Population structure of Ballot's saucer scallop (Ylistrum balloti) for the east coast of Queensland

Abstract

Ballot's saucer scallops (Ylistrum balloti) are harvested by the east coast otter trawl fishery and contribute a higher proportion of the overall yearly catch than the co-located mud scallop (Amusium pleuronectes). Recent estimates of Ballot's saucer scallop biomass are below the defined limit reference point (20%), and the fishery is currently closed across much of its area (limited fishing is allowed in the southern offshore management region). An underlying assumption for fishery management is that Ballot's saucer scallops along Queensland’s east coast are one population to be managed and assessed as a single biological stock. Significant aggregations of Ballot's saucer scallops have been detected in the central trawl management region despite the low biomass estimates. Trawl fishery representatives have concerns about the single stock approach. Their observations of morphometric and colour differences between Ballot's saucer scallops from the central trawl management region and the management regions to the south are suggestive of distinct populations. To determine the population structure Fisheries Queensland used High Throughput Sequencing to identify 3217-5754 Single Nucleotide Polymorphisms (SNPs). The results indicated small (FSTs ~ 0.005), but significant (p<0.001) differences between scallops either side of 22 degrees South and was further supported by PCA, AMOVA and Admixture analyses. The study shows the existence of two populations of Ballot's saucer scallops on the east coast of Queensland.