Depends where at. Never any issues with sharks here in Bali. Certain spots in Australia & elsewhere, common.
Though even without them, surf always carries certain risks if the waves are decent sized. I had a bail in February, surfboard smacked me on the head HARD and triggered a chain reaction of craziness. Haven't been out lately, still shooken up from the whole thing and body not fully healed yet. I can't imagine how much a shark encounter would shake a person up...
check this out @rok-sivante http://ktla.com/2016/05/05/face-to-face-with-sharks-with-photographer-michael-muller-and-his-new-book-exhibit/#ooid=w3NWtiMzE6gpO-Xv8LG4uOCChHPZXbtz