Age and growth parameters for three heavily exploited shark species off temperate eastern Australia

The removal of large predatory sharks from the world's oceans poses profound threats to marine community structure and species conservation. Effective management of exploited shark stocks requires a sound understanding of the life histories of target species. Here we provide the first assessment of age and growth for Carcharhinus brevipinna in Australian waters, and for C. obscurus and C. plumbeus in eastern Australian waters, based on interpretations of vertebral growth bands. In doing so, we provide arguably among the most robust growth parameters to date for the abovementioned taxa on the bases of genetic validation and sample size and distribution, but acknowledge equally a range of limitations - most notably those associated with vertebral ageing and our lack of age validation. Comparatively, the three species displayed both contrasts and consistencies in their growth characteristics off Australia's southeast coast. For all three sharks, rates of growth were greatest in the years immediately after birth, males grew more rapidly than females in the juvenile phase, and females were observed to grow larger, live longer and were generally larger at any given age. Longevity and all modelled growth parameters (L_∞, k and L₀), however, differed among the three species, and appeared to challenge the findings for conspecific populations in other parts of the world. The validity of these latter comparisons is, however, compromised by a range of confounding factors. Nevertheless, we provide the least conservative k estimates for C. obscurus and C. plumbeus of those previously reported, and extend maximum age estimates for C. brevipinna. In this way, our results have important implications for the assessment of natural mortality, productivity, and hence resilience to stock depletion, in these species in southeastern Australian waters.