Here's my two cents:
1 - The color of the shark is beautiful and rich! Love the underwater caustics.
2 - This one is super nit-picky, but his leg and foot do bother me a little. Not because the foot is to big, but I think the pose is difficult for me to grasp. I am having a hard time visualizing how he is sitting on the board. He's not straddling it, since we can only see one leg. The weight seems off, like he's slipping off or something thing.
3 - I don't particularly like the compositional choice to have the clouds be directly behind the characters. The splashing blends too much with the clouds, which is making the image less clear. That is to say, it's hard to distinguish what is forground splashing and what is background clouds. It could work to add some atmospheric perspective to the clouds, or simply remove them so you have crisp contrast against the blue sky.