Evaluation of population genetic structure in the western rock lobster

Abstract

One of the assumptions underlying current management of the western rock lobster fishery is that the breeding stock is comprised of a single, genetically homogeneous population. This assumption is based on the extended pelagic larval stage of western rock lobster, which is thought to ensure high dispersal throughout the species range, and previous population genetic analyses based on allozymes. The focus of this project was to test the validity of this assumption. A secondary aim was to estimate the effective number of breeding adults, and hence determine the vulnerability of the stock to loss of genetic variation. Loss of genetic variation is a concern because it is associated with declines in reproductive capacity and the evolutionary potential of the species. Several recent studies have also shown declines in genetic diversity in commercially exploited species, even though the census population sizes (the total number of individuals) were very high. To achieve these aims we first had to develop specially designed genetic markers that would allow the measurement of genetic similarities between individuals collected from different locations within the fishery or between individuals collected at different times from the same location.We successfully developed 18 new genetic markers for the western rock lobster. Using these markers, and four additional markers that had been developed previously, we examined 631 individuals from eight locations in a survey of adult lobsters and 367 individuals from eight locations in the survey of new recruits. Our analyses revealed there were very small genetic differences between samples collected from different locations in the adults and no genetic differences between samples collected different locations in the new recruits. These results indicate that the breeding stock is a single population. By comparing new recruits collected in 2009 with those collected in the 1990s, we were also able to show that variation in the genetic markers has not changed over this time frame. These results suggest that the western rock lobster is in no danger of losing genetic diversity if current management practices and breeding stock sizes are maintained.