MERCURY SPECIATION IN TUNA FROM THE NORTH PACIFIC OCEAN

Humans are exposed to toxic methylmercury (MeHg) principally by eating seafood, particularly canned and fresh tuna. However, the source (anthropogenic vs. natural, coastal vs. pelagic) of the MeHg that accumulates in marine piscivores such as tuna remains largely unknown. To address this paucity of knowledge, we are investigating the accumulation, speciation, and isotopic composition of mercury in three species of tuna that have different feeding behaviors (albacore Thunnus alalunga, yellowfin T. albacares, and Pacific bluefin T. orientalis). Both white and red hypaxial muscle were sampled from 34 tuna (1–2 y old, 63–94 cm fork length) caught by recreational anglers off the coast of San Diego, CA, during 2008–2011, and analyzed for total mercury and MeHg. Preliminary results suggest that there are considerable differences in MeHg accumulation between tuna species and that nearly all of the mercury in the muscle of these fish is as MeHg. Ongoing measurements of mercury, carbon, and nitrogen stable isotopes will help reveal whether interspecies variations of MeHg levels may be related to differences in either foraging behavior or sources of MeHg to the ocean and marine food web.