Age, growth, and reproduction of the spinner shark, Carcharhinus brevipinna, in the northeastern waters of Taiwan

Abstract

Age, growth, and reproduction of the spinner shark, Carcharhinus brevipinna (Müller and Henle, 1938), are described from 383 specimens (193 females and 190 males) collected from Oct. 1995 to Sep. 1996 in waters off northeastern Taiwan. Annuli in precaudal vertebrae form once a year and numbered up to 21 and 17 for females and males, respectively. The von Bertalanffy growth parameters estimates, based on age and back-calculated length data, were as follows: asymptotic (L∞) = 288.2 cm total length (TL), growth coefficient (k) = 0.151/yr, age at 0 length (t0) = -1.988 yr for females; and L∞= 257.4 cm TL, k =0.203/yr, t0 = -1.709 yr for males. The growth rate for females was estimated to be 29.9 cm for the 1st year, and then decreased from 25.7 to 16.3 cm/yr for years 2~5, from 14.0 to 7.7 cm/yr for years 6~10, and from 6.6 to 1.7 cm/yr for years 11~20. Growth rate for males was 33.4 cm/yr for the 1st year, then decreased from 27.3 to 14.8 cm/yr for years 2~5, from 12.1 to 5.4 cm/yr for years 6~10, and from 4.4 to 0.7 cm/yr for years 11~20. The mean total lengths at maturity were estimated to be 222.5 and 220.5 cm for females and males, which corresponded to 7.8 and 7.9 yr, respectively. Evidence suggested a 2 yr reproductive cycle in females, with a gestation period of 10~12 mo. Carcharhinus brevipinna is viviparous, with a yolk-sac placenta. The number of embryos per litter (N) was 3~14 (mean, 8.5), and it increased with the size of the mother (N = -45.06 + 0.198TL). TL at birth was estimated to be 65~70 cm, and the sex ratio of embryos was 1: 1.