Q: Why are there humpback whales in San Francisco Bay right now? What attracted them here, and what are they finding to eat? — Beth Slatkin, Bay Nature marketing director

Yes, it’s been great to have whales in the Bay! Not just one or two, but up to a dozen humpback whales can be seen spouting simultaneously. Last summer was the first time we experienced a major influx of humpbacks. From sightings made so far, this year is on track to equal the 2016 count. That’s amazing when you consider that, in the past, humpback whales only ventured into the Bay accidentally. Humphrey was the most famous of these lost whales. In 1985, he swam 70 miles up the Sacramento River before he turned around. And in 2007, Delta and Dawn, a humpback mother and calf, were disoriented and spent a month in the estuary before they made it back to the sea.

Today’s humpbacks, however, are definitely not disoriented whales. They’re here intentionally to feast on fish, especially schooling anchovy, which enter the Bay by the millions. Humpbacks feed on fish, or the tiny crustaceans we call krill. When the krill begin to “bloom” in vast numbers offshore in the Gulf of the Farallones, usually by August, the humpbacks will turn their attention there. But until then, the humpbacks are taking advantage of the Bay’s bounty. You can sometimes see them lunging to the surface, their huge throats distended as they engulf a shoal of anchovies.

Cetacean researcher Bill Keener. (Photo by Flip Nicklin)

While the whales have been around since April, they are not permanent residents. Rather, they commute to and from the outer coast in a rhythm that’s timed to the tides. Typically, they enter the Bay on the incoming flood tide and leave on the ebb. The best spot we’ve found to count the whales is atop the Marin Headlands, or from Lands End in San Francisco. You can get closer if you book a tour on a local whale watch boat. But if you want to get a special view, without having to worry about seasickness, then go to the Golden Gate Bridge during a strong rising tide. From the pedestrian walkway or the platform around the South Tower humpbacks can be seen — and even heard — blowing as they forage for anchovy, often accompanied by squealing gulls vying for leftovers.

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The same whales don’t seem to visit the Bay every single day. We know this because we can track individual humpback whales by comparing photos of the flukes, their massive tails. The undersides of their flukes, which they lift high into the air, have natural black-and-white patterns we can recognize like fingerprints. By matching fluke photo-ID images, we learned that at least a few whales identified in 2016 returned in 2017. That’s not surprising, given they are adept at navigating the marine environment and highly motivated to eat. The adults lose weight as they fast on their winter breeding grounds off southern Mexico and Central America, so in spring they head to California where they can bulk up.

Why did it take so long for the humpbacks to target San Francisco Bay? It could be that they didn’t need to explore this area until their population grew and they began to seek out new sources of food. When I started studying whales in the mid-1970s, there were about 2,000 humpback whales in the North Pacific. Now there are more than 20,000. That’s what happens when you stop hunting them.

Threats to our local humpbacks still exist, however. The risk of being struck by a ship increases as the whales transit through the narrow strait into the Bay, along with recreational boaters approaching them too closely. It looks like humans are going to have to make room for these ocean giants. What we thought would be a once-in-a-lifetime experience last year may become repeat performances if the humpbacks continue to spend summers beneath the Golden Gate Bridge. Lucky us. There’s no better place in the world to look straight down into the blowholes of a great whale!

Ask the Naturalist is a reader-funded bimonthly column with the California Center for Natural History that answers your questions about the natural world of the San Francisco Bay Area. Have a question for the naturalist? Fill out our question form or email us at atn at baynature.org!