Why Studying Sevengill Sharks in San Francisco Bay Matters
When you think of San Francisco Bay, you might picture the Golden Gate Bridge, Alcatraz Island, or the city’s iconic skyline. But how many of us think sharks? I sure do—and that’s where our work began.
One of the largest apex predators along the northeastern Pacific coastline, the broadnose sevengill shark, is a regular visitor to San Francisco Bay. These sharks can grow up to 10 feet (3 meters) long and weigh around 350 pounds (160 kg), making them an impressive species to study. Sevengill pups have been documented in the Bay as far back as the 1940s, but does the presence of juveniles automatically make this a nursery area? Not necessarily.
A colleague, Kimberly Stauffer, fishing for sevengill sharks by the Golden Gate Bridge in San Francisco, CA. Photo © Meghan Holst
In 2007, researcher Dr. Michelle Heupel and colleagues established three key criteria that define a nursery habitat for sharks:
- Juveniles must be found in the area more frequently than in other locations.
- They must remain in the habitat for extended periods.
- The area must be used consistently across multiple years.
A neonate broadnose sevengill shark being ventilated while biologists collect samples. Photo © Meghan Holst
For our project, we set out to confirm whether San Francisco Bay meets all three criteria, officially defining it as a sevengill nursery. But beyond just identifying the Bay’s role, we also wanted to investigate a critical conservation question: How do fisheries interactions impact juvenile sevengill sharks in their potential nursery habitat?
Catch-and-release fishing is often viewed as a sustainable practice, but the reality is more complex. Handling, stress, and exposure to air during capture can have physiological effects that may impact their survival. That’s why, with support from the Save Our Seas Foundation, we’re using an i-STAT Alinity device, a portable blood analyser, to assess stress levels in juvenile sevengills. This allows us to measure key physiological markers like pH and blood gasses immediately after capture, giving us insights into how these sharks respond to fishing interactions.
Meghan Holst and colleagues, Manny Ezcurra and Kim Luke, help bring aboard a juvenile broadnose sevengill shark for sampling. Photo © Gregory Urquiaga
By combining physiological data with long-term monitoring, our work will help us determine not only whether San Francisco Bay serves as a critical nursery ground but also what risks juvenile sevengills face from human activities. Understanding these interactions is the first step in developing conservation strategies that protect these young sharks—and the health of the entire ecosystem they help regulate.