Leopards, Angels, and Hounds, Oh My! — Sharks in the San Francisco Bay

broadnose sevengill shark
The broadnose sevengill shark is one of six shark species that live in San Francisco Bay.

The Bay Area is lucky to have six resident shark species and one species of ray living in the San Francisco Bay, although there were once more. Several species of sharks are considered threatened or vulnerable because they tend to mature relatively late in life and put a lot of effort into reproducing only a few pups at a time. Most sharks in the Bay rely on wetland areas, which have been reduced by 90% in the past 100 years. The San Francisco estuary was once adequately surrounded by tidal wetlands that provide calm, warm, nutrient-rich feeding, breeding, and nursery grounds for many species of flora and fauna, including sharks. Now, although the wetland areas have become sparse, our Bay sharks rely on these areas for pupping and feeding on smaller fishes (including other sharks) and invertebrate animals that live on the Bay floor, such as clams, shrimp, and crabs. Sharks are important to the web of life because they help to keep other marine and estuarine populations healthy and strong by feeding on weak members, and thereby increasing resources for the strong, which are more successful at perpetuating their population.

The most abundant shark in the San Francisco Bay is the leopard shark (Triakis semifasciata), whose population in the Bay has already greatly benefited from the levee breaches of the former salt ponds in the South Bay. These breaches in the South Bay have re-introduced tidal flow, restoring feeding grounds for leopard sharks, which eat burrowing clams and crustaceans in shallow waters.

We also have angels in the Bay! The Pacific angel shark (Squatina californica) can be difficult to spot in the Bay since they spend a good portion of their time camouflaged on the Bay floor. They are ambush predators, meaning they lie and wait (sometimes for days) on the bottom, slightly buried in the sand. When their preferred meal of flounder, halibut, or crab swims or crawls by, they pop out and snatch it. They have a body form that closely resembles rays and skates but one way to identify an angel shark is to look at its pectoral fins, which are completely attached to the bodies of rays and skates but are distinct appendages in the angel shark.

Our Bay is a popular winter “staycation” destination for the spiny dogfish (Squalus acanthias), which is among the most abundant species of shark in the world due to its global distribution. Although this species is globally abundant, the World Conservation Union has declared that this species is vulnerable to a population collapse due to overfishing. A major reason the National Marine Fisheries Service declared the spiny dogfish fishery is not sustainable is because this shark has a gestation period of up to 2 years, which is the longest known among all sharks! This shark is named for its poisonous spines located in front of each dorsal fin (they’ve got two), which they use for defense against larger prey, such as the broadnose sevengill shark, which also lives in the Bay. Spiny dogfish eat smaller fishes and crustaceans, which are easily found in the Bay, but the spiny dogfish must go offshore to satisfy its appetite for squid.

We’ve got two species of smoothhound sharks in the Bay, which are among the few sharks that give live birth, as opposed to using egg cases. The two species of smoothhounds in the Bay are most easily distinguished by color, brown and grey. Brown smoothhounds (Mustelus henlei) tag-team the spiny dogfish for entrance into the Bay during spring and summer to pup and benefit from this glorious nursery ground before returning to open waters for the rest of the year. The grey smoothhound (Mustelus californicus) is often found hanging out with schools of leopard sharks, which have a similar diet of shrimp, crab, clams, and small fish.

The top predator in the Bay is the broadnose sevengill shark (Notorynchus cepedianus), except when good ol’ Whitey (white shark, Carcharodon carcharias) enters the bay briefly for a sevengill snack. To be clear, white shark tagging studies have shown that white sharks will enter the San Francisco Bay only occasionally and for brief stints, so they’re not considered to be residents of the Bay. The broadnose sevengill preys on small marine mammals and fishes, including sharks and sometimes even smaller sevengills. The sevengill is named for having seven pairs of gill slits, as opposed to the five that most sharks have and is considered to be among the least evolved of all sharks. The broadnose sevengill is a voracious predator but does not dine on humans. Sevengill sharks were once prevalent along the entire California coast and a common catch in the commercial fisheries until the fishery collapsed due to population decline. Sevengill populations now seem to be reduced to two areas, San Francisco and Humboldt Bays, which indicates that conservation of these areas are important to the future of this species.

We also have the bat ray (Myliobatis californica) in the Bay! Bat rays are common in bays and estuaries from the Gulf of California up to Oregon and they are a preferred snack for the leopard shark. Did you know that sharks, rays, and skates all belong to the same class of species called the Chondrichthyes? They all share common features that separate them from other fishes, the most notable being that chondrichthyans all have cartilaginous vertebrae and modified scales, called dermal denticles, which are structurally similar to teeth. These dermal denticles are what give sharks, rays, and skates their dual directional skin texture.

Humans have had a complicated relationship with sharks. Although humans have been the top predator of many shark species, it is the sharks that humans have demonized for quite some time. The word “shark” often evokes images of a larger-than-life “great” white shark with powers to snatch humans off of 36-foot boats. More recently, shark researchers and naturalists have worked hard to counter that evil image by downplaying the sharks’ potential to harm humans. While I believe this downplay has been an important counter for the shark reputation, I think it’s important to maintain a solid respect for sharks in general by respecting their role in the ecosystem as well as their ability to harm humans if provoked. Sharks are absolutely necessary for ecosystem health and the majority of sharks will leave you alone if you do the same. No sharks living in the Bay have ever been documented to kill humans, but most of them can harm you if you bother them. Sharks are highly instinctual – they’ll usually stay away from you if they can. They don’t want to kiss you, and if you get your fingers near their mouths, they can do at least as much damage as a dog.

Humans have almost decimated several species of shark, but sharks have done no such damage to the human population. A great example of human-caused near decimation of a shark species is the soupfin shark (Galeorhinus zyopterus) in the San Francisco Bay. The Bay was once an important nursery ground for soupfin sharks but since the soupfin shark Pacific coast fishery collapsed in the 1940’s due to ruthless and inhumane overfishing for its fins, they are now a rare sight within the Bay. In this light, one might consider humans to be the monsters. This human tendency to exploit nature for its own purpose is the same tendency that enabled the decimation of wetland habitats, leaving us with a mere 10% of what we used to have.

Save The Bay, our partners, and supporters have made great strides in advocating for saving and creating more wetlands.  However, when it comes to reaching our collective goal of establishing 100,000 acres of healthy wetland habitat in the Bay, “we’re gonna need a bigger boat”. We need as many people as we can get on this “boat” to help conserve and restore habitat that will help natural populations thrive. Breaching levees and allowing natural tidal flow to the ex-Cargill salt ponds has re-introduced some of those important shark feeding and breeding grounds that have been lost. Save The Bay works to restore function to the SF Bay wetland ecosystem, including those former salt ponds, by providing native vegetation in the transition zones between those wetlands and the upland habitats. Among other things, this vegetation ensures a healthy detrital input to the wetland, which then fuels the food web that these sharks need.  The sharks are doing their part to help keep populations healthy, and we’re continuing to provide more and more habitat to enable that action. I’d like to thank all of our volunteers and partners who have worked to achieve 45,000 acres of healthy wetland habitat, now we just need 55,000 more!

Help us to support wetland restoration by providing the essential vegetation for a healthy and functional estuarine ecosystem. Sign up to volunteer.