What is the fine-grained topic of the following text: "Blackfish" is the story of Tilikum, a captive killer whale that has taken the lives of several people, and which underscores problems within the sea-park industry, man's relationship to nature, and how little has been learned about these highly intelligent mammals. Only return the topic.
The documentary "Blackfish" focusing on Tilikum, a captive killer whale in the sea-park industry.