I'm talking about the time spent between book 23: the pretender and book 48: the Return. Yea, we all know he was on that island, but what did he really do all that time? We're talking about a year and a half, really. He couldn't have just shouted out to the sea through thought speak like he did to that kid in the solution. Think about it; how far away could this island possibly have been from shore? A year and a half is more than enough time for someone to have passed by.
Did he give up hope of being saved? Did he really shout all the Animorphs secrets out to the sea?--the whole question of how far away the thought speech range is. Did he have a routine: hide, eat, hide, scavenge...hide?
I don't know...What do you think he did before Crayak saved him?
Also, what do you think the deal was anyways? I doubt David would have bothered if he thought Crayak wouldn't have restored him to his human body.