Along with what Alex pointed out, in just about any kind of picture UW or land the brightest spot in the picture is where your eye will go first. I like all the pics, your composition is just great on all of them.
The last one with the shrimp you usually don't want to center the subject right in the middle you can crop in many different ways, I cropped out the strobe light comming from the right side where it was the brightest. You can play with it.
Of course it is best to nail a pic right off, but photoshop to the rescue, I used the burn tool a little with a teeny tiny bit of shapening and croped the shrimp some, see if you like them. A minimal enhancement to some great shots.

