Age and growth of the blue stingray Dasyatis chrysonota chrysonota from the South-Eastern Cape coast of South Africa

Abstract

The age and growth of blue stingray Dasyatis chrysonota chrysonota from the south-east coast of South Africa was investigated by examination of bands on the vertebral centra. The annual nature of band deposition was verified by centrum edge characteristics and supported by growth of known-age individuals kept in captivity. The derived Von Bertalanffy parameters from age and length data were L ∞ = 532 mm (disc width, DW), K = 0.175 and t 0 = −3.65 for males and L ∞ = 913 mm DW, K = 0.070 and t 0 = −4.48 for females. Growth of three captive specimens showed distinct seasonal differences, with a mean growth rate of 7.3 mm·month−1 during summer and 3.8 mm·month−1 during winter. The mean rate of growth in captivity for the first year after birth (66.7 mm·year−1) is similar to the value obtained from back-calculations (64.6 mm·year−1), but higher than the calculated value of 45.1 mm·year−1. The estimated age at first maturity is five years for males and seven years for females.