Our first time out in the water was to snorkel for abalone, a shellfish.  Abalone cling tightly to rocks and you need a knife to pry them off.  This is challenging considering you have to dive down in a dry suit, while holding your breath, and holding onto a collection bag.  The trouble was all worth it.  We caught our limit, cleaned them, and stuffed ourselves that night with their wonderful taste.  It is difficult to hand-clean abalone so we threw them into the washing-machine and gave them a 15 minute go-around.  That seemed to do the trick.