Sea Life Safari

Cap'n Lobster is found on the 2nd level, Ship Graveyard. He is located between two rocks just before the entrance to the sunken shipwreck. You need to throw an object at him so he pokes his head out and then take a picture to get the achievement. See the video below.

One important thing to note is that all special items do not show up until after you play a level 2 or 3 times. Just play each level a few times focusing on taking pictures of sealife before you worry about looking for special items.

In the second level just before you enter the ship look left and there he is between two rocks