Nurse sharks can bite. They generally have a good disposition and a "you leave me alone, and I'll leave you alone" attitude. I once bumped my mask against one's nose when I was looking under a rock for lobster. The shark didn't move, but I sure did.

A friend of mine tried to catch a small nurse shark by the tail and it arched around and clamped on his shoulder. He had to get out of the water to detach it.

Respect,
Col.Andy