First part was coming up with an idea, I sketched this guy, but I scrapped him since I didn't like him. I thought he should have an honorable mention though.
step 2 of 3
Here I have the basics laid out. Some of it's sketchy but after he was fleshed out I went back in and cleaned up the lines.
step 3 of 3
I added in the shadows and texture- mainly by using my eraser for scale highlights. I added in some additional things- shadowed seaweed, bubbles, feathered in the fins a bit. I then Scanned in the final picture. The other steps were with digital camera.