Western Rock Lobster have five pairs of legs that are used to move across the ocean floor, the fifth set possessing claws in the female, and six smaller pairs are located at the mouth. The eyes are located at the ends of stalks. Western Rock Lobster vary in colour from a brownish purple to a pale pink colour. The exoskeleton is segmented, and must be shed as the animal grows. The average accepted form of measurement, that of the carapace, is from 80 to 100 millimetres (3.1 to 3.9 in) in length. Western Rock Lobster (Panulirus Cygnus) are caught up to 60km off the coast between Augusta and Shark Bay.
The range of the species is along the coast of Western Australia, from Hamelin Bay to the North West Cape, and at islands such as the Houtman Abrolhos. The larvae of the species develop in the meadows of seagrasses of Western Australia, migrating out from these toward the deeper ocean and coral reefs in areas such as the Abrolhos Islands.
Western Rock Lobster generally spawn and hatch their eggs in deep waters in excess of 40 metres in depth. After spending between 9 and 11 months in the open ocean between 400 and 1,500 km offshore, the tiny larvae (phyllosoma) are carried back toward the coast by seasonal currents.
On their return to the continental shelf they metamorphose to the next stage (called puerulus - smooth, transparent miniature Western Rock Lobster), and swim across the shelf, aided by wind and waves, to settle mainly on inshore reefs where they moult within a week or two into juveniles.
Each year between November and January large numbers of pale-coloured, recently- moulted juveniles (known as whites') migrate from inshore reefs to the deeper reefs offshore. Once at deepwater breeding grounds, the Western Rock Lobster mature and spawn a year or two later, when six or seven years old.
Adult and non-migrating Western Rock Lobster are known as reds' and form the catch between February and 30 June and October 30th.
Environmental factors such as the strength of the Leeuwin Current and its eddies, rainfall, storms, wind patterns and ocean temperatures all affect the breeding success and abundance of Western Rock Lobster from year to year.
Fisheries biologists refer to two stages of what is known as recruitment'; first the annual settlement of the puerulus on the inshore reefs, then each season's entry of Western Rock Lobster which have attained legal size into the fishable stock. The relationship between these recruitment' levels provides a good guide to future catches from the fishery. Efficient catch prediction models based on the numbers of puerulus settling inshore aid the adjustment of management controls to maintain catch and breeding stock levels.