I know of a guy who was always lugging big doubles around, and he used a HUGE quantity of air. We found out a couple of months later that his left cylinder was a fake - he cut away the bottom, stuffed lobsters in and used the cylinder boot as a cover
He did get caught though... probably had a snitch in his diving club.
We do take lobsters (and other tasty things) on the North Sea - problem is that I reserve every year 10 to 15 trips, and my chosen trips nearly always get cancelled due to bad weather...
Steven