In 2018, white muscle samples were collected from the lateral musculature of a random sample of up to 4 fish from each survey station of the International Pacific Halibut Commission's Fishery Independent Setline Survey (total n = 1653). Muscle samples were stored at -20°C, thawed, oven-dried to a constant mass at 42°C, and ground to a fine powder. Approximately 0.5 to 1.0 mg of each powdered sample was loaded into a tin capsule for stable isotope analysis. d¹³C and d¹⁵N values were determined using a Carlo Erba 1110 Elemental Analyzer (Carlo Erba Reagents, CE Instruments, ThermoQuest Italia S.p.A. Milan, Italy) coupled to a Thermo Delta Plus XP IRMS (Thermo Finnigan, Bremen, German) at the University of Wyoming’s Stable Isotope Facility (Laramie, Wyoming, USA). Long-term analyses of quality control standards have yielded precisions of 0.3‰ for d¹³C and 0.4‰ for d¹⁵N. Stable isotope data are presented in ‰ relative to Pee Dee Belemnite for ¹³C and atmospheric nitrogen for ¹⁵N.

Muscle samples were stored at -20°C, thawed, oven-dried to a constant mass at 42°C, and ground to a fine powder. Approximately 0.5 to 1.0 mg of each powdered sample was loaded into a tin capsule for stable isotope analysis. d¹³C and d¹⁵N values were determined using a Carlo Erba 1110 Elemental Analyzer (Carlo Erba Reagents, CE Instruments, ThermoQuest Italia S.p.A. Milan, Italy) coupled to a Thermo Delta Plus XP IRMS (Thermo Finnigan, Bremen, German) at the University of Wyoming’s Stable Isotope Facility (Laramie, Wyoming, USA). Long-term analyses of quality control standards have yielded precisions of 0.3‰ for d¹³C and 0.4‰ for d¹⁵N. Stable isotope data are presented in ‰ relative to Pee Dee Belemnite for ¹³C and atmospheric nitrogen for ¹⁵N.