how to make a crab farm (oceanCraft mod for 1.7.10)

1.dig a hole be sure the floor is sand and must be more than 2 blocks wide unless it won't work

2.find some shells must be the kind that's in the pic

3.collect the shells and put it in the hole

4.wait a few seconds and break the shells

5.and baby crabs might come out of the shell

WHY? BECAUSE WHY NOT?