Age and Growth of the Scalloped Hammerhead, Sphyrna lewini, in Northeastern Taiwan Waters

Abstract

Age and growth of the scalloped hammerhead, Sphyrna lewini,
\ncaught mostly by longline and harpoon in northeastern Taiwan waters from
\nDecember 1984 to November 1985, were determined from annulus counts from
\n325 individuals. Translucent and opaque zones on vertebral centra were formed
\ntwice a year, in June and December. The von Bertalanffy growth curve parameters
\nobtained using a nonlinear regression based on age and observed length
\nwere as follows: asymptotic length (Loo) = 319.72 cm total length (TL), growth
\ncoefficient (K) = 0.249, age at zero length (to) = - 0.413 yr for females; and
\nLoo = 320.59 cm TL, K = 0.222, to = - 0.746 yr for males. Growth was apparently
\nfast and varied among individuals. Growth rate s for females were estimated
\nto be 63cm for the first year, 23-50 cm/yr for years 2-5, and 3-19 cm/yr for years
\n6-13. Growth rates for males was 54 cm for the first year, 22-42 cm/yr for years
\n2-5, and 11-18 cm/yr for years 6-8. Holden's method was applied to estimate
\ngrowth parameters for purposes of comparison. Estimated age at maturity was
\n4.lyr (210cmTL) for females and-3:8yr (198cm-TL) for males, based on the von
\nBertalanffy growth equation from back-calculated data. The largest female (331
\ncm TL) whose age was determined in this study was 14.0 yr old; the largest male
\n(301 cm TL) was 10.6 yr old.