I read this a while back so don't remember allthe details. I think whatever happened once the ship sank and Pi was stranded in the raft, was a mixture of delusion and hysteria taking over his mind...so its dubious whether whatever he narrated from that point on, really happened.
As for the scientists, he pretty much told them what they wanted to hear, I think... maybe because he knew he wouldn't be believed otherwise (especially by scientific people)...
Hope this hasn't confused you more...?