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UW Study: Despite Boat Strikes, California Blue Whales Have Rebounded

A 65-foot-long California blue whale swims off Baja California. This pooulation of blue whales are also known as eastern North Pacific blue whales. They were hunted to the brink of extinction in the 1930s, but UW researchers say they've recovered.

California blue whales have rebounded after decades of commercial whaling.

New research from the University of Washington suggests their numbers are back to where they were before humans started hunting the species. 

Cole Monnahan is getting his Ph.D. in quantitative ecology at the University of Washington. That means he uses applied mathematics to solve environmental problems. He says he stumbled on blue whales as a focus for his thesis work, but it didn’t take long to see the fascination.    

Credit Gilpatrick/Lynn/NOAA
California blue whales swim near the California Channel Islands. The species is the largest known animal. The cow shown here is 76 feet long and the calf is 47 feet.

"They are the largest animal that is alive today and that has ever lived, much larger than the largest dinosaurs," he said. “For me, I think it’s really cool. They’re like this giant animal and yet we know actually relatively little about them. They’re very difficult to study.”

And there was an interesting question to answer regarding the blue whales that live in waters off the west coast, so-called California blue whales: Why has their population stopped growing over the past 20 years? And could it be due to fatal ship strikes that have made headlines in recent decades?

To find out, Monnahan used deep sea recordings of their calls to determine how many California whales are around today. He then plugged that figure into an equation along with other data, such as the numbers caught by whaling in the past and the number of ship strikes taking place today.  

And he found that although blue whales as a species are not doing well worldwide, the California population of about 2,200 has recovered to 97 percent of their historical levels.

And he says the fatal ship strikes that occur every year only have a minimal impact even when they occur in numbers above legal limits. 

“We actually do estimate that they are back where they were before we started whaling. It’s just there’s a natural limitation on the population," he said.

So this is actually a good news story for conservationists. And the flat-lining of the population seems to be a symptom of success; the whales are back at a level that the ecosystem can naturally carry.

Even so, Monnahan says it’s crucial that protections for the endangered species stay in place.

The research is published in the journalMarine Mammal Science.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to