It is a tiny island of rocks, California sea lions and a huge great white shark population due to the sea lions.
A fine place to incarcerate someone really notorious with condition they can swim to San Francisco on their own.
Felon is blubberous enough to be taste to a great white.
It's why Alcatraz was so notorious. Back in the day, the great white population in San Francisco Bay was considerable too.

During WWII there was a contest about what to do with Hitler if he was captured. One winner was a little Black girl who proposed his skin be dyed black and he be let go anywhere in the deep south.