Overview
In October/November each year, prepubescent western rock lobsters, around 60-90 mm in carapace length, undergo a synchronised moult. This moult results in a colour change from their usual red, to a paler pink shell, and it is this pale pink shell that has led to them being colloquially known as “whites”.
In late November / early December many of these whites will undergo a mass migration, moving in large numbers from their inshore reef habitats, which are dominated by juvenile lobsters, to the deeper offshore reefs, where the majority of adult lobsters reside. During this migration, the whites move long distances across largely sand dominated habitats. Their migration occurs in two main phases; an offshore phase from shallow to deeper waters, and then an along-shore northern migration in the deeper waters (100 – 200 m). At the completion of this northward deep-water migration, which occurs to the westward side of continental shelf reefs, lobsters appear to move eastward and settle on deeper-water reef systems; between 30-70 m water depth. Upon reaching these deepwater reef habitats, white lobsters will progressively return back to their regular deep-red colour shell. Some lobsters will undergo an additional “white phase” in the following year, being capable of at least two migrations in a lifetime. It appears that the attainment of sexual maturity marks the end of any migratory movements, with visual assessments indicating that all female whites are immature (George 1958). While it is assumed that male whites are also immature, sexual maturity is more difficult to discern in males and so no data is available to confirm this. However, a comparison of male size at sexual maturity and the size of migrating lobsters indicates that male whites are below the size at sexual maturity and therefore likely immature.