Southern rock lobster has the longest pelagic larval stage of any rock lobster species. After spawning, lobster eggs/larvae spend one to two years in the open ocean. Surviving larvae then metamorphose into Puerulus at which stage they can actively swim and can settle if they come within close range of suitable shallow habitat.
The long larvae duration and natural variability of ocean currents result in high variability in the number of larvae settling in a given location each year.
Puerulus collectors have been deployed since 1990 at several locations in Tasmania. Four of these locations are now monitored on a monthly basis. These collectors mimic attractive settlement habitat for puerulus and are regularly visited by IMAS field teams to count the number of puerulus, thereby providing a relative index of the number of puerulus settling through time.
In Tasmania the link between puerulus settlement and subsequent growth to juvenile lobsters is weak due to a range of factors that affect survival rates and are not well understood. However, periods of unusually low settlement (e.g. early-mid 2000) have been linked to reduced recruitment to larger size classes in subsequent years and provide an early warning sign for the southern rock lobster fishery.
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