This data set has biological measurements and stomach content analysis for fourteen specimens of Centrolophus niger which were frozen whole at sea during the Icelandic part of the International Ecosystem Summer Survey in Nordic Seas (IESSNS) in July 2017 and July 2021. In 2017, three specimens were collected to confirm species identification by a specialist at home institute. In 2021, all caught specimens were collected for detailed biological study. The C. niger were by-catch in a scientific pelagic ecosystem survey which includes trawling, cod-end mesh size 50 mm, in the surface layer, trawl headline visible in surface and foot rope at approximately 35 m depth. On December 1st, 2021, total weight of specimens was measured frozen and again thawed, thawed 16 hours at 0 °C. Length was measured to the nearest mm, weight to nearest 0.01 g, sex labelled as unidentified when macroscopic examination of gonads was inconclusive, maturity scale was mature, immature, or unidentified when macroscopic examination was inconclusive. Stomach, cut at oesophagus and pyloric caecae, was weighted with prey content intact and after prey was squished out of stomach. Otoliths were collected from each specimen. For detailed information about the surveys see the cruise reports attached to the campaigns. The data is provided by the Marine and Freshwater Research Institute (MFRI) in Iceland.