Mercury in neonatal and juvenile blacktip sharks (Carcharhinus limbatus). Part I: exposure assessment

Abstract

Elasmobranchs are exposed to mercury (Hg) through a variety of pathways in the environment. This study assessed maternal offloading and diet-based Hg exposure for neonatal and juvenile blacktip sharks (Carcharhinus limbatus) from Charlotte Harbor located along southwest Florida’s coast, a recognized Hg hotspot. Neonates (n = 57) had highest total Hg (THg) concentrations in the kidney (0.56 ± 0.26 mg kg−1; n = 38) and muscle (0.53 ± 0.17 mg kg−1; n = 57), followed by liver (0.31 ± 0.11 mg kg−1; n = 38), and blood (0.05 ± 0.033 mg kg−1; n = 57). Juveniles (n = 13) exhibited a different distribution with highest THg in the liver (0.868 ± 0.54 mg kg−1; n = 6), followed by the muscle (0.84 ± 0.28 mg kg−1; n = 13), kidney (0.55 ± 0.22 mg kg−1; n = 6), and blood (0.11 ± 0.04 mg kg−1; n = 11). The distribution of THg among tissues and liver-to-muscle ratios indicated that Hg originated primarily from maternal offloading in neonates, whereas juveniles continued to accumulate Hg through dietary exposure post-parturition. Additionally, comparisons between results of the present study and previous Florida blacktip shark surveys suggested that Hg levels have not declined in southwest Florida estuaries for over two decades.