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

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.

Automated summary

The study found that neonatal blacktip sharks primarily obtain mercury through maternal offloading, while juveniles mainly accumulate mercury through dietary exposure. Additionally, comparisons with previous surveys suggest that mercury levels in southwest Florida estuaries have not declined over the past two decades.