Age and growth of Neotrygon picta, Neotrygon annotata and Neotrygon kuhlii from north-east Australia, with notes on their reproductive biology
Vertebral band formations were used to define age and growth in three Neotrygon species caught regularly as by-catch in prawn trawl fisheries in north-east Australia. Centrum edge and marginal increment ratio analyses were used to validate annual band formations. Age estimates ranged from 1 to 18 years, with the von Bertalanffy growth function considered to have the best fit to Neotrygon picta (males, WD∞ = 271 mm, k = 0·12; females, WD∞ = 360·5 mm, k = 0·08) and Neotrygon kuhlii (males, WD∞ = 438·6 mm, k = 0·08; females, WD∞ = 440·6 mm, k = 0·08) disc width (WD)-at-age data. The Gompertz growth function had the best fit to Neotrygon annotata WD-at-age data (males, WD∞ = 230·4 mm, k = 0·20; females, WD∞ = 265·5 mm, k = 0·31). Age at sexual maturity ranged from 3 to 6 years, with N. picta having the smallest size at birth (100 mm WD), smallest WD at 50% maturity (WD50: male, 172 mm, female, 180·7 mm) and lowest age at sexual maturity (3–4 years). This study helps redefine and improve the accuracy of fisheries-based risk assessments for these small species with relatively conservative life-history variables.
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