Often unfairly and inaccurately cast in movies as the violent villain of the deep, sharks play a starring role in maintaining the health of their ecosystem. So much so that their absence would drastically throw their habitat and food web entirely out of whack.
As an apex predator, their top down regulation of prey species indirectly benefits the habitat quality and availability. For example, sharks eat sea turtles, sea turtles eat seagrass, and numerous animals use seagrass as habitat. If sharks are not around to regulate the sea turtle population, then seagrass beds become overgrazed, effectively demolishing habitat and nursery areas for several species of fish and invertebrates.
In other words, when sharks are present, they increase biodiversity in habitats as they prevent any one prey item from becoming too abundant. They also usually hunt fish that are slower and weaker, leaving the stronger, healthier fish to reproduce. This process can prevent the spread of devastating disease outbreaks and strengthen the prey species’ gene pool.
All in all, the loss of keystone species and release of predator regulation over prey populations results in a ripple effect through the food chain, upsetting the balance of a marine environment. Humans have already caused a major decline in shark numbers, and this same thing can happen here in San Francisco Bay.
What effect might the recent die off of hundreds of leopard sharks have on the Bay? What would happen to the sea lion population if there were no more white sharks patrolling the waters under the Golden Gate Bridge? One can speculate at the thought of these impacts on our Bay, or we can affect change through action.
Here are a few things you can do to help our local shark species thrive in San Francisco Bay:
Volunteer to restore Bay wetlands: Often referred to as the “lungs of the Bay” our local wetlands help improve the Bay’s water quality, naturally protect communities from sea level rise, and provides nursery habitat for sharks and other wildlife that call the Bay Area home. Register for a Bay restoration event near you today!
Reduce pollution at the source: Our Bay’s keystone species (among others) need a trash-free Bay to thrive. That’s why we’re now pressuring Bay Area cities to eliminate the flow of trash from city streets into the Bay by 2022, but it will take all of us to accomplish this ambitious goal. Take time to organize or volunteer for neighborhood cleanups, urge your local officials to prioritize stormwater projects, and if you haven’t already take the Zero Trash Pledge!
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 thebroadnose 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!
Check out this week’s Weekly Roundup for breaking news affecting San Francisco Bay.
Curbed 8/7/2013 100 Bird Species Spotted: Heron’s Head Park in India Basin Located along San Francisco Bay south of the Dogpatch neighborhood lies a peninsular park known as Heron’s Head, so named for its shape when seen from above. Developed accidentally by an unfinished shipping terminal in the 1970’s, the park that we now visit was officially opened in 1999. In 2012, the park completed further upgrades and today is visited by thousands for both recreation and education.
The park is mostly made up of a tidal marsh that attracts all manners of bird species (over 100) throughout the year. The removal of invasive plant species will help ensure this park continues to thrive for years to come. Read more>>
SF Gate 8/8/2013 Agency Finds Climate Change Taking its Toll on California California lakes are warming, sea levels are rising, wildfires are spreading, and mountain plants and animals are migrating to higher ground as the impact of climate change takes hold throughout the state, a new report says.
The evidence of the effects of the warming trend emerged in an analysis of 36 “indicators” – warning signs of changes – that are detailed in the 240-page report released Wednesday by the state’s Environmental Protection Agency. Read more>>
KQED Science 8/7/2013 Dolphins Recognize The Calls Of Long-Lost Friends Scientists have known for years that dolphins recognize each other by the sound of each animal’s signature whistle. But it wasn’t known for just how long dolphins could remember these whistle calls.
The individually specific whistle that each dolphin generates before its first birthday “for them functions like a name,” says Jason Bruck, who studies animal behavior at the Institute for Mind and Biology at the University of Chicago.
Bruck says that if a dolphin wants to announce itself to other dolphins, it will let out its signature whistle. And dolphins that are acquainted with each other learn the other’s whistle, just like we learn the names of other people in our lives. Read more>>
SF Gate 8/6/2013 Chevron to pay $2 million for refinery fire A day before the first anniversary of the destructive fire at Chevron’s oil refinery in Richmond, the company pleaded no contest Monday to six criminal charges arising from the incident.
As part of the deal, Chevron agreed to pay $2 million in fines and restitution and accept additional oversight and inspection of its operations during a 3 1/2-year probation period, authorities said. Read more>>
Forbes 8/7/2013 Discovery Jumps The Shark On Shark Week… And Draws Stellar Ratings
Discovery Channel has come under fire from viewers and critics for its program, “Megalodon: The Monster Shark Lives,” which opened opened the network’s “Shark Week”. The ratings were not the problem: Megalodon drew the highest dating for any show in Shark Week’s 26-year history: an estimated 4.8 million viewers tuned in.
But, notwithstanding the stellar performance, the show has triggered an avalanche of complaints about a “minor detail”: there’s no evidence whatsoever that the 50-foot Megalodon still swims the waters. In fact, this monster of the seas died out in the early Pleistocene, 1.5 million years ago. Read more>>
Well, it’s that time of the year…time to pull out your survival kits, shark-esque attire, shark stuffed animals, and underwater creature costumes because Shark Week is officially here. Discovery Channel kicked off shark week on Sunday, dedicating seven days to these wondrous yet incredibly scary marine creatures who roam around the ocean. Even though most of us are weary of coming across sharks in the ocean, “Humans are the #1 predator of sharks, but killer whales, crocodiles, and seals have been known to eat them as well, ” according to the creators of Shark Week at Discovery Channel.
Don’t worry, you do not have to spend all week just sitting on your couch at home as you re-watch shark highlights while teaching your dog to fetch a shark toy. Instead, you can experience your own personal shark viewing out around the Bay! A group of leopard sharks have taken up residence in the former salt ponds from Hayward to Redwood City. Their inhabitance in the Bay is a positive result of better water and biotic qualities of the Bay thanks to wetland restoration work along the shoreline of the salt ponds.
Want to share your love of sharks with your friends and family? Here are some fast facts about those leopard sharks that are swimming around in the Bay:
Each leopard shark has its own unique spot pattern, so there are no two leopard sharks that are alike.
They will never munch on humans as they have tiny teeth. Instead, the leopard sharks snack on worms, small fish, herring, crabs, and other small marine creatures.
Some of their biggest threats include mercury pollution and fishing.
Leopard sharks can grow up to be 6 feet long or even larger.
They can reproduce up to 29 leopard shark pups in one litter.
Their favorite hangout spots are along the surface, and they always swim in a counterclockwise direction.