The population of California blue whales is believed to have rebounded to a historical level.
Blue whales were nearly hunted to extinction but are now believed to be the only species to have recovered from whaling, the University of Washington reported. The number of blue whales struck by ships is most likely still above U.S. allowable limits, but it does not immediately threaten their recovery.
Blue whales are almost 100 feet long and can weigh up to 190 tons as adults; they are the largest mammals on Earth.
"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.
California blue whales are most visible when in their feeding grounds 20 to 30 miles off the coast. Today there are about 2,200 of them, which is about 97 percent of the historical level.
"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," said Trevor Branch, UW assistant professor of aquatic and fishery sciences.
To make their findings, the researchers looked at numbers from Russian whaling archives that were once classified but have now been released to the public. The team separated the whales by the catches taken from the California population from those whales taken in the western Northern Pacific near Japan and Russia using acoustic calls; regions that were attributed to one call or the other were compared with the data on whaling catches.
The whales' recovery does not mean they are no longer in need of any sort of protection. The researchers believed there are at least 11 blue whales struck each year along the U.S. coast which is above the "potential biological removal" of 3.1 whales per year allowed by the U.S. Marine Mammal Protection Act.
"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," Branch said.
