Creature Feature: Sevengill shark

7 gill

In keeping with our shark theme for the year, we are going to talk about another shark that we see in the San Francisco Bay Estuary: the Sevengill Shark, Notorynchus cepedianus.

Three guesses as to how this shark got its name! (You probably won’t need the last two)  Indeed, they have 7 gill slits on each side of their heads! Most chondrichthyes (that means fish with a skeleton made of cartilage) have only five gill slits per side. Sevengills have a beautiful silver grey colorization with speckles on the top half of their body. This species of shark can reach about 10 feet long.

Sevengills are open water sharks that will travel in and out of the bay. It is thought that they travel into the Bay for two main reasons, the first being to breed. Just like our local leopard sharks they, are ovoviviparous, meaning giving live birth. The estuary is an especially safe environment for young animals to get used to fending for themselves. The second reason sevengills are thought to venture into the Bay is to feed. They will eat just about anything that they can physically get into their mouth, including leopard sharks!

As we know, the teeth of sharks vary in shapes and sizes. One way to understand how shark teeth work is to think of them like a knife and a fork. Sevengill teeth compare particularly well with this analogy. Sharks sink their comb-shape bottom teeth into their prey (spearing it like a fork) and move their heads to that their upper teeth saw into the flesh like a knife, cutting their prey into easy to swallow chunks. Gross but fascinating

Sevengill sharks were, at one time, a highly exploited fishery.  In the 1930’s, Sevengills in the San Francisco Bay were overfished for the oils that can be rendered from their bodies. Today, they are still fished for human consumption, oils, and shark leather derived from their skin.  The World Conservation Union (IUCN) has the Sevengill listed as “Data Deficient,” meaning that there is not enough data collected from the regions in which they are found. In the Eastern Pacific, Sevengills are considered “Near Threatened.”

References:
Edited by KC O’Shea
Photography: MSI Gallery
http://aquariumofthebay.org/pages/detail/1596
http://www.montereybayaquarium.org/animal-guide/fishes/broadnose-sevengill-shark
http://www.flmnh.ufl.edu/fish/gallery/descript/sevengill/sevengill.html

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