Methodology:

An RMT25 net was used to sample the mesopelagic fish, squid and macrozooplankton community during the survey DY086 at the sustained observation station P3 (52.70°S, 40.26°W) in the northern Scotia Sea, Southern Ocean. The RMT25 is a midwater trawl with a mouth area of 25 m2 and a variable mesh size, 18 mm reducing to 5 mm towards the cod-end. The RMT25 used in this instance had two separate nets allowing two different depth intervals to be sampled discretely. These intervals were set at 500-250 m and 250-10 m. Samples were collected across three time stations (P3 A, P3 B and P3 C) approximately 10 days apart. At each time station, one deployment was undertaken during the hours of darkness and one in daylight, making a total of 6 deployments over the entire cruise. The RMT25 was operated via a downwire net monitor and was equipped with a flow meter, and temperature and salinity sensors. Each depth interval was sampled for approximately 40 mins while the ship maintained a speed of 2 knots.

When retrieved, the total weight of each RMT25 net haul was initially recorded with a calibrated, motion compensated weighing scales before further taxonomic analysis. All fish, squid and macrozooplankton specimens were identified to species level, where possible, and the composite weight and numbers per species recorded. Where necessary, sub-samples of the total catch of a species were counted and then multiplied by the inverse of the sub-sample fraction to determine total numbers in the catch. After sorting, a sub sample of specimens were either frozen for stable isotope and lipid analysis at -80°C or flash-frozen in liquid nitrogen for ETS (details not recorded here).

The abundances and weights in the datasheets are those directly recorded after the catch was sorted on board. Subsequent dry weights were calculated based on wet weight to dry weight relationships, either reported in the literature or obtained from dry weight measurements on specimens retained from this cruise or similar cruises in this region (listed in datasheets).

Data collection:

1. An RMT25 trawl (25m2 mouth diameter, 5 mm minimum mesh size)

2. Motion-compensated weighing scales

3. Volumetric flasks

4. Binocular microscope

Data quality:

All species were identified according to the taxonomic guides available at time of analysis and the user must be aware that some species names may have since been updated.

The entire catch was sorted and all specimens above ~4 mm were recorded at least to a low taxonomic level. The absence of any taxon from the datasheet indicates that it was not present in the catch.