Total and organic mercury concentrations in the muscles of Pacific albacore (Thunnus alalunga) and bigeye tuna (Thunnus obesus)

•Some large BET had organic mercury concentrations exceeding 1μgg−1 wet weight.•Relationships between total/organic Hg concentrations and their size were found.•Muscle Hg bioaccumulation rates of BET were higher than those of ALB.•Young BET contain lower muscle total/organic Hg concentrations than same size of ALB.•Weekly dietary intakes of ALB/small BET for 340g, or of BET for 150g are suggested. Muscles of 115 North Pacific albacore (ALB, Thunnus alalunga) and 75 Pacific bigeye tuna (BET, Thunnus obesus), collected from 2001 to 2006, were analyzed. No ALB, but 13 large BET had organic mercury (OHg) concentrations exceeding 1μgg−1 wet weight. For both ALB and BET, total mercury (THg) and OHg concentrations were significantly and positively correlated with fork length (FL) and body weight. The muscle Hg bioaccumulation rates of BET were higher than those of ALB, particularly in the adult fish. Moreover, the lines had crossover points among the two species that imply the young BET (FL