May 18, 2009

Blue whales are returning to Alaska waters in search of food and could be re-establishing an old migration route decades after they were nearly wiped out by commercial whalers.

The endangered whales, believed to be the largest animals ever to live on Earth, have yet to recover from the worldwide slaughter that eliminated 99 percent of their number, according to the American Cetacean Society. The hunting peaked in 1931 with more than 29,000 animals killed in one season.

The animals used to cruise from Mexico and Southern California to Alaska, but they had mostly vanished from Alaska waters.

However, several sightings of California whales in recent years off the coasts of Alaska and British Columbia suggest the massive mammals are expanding north again in search of tiny shrimp-like krill to eat.

Blue whales can grow up to 100 feet long and typically eat 4 tons of krill a day during the summer.

Researchers got an inkling of the trend in 2004 during a humpback whale survey in the Gulf of Alaska. In total, six whales were spotted in Alaska waters in 2004. Three were in the Aleutian Islands. Those belonged to the western Pacific group nearer to Russia.

Researchers compared photographs of the six whales with those in a photo identification catalog dating back to the mid-1980s. Positive matches were made by looking at the distinctive pigmentation of the skin on the whale's back and the shape of its dorsal fin.

One of the Gulf of Alaska whales matched a California whale. That whale had been seen five times in 1995 and 1998 near the Santa Barbara Channel off southern California.

After the 2004 sightings, one or two blue whales were spotted each year off British Columbia in 2005 and 2006. In 2007, researchers spotted five in one day, including a mother and calf, near the Queen Charlotte Islands off British Columbia. Three more were spotted the next day. There previously had been only a couple of blue whale sightings in that area in 50 years.

Researchers eventually documented 15 blue whales off the coast of British Columbia and in the Gulf of Alaska that they believe are part of the California group of about 2,000 animals. Four were matched with photos in the catalog.

Scientists say, "We speculate that this represents the re-establishment of a traditional migration pattern for an eastern North Pacific blue whale population,"

Scientists aren't certain why blue whales are beginning to migrate again to the north. One theory is that ocean conditions have changed and pushed krill farther north. The changes are believed to be part of a normal shift in ocean temperature that occurs every decade or so.

There were an estimated 350,000 blue whales before whalers hunted them to near-extinction in the 20th century. The International Whaling Commission banned hunting of blue whales in 1966, but recovery has been slow. According to the American Cetacean Society, there are an estimated 8,000 to 14,000 blue whales. The biggest number is off the California coast.