We provide here a curated set of data containing representative fish length measurements. The specimens were collected by a Macroplankton trawl (~36 m² mouth opening, non-graded mesh with 3 mm light-opening) and a Harstad trawl from two expeditions across the Scotia Sea, Antarctica during austral summer (January-March) 2019. The collected material is obtained from standardized V-shaped hauls down to a maximum depth of ~200 m (Macroplankton trawl) and ~1000 m (Harstad trawl), although some shallower hauls are included either to look at vertically migrating adult mesopelagic fish that enter the epipelagic domain during nighttime hours, or because of depth restrictions due to shallow bottom topography. Lengths of fish are normally measured as total length (TL) from tip of snout to the end of the caudal fin ("untouched"), or as standard length (SL) from tip of snout to the posterior end of the last vertebra. The length measurement from the tip of the snout to the anal fin origin (preanal length, PAL) is used when the posterior part of the fish body is very thin and slender, thus impossible to determine the end of the "untouched" caudal fin or the bone knot of the caudal peduncle. Fish lengths were measured using an electronic caliper for the smallest larvae/juveniles, a fine line mm-ruler or a manual measuring board for the somewhat larger fish. The type of length measurement used is taxa specific. Sex of numerically abundant species where this has been possible to determine externally are also included (RV Kronprins Haakon only). These were the four species of myctophids (Electrona antarctica, Gymnoscopelus fraseri, Krefftichthys anderssoni, and Protomyctophum bolini) and sex was based on the presence of supra- and infracaudal luminous glands, or the shape of the antorbital luminous organ. Tissue samples for genetic analyses were obtained on an individual level and stored in 96% ethanol as the conservation medium.

This work was also financially supported by the Association of Responsible Krill Harvesting Companies (ARK; www.ark-krill.org).