Age and growth of the endangered Maugean skate (Zearaja maugeana) by using microchemical analysis

Context The Maugean skate (Zearaja maugeana) is an endangered species micro-endemic to two small embayments in western Tasmania, Australia. Given the species’ range restriction, status and exposure to large environmental variability, emerging impacts from anthropogenic pressures are likely to cause additional stress to the population. Information on Maugean skate age and growth is limited. Aims To determine the age and estimate growth parameters of the Maugean skate using vertebral banding patterns supplemented with microchemical analysis. Methods This study estimated the ages of opportunistically sampled Maugean skate (n = 44) from Macquarie Harbour between 2012 and 2019, by using incremental banding in their vertebrae. A multi-model inference framework using Akaike’s information criterion corrected for small sample size was used to determine the best fit growth function base on length at age data. Annual periodicity of growth bands was indirectly verified using laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) measuring the uptake of heavy metals in the vertebrae. Key results Age estimates ranged from 2 to 10 years. A two-parameter von Bertalanffy growth function provided the best fit when applied with a fixed length at birth on the basis of two neonate individuals (L0 fixed at 103.50-mm total length, TL), with the parameters as follows: the theoretical maximum length (L∞) and growth coefficient (k) estimated at 843.53 mm TL and 0.27 for females, 747.47 mm TL and 0.32 for males and 836.34 mm TL and 0.25 for pooled data. Females grew faster and reached a larger size than did males. Conclusion The Maugean skate’s reasonably fast growth, early maturity and short lifespan may help it withstand disturbances in the dynamic harbour. However, density-dependent responses to population declines could limit its ability to regulate numbers, especially amid ongoing threats. Implications The use of archived samples of vertebrae indirectly verified with microchemistry demonstrates a novel technique to describe the age and growth of Maugean skate, and provides critical life-history parameters to contribute to population assessments of this endangered population. The need to carry out age-validation studies for this species is also highlighted.