The life histories of endangered hammerhead sharks (Carcharhiniformes, Sphyrnidae) from the east coast of Australia


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The life histories of two globally endangered hammerhead sharks, Sphyrna lewini and Sphyrna mokarran, were examined using samples collected from a range of commercial fisheries operating along the east coast of Australia. The catch of S. lewini was heavily biased towards males, and there were significant differences in von Bertalanffy growth parameters (L and k) and maturity [stretched total length (LST) and age (A) at which 50% are mature, LST50 and A50] between those caught in the tropics (L = 2119 mm, k = 0·163, LST50 = 1471 mm, A50 = 5·7 years) and those caught in temperate waters (L = 3199 mm, k = 0·093, LST50 = 2043 mm, A50 = 8·9 years). The best-fit estimates for a three-parameter von Bertalanffy growth curve fit to both sexes were L = 3312 mm, L0 = 584 mm and k = 0·076. Males attained a maximum age of 21 years and grew to at least 2898 mm LST. The longevity, maximum length and maturity of females could not be estimated as mature animals could not be sourced from any fishery. Length at birth inferred from neonates with open umbilical scars was 465–563 mm LST. There was no significant difference in length and age at maturity of male and female S. mokarran, which reached 50% maturity at 2279 mm LST and 8·3 years. Sphyrna mokarran grew at a similar rate to S. lewini and the best-fit estimates for a two-parameter von Bertalanffy equation fit to length-at-age data for sexes combined with an assumed mean length-at-birth of 700 mm were L = 4027 mm and k = 0·079. Females attained a maximum age of 39·1 years and grew to at least 4391 mm LST. The oldest male S. mokarran was 31·7 years old and 3691 mm LST. Validation of annual growth-band deposition in S. mokarran was achieved through a mark, tag and recapture study.