Age and growth estimates of the whitespotted bamboo shark, Chiloscyllium plagiosum, in the northern waters of Taiwan

Abstract

Age and growth rates of the whitespotted bamboo shark, Chiloscyllium plagiosum, were described from 481 specimens (313 females and 168 males, 35.5-85.0 cm in total length) collected from Feb. 2002 to Feb. 2003 in waters off northern Taiwan on bottom longlines or lobster trap nets. The sex-specific relationships between weight (W) and total length (TL) significantly differed and could be expressed as: W = 1.64 x 10-3 TL3.15 (n = 313, p < 0.05) for females and W = 5.09 x 10-3 TL2.87 (n = 168, p < 0.05) for males. Age was determined using vertebral banding patterns. A single growth band (comprising translucent and opaque zones) is formed each year, with up to 7 bands observed for both sexes. A marginal increment ratio analysis indicated that the translucent zone formed from June to Sept. Four growth functions, the traditional von Bertalanffy (VBGF), VBGF with a fixed size-at-birth (L0), Gompertz, and Robertson functions were used to model the observed length-at-age data. The sex-specific growth equations significantly differed. The traditional VBGF, based on observed length-at-age data, predicted an asymptotic length (L∞) of 95.9 cm TL, a growth coefficient (k) of 0.205, a theoretical age at zero length (t 0) of -0.95 yr for females; and an L∞ of 100.9 cm TL, k of 0.198, t 0 of -0.90 yr for males. The parameters of VBGF with L0 set to 15.0 cm were estimated to be an of L∞ 93.2 cm TL and k of 0.224 for females; and an of L∞ 98.5 cm TL and k of 0.212 for males. Akaike, s information criterion showed that the VBGF with L0 had the best fit. Ages at maturity estimated from the VBGF with L0 were 4.5 and 4.4 yr for females and males, respectively.