Bioaccumulation and biomagnification of mercury and methylmercury in four sympatric coastal sharks in a protected subtropical lagoon.

Mercury bioaccumulation is frequently observed in marine ecosystems, often with stronger effects at higher trophic levels. We compared total mercury (THg) and methylmercury (MeHg) from muscle with length, comparative isotopic niche, and diet (via δC and δN) among four sympatric coastal sharks in Florida Bay (USA): blacknose, blacktip, bull, and lemon. Mercury in blacknose and blacktip sharks increased significantly with size, whereas bull and lemon sharks had a high variance in mercury relative to size. Both δC and δN were consistent with general resource use and trophic position relationships across all species. A significant relationship was observed between δC and mercury in blacktip sharks, suggesting an ontogenetic shift isotopic niche, possibly a dietary change. Multiple regression showed that δC and δN were the strongest factors regarding mercury bioaccumulation in individuals across all species. Additional research is recommended to resolve the mechanisms that determine mercury biomagnification in individual shark species.