Age, growth and maturity of the roundel skate, Raja texana, from the Gulf of Mexico, USA

Abstract

The roundel skate (Raja texana) inhabits near-shore waters throughout the Gulf of Mexico. Despite such a wide distribution, very little is known about its biology. In order to gain insight into the life history of this species, the age, growth and maturity of 231 skates ranging in size from 277 to 630-mm total length (TL) were examined. Based on vertebral band counts, the oldest age estimates obtained were 8 years for males and 9 for females, which corresponded to 495-mm TL and 630-mm TL respectively. Age-bias plots and coefficient of variation suggested that our ageing method represents a non-biased and precise approach to age assessment. Marginal increment and edge analyses suggested that growth bands are formed annually with a distinct trend of increasing growth at the beginning of March. Back calculations suggested a birth size of 113–118-mm TL. Observed and back-calculated length-at-age data were used to assess growth with four different models, including the von Bertalanffy (VBGM), von Bertalanffy with size at birth (VB with L 0), Gompertz and Francis models. Male and female growth was significantly different. The VBGM and the Francis model produced similar results and provided the best fit. Curves fitted with observed and back-calculated data suggested slightly faster growth than curves fitted with only observed data. Maturity occurred at 444-mm TL and 4.95 years for males, whereas females matured at 537-mm TL and 5.8 years.