I read this book two years ago at a local library and can't remember the name of it. The book is really old, written in the 60s. It has a peach cover with multicolored text.
It's about a man living in a society on an alien planet where a prison ship had crashed and the survivors banded together to form a society. He gets a promotion to a telegraph operator. I think they called it semaphore operator.
There are giant squid predators that are in a relationship with the human population. They let them live in exchange for food and are worshipped by a theocracy. There is one particular big squid who is the King and he wrecks everything the protagonist had including killing his mentor after the protagonist started talking about how they were not beholden to the monsters.