Individual carbon and nitrogen stable isotope compositions of sixteen deep pelagic fish species from the Bay of Biscay, Northeast Atlantic

The dataset contains individual carbon and nitrogen stable isotope compositions (δ13C and δ15N values, respectively) measured on 605 individuals belonging to 16 deep pelagic fish species (Arctozenus risso, Argyropelecus olfersii, Benthosema glaciale, Cyclothone spp., Lampanyctus crocodilus, Lampanyctus macdonaldi, Lestidiops sphyrenoides, Maulisia argipalla, Maurolicus muelleri, Melanostigma atlanticum, Myctophum punctatum, Notoscopelus bolini, Notoscopelus kroyeri, Searsia koefoedi, Serrivomer beanii, Xenodermichthys copei) collected on the Bay of Biscay slope, Northeast Atlantic. Fish sampling was carried out by pelagic trawl in canyons of the continental slope of the Bay of Biscay during EVHOE scientific cruises ("Evaluation Halieutique de l'Ouest de l'Europe"; https://doi.org/10.18142/8) in fall 2021. Trawls were conducted at night between 25 m and 1335 m depth at 7 stations. Each haul was conducted at a selected depth. Once the trawl reached the selected depth, it was towed horizontally (i.e. constant depth) at 4 knots for 1 hour. The average vertical mouth opening was about 24 m and the horizontal opening was about 58 m. Sub-samples for stable isotope analyses were taken from the white dorsal muscle. Small individuals of the same size sampled during the same trawling operation were grouped to have sufficient material for isotopic analyses. Analyses were performed using an isotope ratio mass spectrometer (Delta V Advantage with a Conflo IV interface, Thermo Scientific) coupled to an elemental analyser (Flash EA, 2000; Thermo Scientific). Results are presented in the usual δ notation relative to the deviation from international standards (PDB for δ13C values, atmospheric nitrogen for δ15N values), in parts per thousand (‰). Based on repeated measurements of USGS-61 and USGS-62, used as internal laboratory standards, the experimental analytical precision was <0.15‰ for both δ13C and δ15N values. As lipids are highly depleted in 13C, variations in δ13C values can occur between species with very different lipid contents while their food may be similar, biasing the interpretation of δ13C values. To mitigate this bias, individuals with a high lipid content (i.e. C:N > 5) were treated to remove lipids (see methodology Loutrage et al., 2024).