Onset of maturity in male southern rock lobsters Jasus edwardsii in Tasmania,Australia

Summary

The reproductive contribution of male southern rock lobsters Jasus edwardsii has recently become of interest for managing this fishery as changes to the length of seasonal closures have shifted fishing effort towards males. To assess size at onset of maturity, a total of 387 male southern rock lobsters Jasus edwardsii were collected using baited traps from four of the eight fishery regions around the Tasmanian coast during July and August 2000. Sizes at onset of maturity in these samples were estimated by examining the vasa deferentia for evidence of the commencement of spermatid production. In addition, the total combined weight of the vasa deferentia and testis was compared with body size (as a gonad somatic index, GSI). Estimates of size at onset of maturity from the two methods were similar, although estimates from GSI appeared to have broader confidence limits. Although these physiological indices of maturity do not necessarily translate to functional maturity, they indicate that maturity is well below that of the legal minimum size of 110 mm carapace length used for managing the fishery (all estimates by either method for length at 50% sample maturity ≤70 mm carapace length). Production of sperm by males occurs below the size at onset of maturity of females from the same region and spatial patterns in maturity estimated by onset of spermatid production were similar to those of females.