VELVET SWIMMING CRAB Rockpooling is fun at any time of the year, but is best on spring tides, which occur twice monthly. On such tides, the sea retreats farthest, exposing the largest extent of rock. Take advantage to explore sheltered shores for stunning marine creatures such as Velvet Swimming Crab. Flattened rear legs help it swim and burrow, and the carapace is soft (velvet) to the touch. Take care, though: it's not shy of giving a sharp nip.