Long-term Monitoring of SF Bay’s Apex Predator: The Broadnose Sevengill Shark

 In EcoCurrent

The Broadnose Sevengill Shark, Notorynchus cepedianus, is an apex predator that migrates along the Eastern Pacific coastline and is prevalent within temperate bays and estuaries. While the species is found around the world, it is unlikely that populations mix between coastlines.

San Francisco Bay and Humboldt Bay are the only documented pupping and nursery grounds for the Eastern Pacific population of Sevengill Sharks, where mature adults aggregate during summer. The only documented breeding ground for this population is in Willapa Bay, Washington. There is severe data deficiency regarding Sevengill Sharks and it’s unknown how their responses to fishing and climate change will influence the rest of the ecosystem.

To address these gaps in knowledge, Aquarium Biologist Meghan Holst and the Animal Care Department are leading a long-term monitoring project of Sevengill Sharks in San Francisco Bay. To answer critical life history questions, Holst and the Animal Care team collect muscle biopsies to analyze diet preferences of all size classes using stable isotope analysis. They also acquire skin samples for genetic analysis to understand the population structure and genetic fitness. To re-identify individuals in the future, researchers apply conventional identification tags and take a profile picture of the spot pattern of the animal. By re-identifying individuals upon recapture, Holst can document the changes in diets and growth of individuals. Additionally, the profile pictures of each tagged individual are uploaded to Ocean Sanctuaries spot-pattern recognition software online, which also allows citizen scientists to upload photos of Sevengill Sharks they encounter in the wild. With this software, researchers and citizen scientists can identify individual Sevengill Sharks as they migrate to other locations.

Holst is leading a collaboration to effectively assess the population with Oregon Coast Aquarium, who is replicating these procedures in Willapa Bay, Washington, and Seattle Aquarium, who is performing the genetic analysis. The next phase of this research will implement acoustic tags that will reveal more information about movement patterns of each size class.

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