I'm looking for the name of a Poul Anderson short story (written prior to 1979). The short story involves a lone space traveler who finds a planet inhabited by a dolphin-like race. He befriends the species, but after doing research on what would happen if more humans come, he begins killing them. One detail I remember is that their blood was green.
I really appreciate the help. Thank you!
That is Sister Planet, See wiki article at https://en.wikipedia.org/wiki/Sister_Planet
Although it is decided not to continue with the terraforming project, and even to destroy the research before it can be reported to Earth, Hawthorne knows what he must do to stop a repeat of the research by others. He sabotages the colony, leaving no-one alive but him, and shoots many cetoids [including one whom he has befriended and nicknamed Oscar] , to make them distrust and fear humans. As he recognizes Oscar's dead body, he thinks to himself "Oh God. Please Exist. Please make a hell for me."
He notices that Oscar's blood is green.
