Name of book? Whale-like-creatures telepathically linked to humans, girl is

[Sarah]

main character, big storm? It goes something like this: it was like this chick was on an island with her island people and they think they are the only like civilisation. Anyway when you get to a certain age you get a whale-like mammal as your partner i think, and you can see the ocean thru your "whales" eyes. So they use the whales to find food in the ocean, and once they find it they go out with the whales to get it. So anyways one day she is out and she senses another whale. But this whale doesnt have a partner lad di dah i think she gets caught in a big storm. but thats all i remember. O and i htink she like finds other islands which have like normal people that dont connect with whales or somethin like that