Picture hungry tourists swarming around an all-you-can-eat buffet. Only the tourists are 100 feet long and weigh almost 200,000 pounds. These are blue whales, the largest animals ever, and they’ve come to feast on some of the tiniest animals on the planet: millions upon millions of tiny shrimplike krill.
The scene is the Farallon Islands, dramatic granite outcrops 27 miles west of the Golden Gate. Perched at the edge of the continental shelf, this is a place where seasonal shifts in ocean currents cause upwelling of cold, nutrient-rich water from the ocean depths. That in turn stimulates the growth of massive blooms of phytoplankton at the water’s surface. These microscopic plankton constitute the base of the oceanic food chain. The plankton are eaten by the krill.
Averaging close to 100 tons, blue whales can consume as much as four tons of krill a day during their summer feeding season. The bounty of krill found in the ocean waters around the Farallon Islands is actually able to support that astounding level of consumption by a population of blue whales that visit here during the summer and early fall in the years when upwelling occurs.
That’s when whale-watching cruises to the Farallon Islands regularly spot feeding blue whales and their acrobatic cousins, the humpbacks, as well as a number of other marine mammal species. In years when upwelling does not occur, or is disrupted by anomalies in global weather patterns, such as in 2005 and 2006, these species may be absent or much rarer.
We in the Bay Area are lucky to be able to witness these endangered leviathans firsthand. Driven nearly to extinction by whaling in the 20th century, the blue whale’s numbers are still far below pre-whaling population estimates. It is thought that there are around 4,000 blue whales in the northern hemisphere, a far cry from their world-wide pre-whaling population of over 300,000.