Non Technical Summary

The numbers of animals recruiting to a population provides information not only about the size of the population but also information that can be used to predict the catch that may be taken in future years. The eastern rock lobster is by far the most abundant species of rock lobster in commercial and recreational catches in NSW. Because all larval eastern rock lobsters entering the population each year cannot be counted directly, their numbers are measured as a relative index. The index is the number of larvae caught on devices known as collectors. It is important when measuring the relative abundance of individuals in this way that sampling is done in a consistent manner. His means that it is necessary to have a knowledge about the behaviour of the larvae with respect to the sampling device (collector) and how environmental factors may affect this behaviour. The behaviour of many species is known to be influenced by the lunar cycle, and the numbers of larvae caught on collectors may also depend upon the length of time since the collectors were last sampled.

This paper describes an experiment to determine whether the lunar cycle affected catches of larval eastern rock lobsters and, if so, at what time of each lunar month sampling should be done. It also investigated how long collectors should be left between sampling times to catch the most larvae. Results showed that more larval eastern rock lobsters were caught on collectors during the new moon and first quarter than at other times during the lunar cycle and that more larvae were caught on collectors that had been sampled at four weekly intervals.

Knowledge gained from this study was incorporated into a standard sampling strategy to collect information on the distribution and abundance of larval eastern rock lobsters. This study provided the evidence that it was best to sample collectors for eastern rock lobster larvae every four weeks around the first quarter of the lunar cycle. Data collected will provide information about (I) whether management measures to protect spawning stock of eastern rock lobsters are successful in increasing recruitment to the population, (ii) the main nursery areas for eastern rock lobsters along the coast of NSW and (iii) the relationship between recruitment and the level of catch that can be expected from the fishery in future years.