Mercury concentrations in Alaska Pacific halibut muscle relative to stable isotopes of C and N and other biological variables

Total mercury concentrations ([THg]), δ¹⁵N and δ¹³C values were determined in muscle of 693 Pacific halibut caught in International Pacific Halibut Commission setline surveys in Alaska (2002 − 2011). Project goals were to evaluate whether 1) δ¹⁵N and δ¹³C varied with region, age, sex and length of halibut, and 2) muscle [THg] varied with δ¹⁵N and δ¹³C (feeding ecology) while accounting for sex, length, and region. Variation in [THg] was explained, in part, by halibut feeding ecology as [THg] increased with trophic position (increasing δ¹⁵N). Halibut from the western Aleutian Island region were the exception, with overall lower δ¹⁵N values and significantly higher [THg] than halibut from other Alaskan waters. This [THg] pattern has been observed in other Aleutian biota, possibly the result of northeasterly atmospheric movement of mercury emissions from Asia and/or other local sources and processes. The significantly lower δ¹⁵N values for these halibut warrants further investigation of halibut prey. - Highlights: • Mercury, δ¹⁵N, and δ¹³C were determined in muscle of 693 Pacific halibut in Alaska. • Variation in muscle mercury level was explained, in part, by halibut feeding ecology. • Muscle mercury concentration generally increased with relative trophic position (δ¹⁵N). • Western Aleutian halibut had lower δ¹⁵N and higher mercury than other regions. • Assessment of mercury and trophic relationships accounted for sex, size, and region.