I'm really surprised that's all the damage that was done. If he gets hungry enough, he will get over into the other chamber where the food is.
I would be surprised if you catch him without a baited trap (small crab) unless you take all the rocks out and he/she is in one of them.
Good luck!
I baited the trap with a chunk on shrimp and it wasn't interested. Would a sacraficial crab/snail be better?
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