It may have come from your couch, but it is a good question. everything else has significant shadow, even the letters on the building... so interesting question, even if you are on the couch at least your brain is still working. Not to imply there is anything up with the picture but it is interesting... maybe the shark scared it's shadow away.
Probably underneath it. Look at all the other shadows, the sun is high and the shadows are short. The guys behind the fish are obviously quite a few feet behind it and the bottom of the photo only shows about 1 foot in front of the peoples feet. So most likely the shadow is out of frame. There is another photo from a different angle up on Jd's site.