Nearshore Fish Isotope Values, Beaufort Sea, Alaska, 2017-2019

Fyke nets were deployed in water ~1 m deep, up to 50 m from shore, and sampled every 24 h. Most fish captured in fyke nets were released live after identification, counting, and measurement, with a subset saved for this study. Beam trawls (1 m or 3 m) were opportunistically deployed in 2017 and 2018 near the fyke net stations to ensure fish using habitat away from the shoreline were represented in this analysis.

Fish were stored frozen at -20 °C prior to laboratory work. In the laboratory, each fish was thawed and measured to the nearest mm. Length was measured from the tip of the snout to the fork of the tail (fork length), or to the end of the tail for species without forked tails (total length). Following length measurement, an epaxial muscle sample was collected for stable isotope analysis and kept frozen at -20 °C. Muscle samples were freeze-dried for at least 48 hours and homogenized by grinding to a fine powder with a mortar and pestle. Approximately 1 mg of sample was weighed into tin cups. Analysis was performed at the University of Texas at Austin Marine Science Institute core facilities in Port Aransas, Texas, USA. A ThermoFisher Scientific EA-Isolink CNSOH Elemental Analyzer (Waltham, Massachusetts, USA) coupled to a ThermoFisher Scientific Delta V isotope ratio mass spectrometer in continuous-flow (He) mode was used to determine fish muscle carbon and nitrogen isotopic compositions. All values are reported in delta (δ) notation, relative to standards VPDB for δ13C and air for δ15N. Calibration of δ13C to VPDB and δ15N to air was achieved using standards USGS-40 (δ13C = -26.39 ‰; δ15N = -4.52 ‰) and USGS-41a (δ13C = 37.63 ‰; δ15N = 47.57 ‰). Accuracy was evaluated using a casein protein standard purchased from EA Consumables (Pennsauken, New Jersey, USA). Note: lipids were not extracted from tissue samples and a lipid correction factor has not been applied to values. Additional details are available in Stanek et al. 2022.

Freeze-dried epaxial muscle was combusted at 900 °C in evacuated, sealed quartz tubes in the presence of CuO. Following cryogenic purification, CO2 was reduced to graphite at 550 °C using the sealed tube Zn reduction method (Xu et al. 2007). 14C data are reported as fraction modern (F14C), radiocarbon age (14C Age), and as Δ14C, or the per mil deviation of the 14C/12C ratio in the sample from that of the oxalic acid standard (OX-I) decay-corrected to 1950 (Stuiver and Polach 1977). All 14C values reported are corrected for mass-dependent fractionation using the AMS in-line δ13C measurements.