Nutrient concentrations in whole mesopelagic and ground fish from two campaigns (2005, 2010) in the Kerguelen area, southern Indian Ocean

The dataset contains dry weight nutrient concentrations (20 nutrients, calcium Ca, phosphorus P, sodium Na, potassium K, magnesium Mg, strontium Sr, iron Fe, zinc Zn, copper Cu, manganese Mn, selenium Se, arsenic As, nickel Ni, cobalt Co, molybdenum Mo, chromium Cr, cadmium Cd, vanadium V, silver Ag, lead Pb) measured on 264 individuals belonging to 34 forage fish species were collected during two ship-based sampling campaigns on and around the Kerguelen Plateau. The first sampling campaign took place on the eastern slope waters of the Kerguelen Islands (49°05’–49°20’S, 71°15’–72°15’E) on the 25 m-long La Curieuse vessel in January 2005, and aimed to sample the mesopelagic fauna. Fishing operations were carried out at night, with an International Young Gadoid Pelagic Trawl (IYGPT) with 12 m x 7 m opening and 10 mm cod-end mesh deployed for 30-min at constant speed, at depth varying from 50 to 425 m (Cherel et al. 2010, Duhamel et al. 2000). Most samples caught during this campaign (n = 167) were myctophids (n = 119). The second sampling campaign (named ’Poker 2’) took place from August to October 2010 on the 77 m-long trawler FV Austral. It focused on the demersal fauna and yielded the remaining 97 fish samples. Two hundred stations from shelf and deepsea habitats were sampled during 30-min day trawling operations using a bottom trawl (35 m headline/39 m footrope, reference: G2035013 from Le Drezen: www.ledrezen.com) with a 40 mm cod-end mesh (Duhamel et al. 2017). For both campaigns, fish were sorted on board after initial identification and then kept frozen at -20°C until processing. Identification was again confirmed before sample processing relying on fish external features using published guides (Hulley 1981) and our own reference collection. In 2021-2022, each fish was thawed, rinsed with ultrapure water, measured, weighed and ground in the laboratory in a clean and contamination-free setting before being stored at -20°C. All material was carefully rinsed with ultrapure water and ethanol between samples to avoid contamination. Samples were then freeze-dried for a minimum of 72 hours and ground to a fine powder until analysis. Total concentrations of major constitutive chemical elements in biological tissues (P, Ca, K, Na, Mg) were determined by inductively coupled plasma atomic emission spectrometry (ICP-OES, Vista-Pro Varian). Aliquots of samples (∼250 mg dry mass of homogenised powder) were digested using a 6:2 (v/v) mixture with nitric acid (HNO3 69%, Trace Metal Grade®, FisherScientific) and hydrochloric acid (HCl, 34%, Trace Metal Grade®, FisherScientific). Acidic digestion of the samples was performed over-night at room temperature and then in a microwave oven (START-D, Milestone). Finally, the digestats were diluted to 50 mL with ultrapure water before analyses with ICP-OES. Total concentrations of essential trace nutrients (As, Co, Cu, Fe, Mn, Ni, Se, Zn) were determined by inductively coupled plasma mass spectrometry (ICP-MS, ICAP-Qc ThermoFisher). Aliquots of samples (∼200 mg dry mass of homogenised powder) were placed in Teflon bombs and mineralized with a mixture of ultrapure HNO3 acid (PlasmaPure Plus grade, SCP Science®) and ultrapure water using a micro-wave (ETHOS-UP, Milestone). The digests were then diluted to 50 mL with ultrapure water before analyses with ICP-MS. The quality assurance of all metal analyses relied on blank and internal standard controls, and on the accuracy and reproducibility of data relative to the certified reference materials (CRMs) used in each analytical run. The CRMs used were TORT-3 (lobster hepatopancreas, National Research Council of Canada/NRCC) and DOLT-5 (dogfish liver, NRCC). Blank values were systematically below the detection limits, and CRM values concurred with certified concentrations and recovery rates ranged between 75% and 116% depending on the nutrients and the CRMs (they are provided in the dataset).