Science Fiction Beowulf Book?

I read this book about ten years ago, so it's at least that old. It was a science fiction book about a group of colonists that go to another planet in space and encounter some odd alien creatures. There is very limited life on the planet, and they eventually discover that the life forms are all related, e.g., the fish they find actually turn into the monster that gets compared to Grendal. Anyway, there is a lot of blatant Beowulf symbolism, but I can't remember the name of the book.