The number of California blue whales has rebounded to near historical levels, according to new research by the University of Washington, and while the number of blue whales struck by ships is likely above allowable U.S. limits, such strikes do not immediately threaten that recovery. 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, the Argentinosaurus. They are an icon of the conservation movement and many people want to minimize harm to them, according to Trevor Branch, UW assistant professor of aquatic and fishery sciences.

"The recovery of California blue whales from whaling demonstrates the ability of blue whale populations to rebuild under careful management and conservation measures," said Cole Monnahan, a UW doctoral student in quantitative ecology and resource management and lead author of a paper on the subject posted online Sept. 5 by the journal Marine Mammal Science. Branch and André Punt, a UW professor of aquatic and fisheries sciences, are co-authors.

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, according to monitoring by other research groups. That's likely 97 percent of the historical level according to the model the co-authors used. That may seem to some a surprisingly low number of whales, Monnahan said, but not when considering how many California blue whales were caught. According to new data Monnahan, Branch and another set of co-authors published earlier this summer in PLOS ONE, approximately 3,400 California blue whales were caught between 1905 and 1971.

"Considering the 3,400 caught in comparison to the 346,000 caught near Antarctica gives an idea how much smaller the population of California blue whales was likely to have been," Branch said.