Kick them in the nuts.
Or try talking to them , soothethe shark out of agression.
Dont take my advise honest its not the best sometimes.
Actually I have surfed with sharks & they have not seemed interested at all.
the more noise you make the better , I hear that we dont generally make noise like fish do , but then again in Aus we get the odd attack , maybe its cause surfers look like seals from below or they were making seal sounds or..they peed in their suit ....is this one true I have heard it for years ....done t for years and still have all my limbs ( including diving ) .
I think if its gonna happen their is not much you can do about it , I personally will try to gouge it and punch it , unless it has taken my arm or head off with one bite .. then I might just go with it & bleed out.
hmm I think running away as soon as you see it is good too....get air & try to lose it in the air some how.....more jumps less chance of it getting you , sharks are fast swimmers too right !!!!
Then again more jumps = more chance to come off and crash....
I always carry my diving knife in case of lines wrapping me ....sharks dont like knifes much either.
Think lots of ...I dont taste like Tuna ( or Chicken ) thoughts.......