Age and growth estimates of the blue shark Prionace glauca in the central South Pacific Ocean

Abstract

The age and growth of the blue shark Prionace glauca in the central South Pacific is described based on 267 specimens that were collected by scientific observers on board Taiwanese large-scale tuna longline fleets between May 2009 and May 2011. Growth band pairs (identified as translucent and opaque bands) were counted on images photographed from X-ray films of the vertebrae from the caudal peduncle region. The marginal increment ratio and centrum edge analysis indicated that a growth band pair was formed on the vertebral centrum once per year. The band pairs after the birthmark were counted from 2 to 11 for females and from 2 to 15 for males. The bias corrected Akaike information criterion indicated that the von Bertalanffy growth function (VBGF) best fitted the observed total length (TL)-at-age data. The parameters of sex-specific VBGF were estimated as follows: for females, theoretical maximum length (L∞) mean ± s.d. = 330.4 ± 46.6 cm TL, growth coefficient k = 0.164 ± 0.057 year–1 and theoretical age at length 0 (t0) = –1.29 ± 0.78 years; for males, L∞ = 376.6 ± 32.6 cm TL, k = 0.128 ± 0.022 year–1 and t0 = –1.48 ± 0.54 years. The longevities were estimated to be at least 16.8 and 21.6 years for females and males respectively.