Bay Crossings Article

Gray Whales—San Francisco Bay’s Frequent Swimmers?

Deb Self
From the May 2012 edition of Bay Crossings

Are gray whales coming into San Francisco Bay more often? Baykeeper is helping to find out, and you can help, too.

We’re assisting the Oceanic Society with a new study to find out how many gray whales are coming to the Bay and what dangers they face. The public is encouraged to help by reporting all whale sightings.

Gray whales can enter San Francisco Bay any time of year, but they’re most likely to swim through the Golden Gate between March and May. Often, the first sign of their presence is their "blow"—a 10-15 foot white cloud of breath they exhale through the top of their heads.

Adult female gray whales are up to 45 feet long and weigh as much as 35 tons, with males slightly smaller. They can live up to 60 years. Newborns are 15 feet long and weigh about a ton. A calf drinks 50 to 80 gallons of its mother’s 53-percent fat milk per day. (Heavy whipping cream, by comparison, is around 40 percent fat.)

When these magnificent whales stop in San Francisco Bay, they are in the midst of one of the animal world’s longest migrations. They swim over 12,000 miles round trip each year between their summer feeding grounds in Alaska’s waters and their winter homes in Mexican lagoons, where they mate and give birth.

However, not all gray whales make the long migration. A group lives year-round off Canada’s Vancouver Island, and a few spend many months off the Farallon Islands.

Gray whales eat little or not at all at their winter homes and during migration. The real eating happens once they get to the waters off Alaska, where for four months, adult whales eat an average of 660 pounds of food each day.

To feed, a whale dives to the bottom, rolls on its side and draws sediments and water into its mouth. As it closes its mouth, water and sediments are expelled through the whale’s baleen plates, which trap food inside. The gray whale diet is mostly small shrimp-like bottom-dwelling animals called amphipods. Some gray whales also eat herring and krill, like their relatives, humpback and blue whales.

When the Golden Gate Bridge opened 75 years ago, gray whales had been hunted to the brink of extinction. Only about 1,000 were left. Now, the population is around 20,000 along the west coast of North America, with 100-200 along the Asian side of the Pacific.

The gray whale was removed from the U.S. Endangered Species List in 1994, but there is controversy over whether the whale has truly recovered. Some scientists believe 20,000 to be close to the numbers before whaling decimated the species, but others say there were as many as 120,000.

If you’re out on Bay and see a gray whale or its blow, watch and feel lucky—but please steer clear. Boats need to stay at least 300 feet—about the length of a football field—away from whales. It’s important for boaters to not cut across a whale’s path or make sudden speed or directional changes.

Don’t let your boat get between a mother whale and her calf. If separated from its mother, a calf may be doomed to starvation.

A study conducted by the Oceanic Society a decade ago found that most whales who entered the Golden Gate ventured only a mile or two into the Bay. But some went as far as the Delta past San Pablo Bay, and a few ventured far into South Bay. They came often—on 98 days during 2001.

Why are whales visiting the Bay? "No one really knows. They may be resting. Some may be exploring, especially juveniles, who are not as focused on getting back to the Alaska feeding grounds as the pregnant females are," said Birgit Winning, Oceanic Society president.

Whales may face dangers here. When feeding from the Bay floor, whales might scoop up mercury and other toxics along with tiny sea animals. They may also suffer collisions with boats, or damage from underwater noise pollution, which is linked to whale strandings and deaths.

Baykeeper is helping collect data for this study from our patrol boat. If you see a whale in the Bay, either from a boat or from the shore, you’re encouraged to take part in this research. Please report the sighting at And if you’d like to learn more about Baykeeper’s work to protect the Bay and its wildlife, visit or contact Deb Self at