Comparative rates of growth of the Port Jackson shark throughout its southern Australian range

Abstract

Port Jackson sharks are distributed throughout southern Australia, with evidence suggesting that potential subpopulations exist. If subpopulations are evident, then phenotypic variation among groups should result in differences in life-history parameters. The present study tested for patterns of spatial variability of life-history parameters among regional Port Jackson shark populations. Rates of growth from Port Jackson sharks caught in the gulf waters of South Australia were calculated on the basis of counts of vertebral increments. Growth parameters were obtained by fitting the length-at-age data to von Bertalanffy and Gompertz growth functions. While the derived growth curves fit the length-at-age data well (r2 ranged from 0.87 to 0.91), parameters showed considerable differences between the two functions, with the von Bertalanffy function providing the more realistic estimates of growth (combined sexes: k = 0.081 year–1, L∞ = 1232 mm total length and t0 = –1.937 years). Life-history parameters for South Australian Port Jackson sharks were collated with the available data for the species, facilitating comparisons among regional populations. Growth curves among populations varied significantly; however, considerable overlap in the length ranges of size at birth and sizes at maturity among populations were evident. Overall, the data presented here do not provide definitive support for the presence of subpopulations across the distribution of the Port Jackson shark, suggesting that molecular analysis maybe required to directly test for structuring.