On Saturday, July 27, the film Sharkwater screens at 8 p.m. at the Katherine Cornell Theatre in Vineyard Haven. The documentary directed by Rob Stewart, aims to debunk stereotypes of sharks as vicious killers of the sea. Mr. Stewart’s film travels the oceans of the world exploring the lives of sharks, the people seeking to protect them and others who try to exploit and kill them, including shark poachers in Guatemala and marine reserves in Costa Rica and the Galapagos Islands.