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Blue whales of California are back to historical levels, study finds

A conservation success story? Study finds California blue whale population has rebounded

Good news, whale lovers: A new analysis suggests that there are as many blue whales living off the coast of California as there were before humans started hunting them to near extinction 110 years ago.

Today, there are roughly 2,200 blue whales who range from Mexico in the south to Alaska in the north. In the 1930s, that number was closer to 750.

"For us, this is a great conservation success story," said Cole Monnahan, a doctoral student in ecology and resource management at the University of Washington. "We caught way too many whales from this population, but when we left them alone, they recovered."

"And that is really good news," he added. "That it is possible."

Blue whales are the largest animals in the world. They can weigh up to 330,000 pounds and grow up to 110 feet in length. 

These giants of the ocean are found throughout the world, but for this study, published Friday in Marine Mammal Science, the researchers looked at the relatively small population of whales that live in the eastern North Pacific.

During the height of whaling in the 1930s, this population dropped to between 500 and 1,000 individuals the researchers said. After whaling became illegal in the 1970s, however, their numbers began to bounce back.  By the 1990s, the population had grown to about 2,200, according to research from NOAA scientists, and that is currently where it is today.

To see whether this number represented a complete rebound, the team looked at previously published data of how many California blue whales there are currently, the number of California blue whales that were reportedly killed by whalers in the 20th century (3,400) and how many whales are killed each year by ship strikes (probably around 11). 

After feeding all this information into a mathematical model, they concluded that the number of California blue whales swimming around today is 97% as large it was before 1905.

This analysis could explain why the number of California blue whales leveled off in the early 1990s. 

"Before this study some people thought that number should be going up, but if there were about 2,200 whales to begin with, than that is what the environment can support," Monnahan said.

The analysis also suggests that even if ship strikes increased eleven-fold, the California blue whale population would still not be significantly depleted. 

Not everyone is convinced its time to jump for joy, however. 

Jay Barlow, a NOAA research scientist who studies blue whales, said that to accept the authors' good news conclusion, you also have to accept that there truly were only 3,400 California blue whales killed in the 20th century, because that was an important data point for the analysis.

If more whales were killed during that time, and perhaps not recorded, that would suggest the population may originally have been bigger.

"It all depends on whether you believe the whaling statistics or not," Barlow said. "And my guess is there are more underestimates of whales killed, rather than overestimates."

Even if the data is right however, that would make the California blue whales the only blue whale population in the world to have completely rebounded. In other parts of the world, the situation is much more depressing.

Trevor Branch, an assistant professor of aquatic and fishery sciences at the University of Washington and the senior author of the paper, said the blue whale populations in Chile are at 10% to 20% of historical levels. In Antarctica, where there used to be 240,000 blue whales, the population is at 1% of what it once was -- about the size of the California population.

"They are increasing as fast as they can -- about 10% a year," Branch said, "but at that rate their numbers will double every 10  or 11 years or so, so you can see how it will take many more decades before they get back to where they were."

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