Make a crossbow out of popsicle sticks (or similar) and elastics and shoot toothpicks at him. If you have shrimp, usually an injury is enough to turn them into a frenzy and they'll eat their clawed brethren alive (you say 'nems are evil.. I say anything with claws is evil .. some are just pretty enough to keep around).
Make sure your aim is good though. I wouldn't trust myself to do this idea at all. "Whoops... Gosh I really liked that clam/fish/insert-something-other-than-undesired-crab here"
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