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California Blue Whales On The Rebound, Study Says

ARUN RATH, HOST:

So we've covered death and destruction around the world, domestic violence at home, but stay with us - we have some good news to report. Blue whales once considered threatened with extinction are now doing very well off the coast of California. That's according to a recent study out of the University of Washington co-authored by Trevor Branch.

TREVOR BRANCH: What we found was that although whaling knocked them down to fairly low levels, now they've rebounded and they're back at close to their original abundance.

RATH: California blue whales range all the way from Alaska to Costa Rica, but they were devastated by whaling. Now according to the study they're back to 97 percent of their historic levels - about 2,200 whales. The findings were based a complex computer analysis that factored in previous and current populations and potential threats. They also had to figure out how to distinguish the California blue whale population from other blue whales that look exactly the same.

BRANCH: The key piece of information was to use their songs these blue whales make, which are unique to the two populations, to separate out where the populations live and from that to separate out the catches.

(SOUNDBITE OF WHALE SONG)

RATH: So you can tell which whales come from where based on their regional accents?

BRANCH: Exactly or maybe a slightly separate language, depends on how you word it. From that you can piece out who's making the calls. Does it sound like an East population or does it sound like a Western population?

RATH: Now since the study was published some scientists have questioned whether it maybe paints too bright of a picture that, for example, whaling fleets always underreport their catches so there could actually be a greater threat from commercial fishing. What's your response to that?

BRANCH: We looked at a lot of different - what do we call - sensitivities. So you can run the model in different ways and see how much of a difference it makes. Even if you add 20 percent to the catchers that we have in the model, we still say that the population is more than 90 percent of what was there before whaling.

RATH: Now you were looking specifically at the population of California blue whales. Is there anything that we know about how blue whales across the world are doing or whales in general? Does this reflect a broader recovery?

BRANCH: Sadly, they don't reflect a broader recovery in blue whales. This is the bright spot as it were. Globally there are still pretty low levels, it's probably somewhere between five and 10 percent of what used to be there. In some places it's really, really bad. So in the Antarctic we caught 99.85 percent of the Antarctic blue whales before we stopped whaling. Whereas off the west coast of the U.S. they just weren't making enough money to keep on whaling.

RATH: With this population of California blue whales was this a case of nature just basically being left to recover on its own? Or was there a stronger conservation push here?

BRANCH: The key here was we stopped whaling and the whaling was at such levels, I mean, some years they were catching more than 20 percent of the entire population in a single year. There is one more factor which is that currently we are killing blue whales. We're not whaling them, but we're hitting them with ships and the ships are a thousand times bigger than a blue whale and so there are lots of people trying to reduce the number of deaths from ship strikes and all these efforts I think have paid off, you know, it's a conservation success story.

RATH: Trevor Branch is an assistant professor in aquatic and fishery sciences at the University of Washington. He's co-author of a study on the resurgence of California blue whales. Trevor, thanks for your time.

BRANCH: Thank you very much. Transcript provided by NPR, Copyright NPR.

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