Mercury and selenium concentrations in sharks from northern Australian waters

Abstract

Total mercury, alkyl mercury and selenium concentrations in the muscle tissue of 15 carcharhinid (Carcharhinus sp., C. limbatus, C. sorrah, C. fitzroyensis, C. amblyrhynchoides, C. melanopterus, C. cautus, C. amboinensis, C. macloti, C. dussumieri, C. brevipinna, Rhizoprionodon acutus, R. taylori, Galeocerdo cuvieri, Negaprion acutidens) and three hammerhead (Sphyrna lewini, S. mokarran and S. blochii) sharks from northern Australian waters are reported. Total mercury concentrations ranged widely with maximum individual concentrations exceeding 1.5 mg kg^-1 wet weight in 11 species and values of over 3.0 mg kg^-1 in Carcharhinus sp., C. amblyrhynchoides, C. melanopterus, C. amboinensis and S. mokarran. Much of the variability in total mercury concentration was attributable to differences in length. Total mercury was adequately correlated with fork length by the power function relationship. There were signficiant differences in these relationships for males and females of six species: males had higher concentrations of mercury than females of the same size. Weighted mean mercury concentrations were calculated using species and size composition data from commercial feasibility fishing trials. Weighted means for species other than C. sorrah, C. macloti, C. brevipinna and C. dussumieri were greater than 0.5 mg kg^-1 and the value for the combined catch of all species was 1.22 mg kg^-1. Alkyl mercury comprised over 80% of the total mercury content in the muscle tissue. Maximum individual selenium concentrations were greater than 1.0 mg kg^-1 in nine species and the maximum concentration recorded was 3.4 mg kg^-1 for C. dussumieri. There were no obvious or consistent relationships between selenium concentration and fork length or between selenium and mercury concentrations.