Stock structure and effective population size of the commercially exploited Gummy shark

The Australian Gummy shark (Mustelus antarcticus) is the main target species of a large fishery that functions across its distribution in Southern and Eastern Australian waters. Commercial harvest of the species is currently considered sustainable based on target biomass estimates that show recovery from past overexploitation. However, previous research regarding stock structure have garnered conflicting results on the genetic structure of the species, necessitating further investigation to better inform fisheries management. Here, we evaluate the genetic structure and effective population size (Ne) of the Gummy shark using genome-wide single nucleotide polymorphisms (SNPs). We identified two distinct genetic clusters, one on the East coast, and one along the South coast. Moderate genetic differentiation was identified between each cluster, while within-cluster comparisons were largely admixed. Spatial analyses revealed some evidence for natal philopatry but no compelling evidence of isolation by distance. In addition, demographic modelling of each cluster showed a comparatively rapid decline of estimated Ne in the most recent past when compared to more historical projections, although current estimates are still considered high. These findings elucidate the current genetic structure of Gummy sharks and estimate the potential impact on Ne that overfishing can generate for the species.