California blue whales, the largest animals on Earth once driven to near extinction by whaling, have made a remarkable comeback to near historic, 19th-century levels, according to a University of Washington study released on Friday.

 

The recovery makes California blue whales - which study authors say now number about 2,200, or 97 percent of historical levels - the only population of blue whales known to have recovered from whaling.

 

Despite the comeback, the whales - which as adults can reach nearly 100 feet (30 meters) in length and weigh 190 tons (172 tonnes), twice as much as the largest known dinosaur - are still being struck by ships off the California coast at numbers above allowable U.S. limits, according to the study's authors.

 

Conservation groups say at least 11 blue whales are struck each year along the U.S. West Coast, nearly four times the "potential biological removal" level of 3.1 permitted under the U.S. Marine Mammal Protection Act.

 

According to the University of Washington paper and a separate paper published earlier this year, some 3,400 blue whales were caught between 1905 and 1971, a number determined in part by examining once-secret Russian whaling archives.

 

The study's authors say that the population of California blue whales is now growing more slowly, partly due to ship strikes and also because numbers are reaching the habitat limit.