Fin whales feeding in summer waters

The fog lifts from the Golden Gate just enough to reveal the dark line where San Francisco Bay meets the Pacific. Out there, beyond the shipping lanes and beneath the surface chop, fin whales are feeding. These waters hold them through the long days of summer, when krill and small schooling fish gather in dense clouds along the continental shelf.

A fin whale surfaces with barely a splash. Eighty feet long, it moves through the water column like a living current. The whale's throat pleats expand as it lunges forward, mouth open, engulfing thousands of gallons of seawater thick with prey. Then the pleats contract, forcing water through the baleen plates while tiny fish and crustaceans remain trapped inside. This is rorqual feeding, a technique that turns the whale's entire body into a filtering machine. The fin whale can take in more water relative to its body size than any other baleen whale, processing tons of prey-rich seawater in a single gulp.

These summer waters off the Bay area support some of the most productive feeding grounds on the Pacific coast. Upwelling brings cold, nutrient-rich water from the deep ocean to the surface, fueling blooms of phytoplankton that feed the zooplankton that feed the fish that feed the whales. Fin whales follow this abundance, timing their presence here with the peak of the upwelling season. They feed primarily on northern anchovy, Pacific sardine, and euphausid shrimp. A single adult fin whale can consume up to four tons of prey each day during intensive feeding periods. The whales often feed cooperatively, working together to concentrate schools of fish or krill before lunging through them in coordinated attacks. Brown pelicans and Heermann's gulls gather above these feeding events, diving for the scattered fish that escape the whales' massive mouths. Brandt's cormorants join the feeding frenzy from below, pursuing fish driven toward the surface by the whales' movements. This creates a temporary community around each feeding event, linking the largest animals in these waters with some of the smallest seabirds.

Listen for the sound of their breathing. A fin whale's blow carries across calm water as a sharp exhalation followed by a deep inhalation, audible from more than a mile away. Between breaths, they disappear for five to fifteen minutes, diving to depths where the summer light fades to blue-black and the pressure would crush any air-filled lung. Down there, they hunt by sound and feel, their lower jaws sensitive to the vibrations of schooling fish. When you hear that distant whoosh of breath, you are listening to an animal that has just returned from a world we can barely imagine, carrying the deep ocean back to the surface in its blood and lungs.