Sharks of San Francisco Bay

Oct 31, 2019

Great White sharks swim along the Pacific Coast September through December. That’s why Bay Area surfers often call this season "Sharktober"— an especially fitting time around Halloween for retelling scary tales of close encounters. These sharks starred in the classic thriller Jaws because they’ve been known to attack surfers and swimmers, and chomp surfboards and kayaks.

Don’t worry, though. Great Whites rarely enter San Francisco Bay. The most recent sighting was last July, when a boat captain accidentally hooked one in the Bay (and then released it, as required by law). Eleven other types of sharks live in Bay waters, but they don't typically prey on people. And since these sharks mostly hang out along the muddy bottom of the Bay, few people—including Bay swimmers—ever see one. 

The Bay's most common shark, the leopard shark, lives here year-round. Named for the beautiful pattern of dark brown spots on a steel-grey body, it can grow up to six feet long. Leopard sharks use their snouts to dig in the sediment and eat shrimp, worms, clams, and fish eggs from the Bay floor. 

Because leopard sharks can live for decades, consuming creatures from the contaminated sediment at the bottom of the Bay, their bodies also accumulate a lot of toxins, like pesticides, mercury, and heavy metals. That poses a risk for people who eat leopard sharks from the Bay. 

State health authorities advise that women under 45 and children under 17 should never eat any type of shark caught in the Bay. For others, a maximum of one serving of shark meat about the size of the person's hand per week is considered safe. 

Despite this warning, people regularly fish for leopard sharks in the Bay and share shark recipes online. They say the meat tastes like salmon.

Leopard sharks do have predators in San Francisco Bay, including sea lions and the Bay's largest species, sevengill sharks. Sevengills are named for the seven sets of gills on each side of their body. They are black and gray, grow as long as 10 feet, and can weigh over 300 pounds. 

In addition to eating smaller sharks, sevengills also eat harbor seals. These sharks are in the Bay during spring and fall, and they may migrate into the Pacific during winter. 

Two other smaller Bay sharks are the reddish-brown smoothhound shark, and the Spiny dogfish, which has a needle-sharp spine sticking out from one of its fins.

Worldwide, the greatest threat to sharks is finning, the practice of killing sharks to eat their fins. The fins are used to make a luxury food prized in China and other parts of Asia, shark fin soup. The US and some other countries have banned shark finning. But according to our nonprofit partners at Shark Stewards, globally 100 million sharks are still killed for their fins every year.  

In San Francisco Bay, aside from toxic pollution, a big threat to sharks is a parasite, Miamiensis avidus. In late spring of 2011, 2017, and 2019, this parasite killed large numbers of Bay leopard sharks.  

The die-offs happened after rainier-than-usual winters, when leopard sharks migrated to the Bay's shallow waters to mate and give birth. Scientists believe that the sudden deaths were caused by an infection related to the parasite. The heavy rains may have made the sharks more vulnerable to infections due to lower levels of salt in shoreline waters and higher levels of pollutants washed into the Bay by the storms. 

Baykeeper fights the toxic pollution that makes sharks caught in the Bay unsafe for people to eat and that may contribute to springtime shark deaths. We also work to protect the Bay's sediment and sharks from harmful dredging practices. And we're standing up to stop unwise shoreline development that destroys wetland habitats where young sharks are born and grow. 

If you ever spot a San Francisco Bay shark, consider yourself lucky. You're unlikely to be its next meal, but you’ll have a great Sharktober tale to tell! 

Photo of a leopard shark above by J. Maughn, Flickr/CC

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