Relationship Between Indices of Juvenile Abundance and Recruitment in the Western Rock Lobster (Panulirus cygnus) Fishery

Abstract

Indices of abundance of 3- and 4-yr-old juvenile western rock lobsters (Panulirus cygnus) were used to determine the status of the stocks between the puerulus stage and subsequent recruitment to the fishery. These indices were based on logarithmically transformed catch rate data of undersize lobsters obtained from a monitoring program which commenced in 1971–72. The juvenile indices were determined from regression coefficients associated with the factor "year", adjusted for other factors, e.g. location, month, depth, soak time, which affect juvenile catch rates. A revised index of recruitment was based on logarithmically transformed catch rates, in depths up to 18 m. A 7-d moving average was used to smooth out daily fluctuations to enable the "best" 60-d catch rate over the period of recruitment to the fishery (November–January) to be determined so that differences in the time of recruitment may be taken into account in quantifying the level of recruitment. This index is compared with a previous recruitment index based on total catch divided by total effort during November–December. The relationships between the abundance indices of 3- and 4-yr-old male juveniles and the recruitment index resulted in correlations of 0.95 and 0.93, respectively, from the log–log analyses of 11 year-classes with a multiple correlation of 0.97 when the 3- and 4-yr-old indices were used in a multiple regression. These indices provide an independent method to support or modify the prediction of recruitment based on an index of abundance of settling puerulus (aged 9–11 mo) obtained 4 yr before they recruit into the fishery.