told CHEK News scientists conducted postmortem investigations on 60 of the dead whales to determine what caused the die-off.

He said killer whale attacks and vessel strikes were major factors.

“Unfortunately, their migratory course follows a number of shipping lanes and these individuals that presented with these catastrophic injuries tend to focus in Puget Sound, in San Francisco Bay as well as Los Angeles Port,” Raverty said.

The research also found the body conditions of the deceased whales were very poor.

Raverty said a number of the whales had very little fat stores, widespread muscle wasting and low nutrition which could be symptoms of the changing water and ice conditions in the whale’s traditional feeding grounds near Alaska.

“Their prey composition has changed and the nutrient value has declined quite considerably which [researchers] directly relate to climate change,” Raverty explained.

He said fortunately there has been a rebound in population, with some new calves, increasing the population from 14,000 to 18,000 over the last year.

While this is good news, Raverty said more research and work needs to be done to mitigate another major mortality event in the future.

“Better understanding the diet preferences, the stress and reproductive hormones, trying to see how they may be able to facilitate management with some of the vessel interactions in different areas,” He explained.

“There’s a lot that has been learned but certainly considerably more that will be coming forward in the future.”

SEE ALSO: Marine heat wave impacted humpback whale population: study

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