Age and growth estimates of the bigeye thresher shark, Alopias superciliosus, in northeastern Taiwan waters

Abstract

Age and growth of Alopias superciliosus in waters off northeastern Taiwan were determined from vertebral band counts on 321 specimens (214 females and 107 males) and verified with a length-frequency analysis of 821 specimens (491 females and 330 males). Growth bands formed once a year according to marginal increment analysis and numbered up to 21 and 20 bands for females and males, respectively. The parameters of von Bertalanffy growth equations estimated from vertebral readings were the following: asymptotic precaudal length (L∞) = 224.6 cm, growth coefficient (K) = 0.092/ yr, age at zero length (t(o)) = -4.21 yr for females; and L∞ = 218.8 cm, K = 0.088/yr, t(o) = -4.24 yr for males. The ages at maturity were estimated to be 12.313.4 yr for females, 9-10 yr for males. The largest female aged from vertebrae was 20 yr old, the largest male 19 yr old. Length-frequency analysis supported our vertebral ageing estimates.