Age and Growth of the Dusky Shark, Carcharhinus obscurus, in the Western North Pacific Ocean

Abstract

Age and growth of the dusky shark, Carcharhinus obscurus, in the western North Pacific Ocean was estimated based on 434 specimens (213 females and 256 males) collected between September 2002 and November 2003 at the Nanfanao fish market, in northeastern Taiwan. Sex-specific relationships between body weight (W) and total length (TL) were estimated as follows: W = 2.03 × 10-6TL3.216 (n = 209, p < 0.01) for females and W = 8.01 × 10-6TL2.957 (n = 294, p < 0.01) for males. The relationship between TL and the vertebral centrum radius (R) for both sexes (“sexes-combined” data) was described using the following equation TL = 14.74 + 20.31R (n = 399, p < 0.01). Growth band pairs (including translucent and opaque bands) in precaudal vertebrae were determined to form once annually, based on centrum edge analysis and verified by statistical analysis. The maximum number of growth band pairs was 29 for females and 24 for males. The Robertson growth function best fit the observed length-at-age data. Sex-specific growth equations were not significantly different; thus, the combined growth parameters for both sexes were estimated as: asymptotic length (L∞) = 369.4 cm TL, b = 0.912, growth coefficient (kR) = 0.126 yr-1 (n = 385, p < 0.01). Age at maturity was estimated to be 16.6 yrs for females and 15.5 yrs for males.