Biological aspects of juvenile great hammerhead sharks Sphyrna mokarran from the Arabian Gulf

Abstract

The life history of the critically endangered great hammerhead Sphyrna mokarran was examined using samples collected from commercial fisheries operating in Saudi Arabian waters of the Arabian Gulf. In all, 105 specimens (47 males, 58 females), with a total length (TL) ranging from 67.0 to 236.0cm, were examined between April 2016 and November 2019. All individuals were immature. A neonate measuring 67.0cm TL caught in early June suggested the parturition period of this species was during May and June. Vertebrae under the first dorsal fin from 69 individuals (30 males, 39 females) were processed. Three age groups, from 0+ to 2+ years old, were identified by vertebrae analysis. Based on the relationship between vertebral central diameter and TL, the Fraser–Lee approach was used to back-calculate the growth history of TL. A two-parameter von Bertalanffy growth function provided the best fit to describe early growth of great hammerheads during 0–2.9 years of age based on observed and back-calculated length-at-age data. The asymptotic lengths and k values were estimated to be 256.8cm TL and 0.449 year–1 respectively. This study provides the first life history information of great hammerhead sharks in the north-western Indian Ocean.