Individual carbon and nitrogen stable isotope compositions with length, weight, and trawling depth for twelve deep pelagic fish species from the Bay of Biscay, Northeast Atlantic, between 2007 and 2021.

The dataset contains individual carbon and nitrogen stable isotope compositions (δ13C and δ15N values, respectively) measured on 682 individuals belonging to 12 deep pelagic fish species (Aphanopus carbo, Arctozenus risso, Argyropelecus olfersii, Lampanyctus crocodilus, Lampanyctus macdonaldi, Melanostigma atlanticum, Myctophum punctatum, Notoscopelus kroyeri, Searsia koefoedi, Serrivomer beanii, Stomias boa, Xenodermichthys copei) collected on the Bay of Biscay slope, Northeast Atlantic. Individuals of all the species considered cover a wide range of lengths and weights. These parameters are reported individually as well as the trawling depth. 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) between 2007 and 2021. Trawls were conducted at night between 25 m and 2000 m depth at 17 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 (n= 682). In order to have sufficient material for isotopic analyses, small individuals belonging to the same size range and sampled in a similar depth range were pooled. 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. Because lipids are highly depleted in 13C relative to other tissue components (DeNiro and Epstein, 1977), significant variations in lipids (especially among species) can affect δ13C values even if trophic sources are similar. For part of the samples, measures were thus acquired on bulk (untreated) muscle samples and/or on delipidated samples (especially for samples prior to 2017 and/or fatty samples) using cyclohexane as the solvent to extract lipids, as described in Chouvelon et al. (2011). For these samples, both δ13C and δ15N values are thus indicated when available, showing no effect of cyclohexane on δ15N values but only on δ13C values when appropriate. With the elemental analyser, bulk C:N ratios measured on samples could be also determined and indicated. Indeed, bulk C:N ratios may be used as a proxy of the lipid content or body condition of organisms, especially in fish (Post et al., 2007; Hoffman et al., 2015) and can thus help identify potential fatty species and/or individuals needing lipid extraction and/or mathematical corrections for δ13C values (e.g. when C:N ratio is >3.5 in aquatic samples; Post et al., 2007).