The game only allows two grendals on the ship at a time. To have no more grendals, but be able to get them back, shoot all grendals on ship with mud-blaster, then when the new eggs appear (HINT: they always appear right beside the pirhanna pit in the grendal world) toss them into the pirhanna pit. Notice how the pirhannas don't eat them! The mother greandal now thinks she has two grendals walking on the ship, when actually their eggs are sitting there, never to hatch. If you want the grendals back, just take the eggs out!