Life in the Slow Lane: Ecology and Conservation of Long-Lived Marine Animals

Demographic Analysis of the Dusky Shark Fishery in Southwestern Australia

Colin A. Simpfendorfer

doi: https://doi.org/10.47886/9781888569155.ch11

Abstract. —An assessment of the dusky shark Carcharhinus obscurus fishery in southwestern Australia was undertaken using demographic techniques. Current annual catches of C. obscurus by the fishery are 500–700 metric tons (live weight), most of which are recently born individuals (age-0). The best estimates of life history parameters indicate that the annual rate of population increase is 4.3% when unfished and that the F _MSY is 0.021. Tests indicate that the results are most sensitive to changes in values of natural mortality and age at maturity. Changes to the values of average litter size, reproductive periodicity, and longevity had little effect on the results. The inclusion in the analysis of age-specific exploitation rates from a tagging study indicate that at current levels of fishing the C. obscurus population in southwestern Australia is most likely to be sustainable. However, it must be noted that there is some unquantified mortality of older year-classes due to fishing operations outside of the managed fishery. The results indicate that it is possible to exploit long-lived, late-maturing, slow-reproducing marine animals by targeting the youngest age-classes. The results are discussed in relation to the dusky shark fishery in southwestern Australia and the exploitation of other long-lived marine species.