-( This is a chapter-specific trophy related to: Chapter 3 )-
Once you've made it through the underwater caverns and breach the surface near a tree, dive back down and make it to the depths. If you're close to the walkway where the fox is trying to lead you, all you have to do is dive straight down (taking detours for air bubbles, of course) and you should see what remains of a shark lying at the bottom. Get near enough to it for the trophy to pop.