He could be enjoying the waves, or....may be fixing to die or is already dead. One thing need to do is keep an eye on him. You can pick him up and see if he goes back in his shell, if he doesnt moe its most likely hes dead. Keep an eye on it for a couple days if it is still moving tonight, and if it pulls into its shell and doesnt move for more than a day or so, pick it up and smell it, carefully...if it stinks, its dead.
Blue