Stable isotope ratios and mercury levels in red meat products from baleen whales sold in Japanese markets

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We analyzed the δ13C, δ15N and δ18O values and Hg concentration in red meat products originating from the predominant types sold in Japan for human consumption: two populations of common minke (J- and O-types), Bryde's and sei whales in the western North Pacific Ocean, and fin and Antarctic minke whales in the Southern Ocean. The order of the trophic positions, evaluated by δ15N values and Hg concentrations, coincided with their known feeding habits: common minke (J-type)=common minke (O-type)>Bryde's≥sei≥Antarctic minke≥fin. The Hg concentrations in the combined samples from the six samples were significantly correlated with their δ15N values (γ=0.455, n=66, p<0.05), reflecting overall differences in the trophic level. This correlation was not significant for within-species comparison for the common minke (J- and O-types) or the Bryde's whale, probably reflecting the higher δ15N value and lower Hg concentration in the North Pacific Ocean around Japan. Determination of δ13C, δ15N and δ18O could be used to discriminate between the red meat products originating from the whale species in the North Pacific and Southern Oceans. However, the four whale species or populations in the Pacific Ocean could not be discriminated on basis of these values, nor could the two species in the Southern Ocean. Positive correlations between the δ13C and δ15N values and negative correlations between the δ15N and δ18O values and the δ13C and δ18O values, probably reflecting migration patterns, were found in some whale species in the North Pacific and Southern Oceans.