Sunday, February 8, 2009
Seven gill sharks are called that because unlike most modern day sharks, which have five gill slits on either side of their head, seven gills have seven. There are only a few other sharks which have more than five gill slits, namely the six gill shark, and the sharp-nose seven gill shark. These sharks are considered some of the most primitive sharks alive today. The seven gill generally hangs out under the golden gate bridge area, as it is the deepest part of San Francisco bay. They are also the largest shark in the bay, reaching 10 ft (~ 3 m) in length. The largest shark in the area, the white shark, does not enter the bay as it cannot tolerate the brackish water.
Back in the day, these guys were heavily fished for their oily liver. The fishery in San Francisco collapsed in the 1940s due to heavy fishing. They seem to be making a bit of a comeback, although there is no official data on their status. They are doing a tagging and tracking study on these guys, to see exactly how they use the bay, so maybe we can also get a better idea of population numbers too.