Methodology:

All fish were collected during the 2019 IMR-PINRO Barents Sea Ecosystem Survey. Cruise report containing full details of cruise stations, together with full details of environmental conditions and ecosystem context is linked in the Related URL section.

On board ship, fish were weighed and length measured. 1 cm^3 section of while muscle was excised from the dorsal musculature above the lateral line, wrapped in pre-labelled tin foil and immediately frozen at -20 degrees. In the case of small fish, whole fish were frozen and sub-sampled in the laboratory. Jellyfish bell tissue was excised on board or whole jellyfish bells frozen and subsampled in the laboratory.

Otoliths were removed from a sub-sample of fishes onboard ship, manually cleaned and placed in cell culture trays.

Muscle tissues were not lipid extracted prior to analyses. Frozen muscle was freeze dried, crushed in an agate pestle and mortar and approximately 0.3-1mg of muscle powder accurately weighed into tin boats prior to introduction to the mass spectrometer.

Otoliths were cleaned (if necessary) by wetting and manually removing any adhering tissue.

Otoliths were mounted whole onto glass slides, sulcus side upwards and approximately 50 micrograms of powder was excised from the sulcal ridge using a Dremel hand engraving tool with a cylindrical diamond-tipped drill bit. Powders were transferred to borosilicate vials prior to analysis. Approximately 0.3-0.5 micrograms of powder was accurately weighed into analysis vials for introduction to the mass spectrometer.

Maturity was assessed by IMR Norway and is included in this dataset where known.

Data collection:

CNS isotope values were determined using an Elementar visIon Isotope ratio mass spectrometer coupled to an EA elemental analyser.

Otolith CO isotope data was determined on a Thermo Finnegan MAT253 mass spectrometer coupled to a Kiel carbonate device.

Data quality:

Isotope mass spectrometers were calibrated against international reference standards, and accuracy and precision monitored through replicated analyses of internal standard materials (homogenised cod muscle for CNS data and powdered homogenised otolith for otolith d13C, d18O values.

Long term precision assessed as standard deviation of replicate analyses of internal standards (as unknown samples) was 0.15per-mille for d15N, 0.08per-mille for d13C and 0.5per-mille for d34S, and <0.1per-mille for both d13C and d18O values of otolith carbonate.