Methodology:

An RMT25 net was used to sample the mesopelagic fish, squid and macrozooplankton community during the survey DY090 in the Benguela Current region. 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 750-500m, 500-250m in one deployment and 250-125m and 125-10 m in an accompanying second deployment. Samples were collected across four time stations, three at location BN (BN1-3; 18.08°S 11.02°E) and one at location BS (BS1; 21.68°S, 9.54°E). At each time station, one set of deployments was undertaken during the hours of darkness and one in daylight. In total, the dataset comprises the catches of 16 separate deployments. The RMT25 was operated via a downwire net monitor and was equipped with a flow meter, and temperature and salinity sensors. Each depth interval in the deep deployment (between 750 m and 250 m) were sampled for approx. 40 mins while each in the shallow deployment (between 250 m and 10m) were sampled for approx. 20 minutes. The ship maintained a speed of 2 knots during both sets of deployments.

When retrieved, the total weight of each RMT25 net catch 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. In cases of high abundance of a particular taxon, sub-samples were extracted, weighed and enumerated 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 recorded directly after the catch was sorted on board.

Data collection:

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

2. Motion-compensated weighing scales

3. Volumetric flasks

4. Sorting trays and forceps

5. Binocular microscope

Data quality:

All taxa 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 abundance and combined wet weight of all taxa above ~4 mm were recorded, either to species or the next lowest taxonomic level feasible. The absence of any taxon from the datasheet indicates that it was not present in the respective catch.