Blue Whales Returning to Pre-Whaling Feeding Grounds

Written by on May 12, 2009 in Marine Life
Blue whale drawing

Blue whale drawing by Georeg

Scientists have documented the first known migration of blue whales from the coast of California to areas off British Columbia and the Gulf of Alaska since the end of commercial whaling in 1965.

Blue whale tail - Courtesy of Bob

Blue whale tail – Courtesy of Bob

In the scientific journal Marine Mammal Science, researchers from Cascadia Research Collective in Washington state, NOAA’s Southwest Fisheries Science Center in California, and Canada’s Department of Fisheries and Oceans identified 15 separate cases where blue whales were seen off British Columbia and the Gulf of Alaska. Four of the whales were identified as animals previously observed off the coast of California, suggesting a re-establishment of a historical migration pattern.

Researchers made this identification by comparing photographs of blue whales taken in the north Pacific Ocean since 1997 with a library of nearly two thousand photographs of blue whales off the West Coast. A positive match was determined based on pigmentation patterns in skin color and shape of the dorsal fin.

There are several other techniques for tracking whales, including following vocalizing whales using passive acoustic arrays, tracking active acoustic or radio devices attached to whales, via satellite location tags or by simply following animals for extended periods. Each method has its own strengths and weaknesses.

Blue whale - Credit: NOAA Fisheries

Blue whale – Credit: NOAA Fisheries

Blue whales were severely depleted during commercial whaling activities during the early 1900’s in the north Pacific and along the West Coast as far south as Baja California. Formerly large populations of blue whales in the north Pacific never rebounded after commercial whaling ended while those animals off southern California have apparently fared much better.

Scientists are still not certain exactly why blue whales are now beginning to migrate from southern California to the north Pacific Ocean although changing ocean conditions may have shifted their primary food source of krill further north.

Blue whales are thought to be the largest animal ever to have existed on earth, at up to 32.9 meters (108 feet) in length and 172 metric tonnes (190 short tons) – the largest known dinosaur of the Mesozoic Era was the Argentinosaurus, which is estimated to have weighed up to 90 tonnes (100 short tons).  Mating starts in late autumn and continues to the end of winter.  Little is known about mating behavior or breeding grounds. Females typically give birth once every two to three years at the start of the winter after a gestation period of ten to twelve months.  Scientists estimate that they can live at least 80 years.

They were nearly hunted to extinction throughout the world and are currently listed as endangered under the U.S. Endangered Species Act and as endangered on the red list of the International Union for the Conservation of Nature. 

Blue Whales were abundant in nearly all the oceans until the beginning of the twentieth century. For over 40 years, they were hunted almost to extinction by whalers until protected by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 Blue Whales worldwide, with the largest population of approximately 2,000 off the US West Coast.  Before whaling, the largest population was in the Antarctic, numbering approximately 239,000 (range 202,000 to 311,000).

Copyright ©  2009 by Marine Science Today, a publication of OceanLines LLC

About the Author

About the Author: Celia is Director of Business Operations for OceanLines LLC and is a frequent contributor to both OceanLines and Marine Science Today. She is a certified diver and her favorite topic is marine biology, especially stories about whales. .

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