Research has indicated that puerulus will settle onto collectors (which mimic floating seaweed).

Most settlement occurs during the period of no moon and ceases when moonlight intensity rises above 10% of full moonlight.  Sampling during the full moon period ensures that the samples are representative of the previous month’s (dark-moon) settlement period.  Each panel from each collector is shaken a prescribed number of times and any puerulus present are counted. 

The puerulus migrate from the coastline westwards and then move northwards against the direction of the Leeuwin current which runs along the coast from north to south.  Since puerulus numbers generally peak in Spring and are their lowest in Autumn, the settlement season is considered to start in May and end in the following April.  At the end of the settlement season, in April each year, a seasonal average is determined, which is the sum of the monthly averages from May to April, inclusive. This seasonal average has consistently shown a strong correlation with the abundance of lobsters three to four years later.

Environmental factors, such as the strength of the Leeuwin Current, winter/spring westerly wind patterns, and water temperatures, play an important role in the survival and settlement of puerulus and thus the numbers that are counted.

This year the prolonged spell of high daily temperatures had led to the water at the Ningaloo Reef habitat, for example, to be 5 degrees higher than usual and this is likely to have a devastating effect on the numbers of abalone and scallops along the coast, and may negatively impact the numbers of lobsters available to catch in 2029-30.  We’ll know more in May.  Any good news? At the moment, likely numbers of octopus and crab seem to have been unaffected by the higher water temperatures.