Assessment of biological reference points for management of the smooth hammerhead shark, Sphyrna zygaena, in the Northwest Pacific Ocean

Abstract

The smooth hammerhead shark, Sphyrna zygaena, a top marine predator, is one of the species commonly caught by the Taiwanese offshore shark fisheries. However, its stock status information is still very limited and management measures is difficult to implement. To understand its population dynamics, the yield-per-recruit analysis (YPR) and the spawning-per-recruit analysis (SPR) were used in this study to estimate the biological reference points (BRPs) and the population status of smooth hammerhead shark in the Northwest Pacific Ocean. The results of deterministic YPR analysis showed that the current fishing mortality (F_(cur)) was lower than the BRP of F_(0.1) for males but higher than F_(0.1) for females. Furthermore, results of the SPR analyses indicated that the current SPR (SPR_(cur)) was substantially lower than target reference points (SPR_(35%)) and threshold reference points (SPR_(30%)). This finding indicated that the smooth hammerheads stock of female in the Northwest Pacific Ocean is overexploited under current fishing level. It is suggested that the stock condition of scalloped hammerhead sharks should be constantly monitored to ensure their sustainability.