Mercury concentrations in four carcharhinid and three hammerhead sharkes from coastal waters of the Northern Territory

Analysis of mercury in muscle tissue of four species of carcharhinid shark (genus Carcharhinus) and three species of hammerhead shark (genus Sphyrna) from coastal waters of the Northern Territory has indicated that each of the species studied accumulates relatively high concentrations of mercury. Maximum observed concentrations in all species except C. sorrah (Valenciennes) exceeded 1.5 mg kg-1. Concentrations greater than 4 mg kg-1 were recorded in C. amblyrhynchoides (Whitley), S. lewini (Griffith & Smith) and S. mokarran (Ruppell). Mercury concentration was highly dependent on shark size and increased more or less exponentially with length. Apart from S. lewini and S. mokarran, there were significant differences between length-mercury relationships for males and females of each species. At a given length, males tended to have accumulated higher concentrations of mercury than females. With the exception of C. sorrah, weighted mean concentrations of mercury for each species exceeded the current National Health and Medical Research Council standard for mercury of 0.5 mg kg-1. Implications of possible management based on mercury standards are considered using information available for C. limbatus (Valenciennes) and C. sorrah.