bother-in-law kev knows all about catching crabs.  first you attach a fish head (or bacon) to a hook

 then you dangle it off a pier

 then everyone gathers round and waits

 until you pull the line up with a crab attached to the fish head

 when you've got a bucket full (we had 20), display them proudly

 preferably against a moody sky

 and finish off with a nice crab race