John Varley's Eight Worlds series has an alien species called the Invaders. They invaded Earth to protect cetaceans from the effects of human civilization. The

John Varley's Eight Worlds series has an alien species called the Invaders. They invaded Earth to protect cetaceans from the effects of human civilization. The Invaders divide sentient life into three tiers - species like themselves that evolve in gas giants, cetaceans, and vermin; we're in the third category. [0] https://en.wikipedia.org/wiki/Eight_Worlds https://en.wikipedia.org/wiki/Eight_Worlds