Spring in the San Francisco Bay is a time to celebrate new beginnings, including the lives of young sevengill sharks. The San Francisco Bay is thought to be the primary pupping ground for sevengills on the West Coast. Every year, sevengill sharks swim out of the depths of the ocean and share an important part of their lifecycle with our local ecosystem. Broadnose sevengill sharks give birth to anywhere from 80-100 live young at one time after carrying them in utero for up to two years—just take a second to think about that! And the wildest part is that all this life and nurturing is happening in our Bay!
The sevengill is a cow shark named for its unique set of seven large gills. Most other sharks only have five. Although sevengills vary in color, they’re often speckled and grow to lengths of 8-10 feet.
These sharks spend most of their adult lives offshore in depths from 300-600 feet below sea level and are distributed worldwide in temperate waters, with the exception of the Northern Atlantic Ocean. In the San Francisco Bay, the sevengill shark is considered an apex predator because it feeds at the top of the food chain. Like many sharks, the sevengill eats small fishes, skates, rays and other sharks; however,
it has a pretty unusual hunting technique. The sevengill shark uses the power of numbers to hunt large, ominous prey. Groups of sharks will circle up around a large target, such as a larger shark or cetacean, and slowly tighten their formation. When the animal is successfully trapped, the sevengills rush in and commence group feeding.
For all of its prowess, surprisingly little is actually known about the sevengill shark and its behaviors—especially offshore. Up until recently, these sharks were not widely studied and from the 1930s-1960s, the seven gill shark was decimated by an aggressive shark fishing and sport fishing industry. We do know that the San Francisco Bay is the primary nursery for young and juvenile sharks, that habitat loss to our Bay could be detrimental to the survival of Western sevengill sharks. But all is not lost. Thanks to Sea Stewards, a local non-profit dedicated to protecting sharks and other marine life through policy, education and advocacy, diligent work to tag and study sevengills in the San Francisco Bay has been conducted in order to uncover information about the movement, behavior and migration patterns of these wonderful sharks. This research will help us learn a little bit more about one of our amazing neighbors. As apex predators at the top of the food chain, sevengills are an important part of the ecosystem. It is up to us to ensure that we do our best provide a healthy bay for them to flourish.
How can you help provide a healthy ecosystem for sevengill sharks? Support our Living Shorelines Program, which is working to improve subtidal habitat in our Bay.
