I don't know how many in total, but with the latest one being one of the biggest ever to date it's almost irrelevant. The damage once this hits the shore is going to be huge.
My Idea in how to stop the leak is the following, insert an very strong Balloon into the pipe, it has to be deflated and have a heavy anchor on the bottom, when the ballon is in the pipe inflate the balloon and while it gets bigger and bigger the pipe will get smaller and smaller until it is totaly closed. I use a smaller system when my drainpipes are clogged up. I think it would work.