Didn't see it happen often but....

Occasionally when out deep sea fishing someone would hook a shark. They would instantly cut your line if that happened. Never happened to me but saw it happen to people next to me a few times. Couple of times the fisherman had it nearly in the boat before the charter boat guy would spot it.... they would severely scold the fisherman.

It's not sharks that can harm you, either.... ocean is filled with sharp toothed demons.