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California blue whales rebound from whaling

In a conservation success story, the number of California blue whales has rebounded to near historical levels after being hunted to near extinction.

Photo credit: J Gilpatrick/M Lynn/NOAA

California blue whales – the cow is 76 feet long and the calf is 47 feet – swim near the California Channel Islands. Photo credit: J Gilpatrick/M Lynn/NOAA

The number of California blue whales has rebounded to near historical levels, according to new research by the University of Washington.

This is the only population of blue whales known to have recovered from whaling – blue whales as a species having been hunted nearly to extinction.

Blue whales – nearly 100 feet in length and weighing 190 tons as adults – are the largest animals on earth. And they are the heaviest ever, weighing more than twice as much as the largest known dinosaur.

California blue whales ­ are at their most visible while at feeding grounds 20 to 30 miles off the California coast, but are actually found along the eastern side of the Pacific Ocean from the equator up into the Gulf of Alaska. Today they number about 2,200. That’s likely 97 percent of the historical level, say the researchers.

The researchers says that while the number of blue whales struck by ships is likely above allowable U.S. limits, such strikes do not immediately threaten that recovery. There are likely at least 11 blue whales struck a year along the U.S. West Coast, other groups have determined, which is above the “potential biological removal” of 3.1 whales per year allowed by the U.S. Marine Mammal Protection Act.

The new findings says there could be an 11-fold increase in vessels before there is a 50 percent chance that the population will drop below what is considered “depleted” by regulators.

Study co-author Trevor Branch said:

Even accepting our results that the current level of ship strikes is not going to cause overall population declines, there is still going to be ongoing concern that we don’t want these whales killed by ships.

Without ship strikes as a big factor holding the population back – and no other readily apparent human-caused reason (although noise, chemical pollution and interactions with fisheries may impact them) – it is likely that the population is growing slowly because whale numbers are reaching the habitat limit, something called the carrying capacity.

Cole Monnahan is lead author of the paper on the subject, posted online September 5 by the journal Marine Mammal Science. Monnahan said:

Our findings aren’t meant to deprive California blue whales of protections that they need going forward. California blue whales are recovering because we took actions to stop catches and start monitoring. If we hadn’t, the population might have been pushed to near extinction – an unfortunate fate suffered by other blue whale populations.

It’s a conservation success story.

Read more from University of Washington

Eleanor Imster

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