Description: These data consist of both underway and station echosounder observations collected during the 2020 SUMMER (Sustainable Management of Mesopelagic Resources) Mediterranean cruise (30 September 2020 to 18 October 2020) on the RV Sarmiento de Gamboa. Narrowband (18, 38, 70, 120, 200 kHz) underway acoustic data were collected continuously using hull-mounted Simrad EK80 echosounders. The recording depths for the 5 frequencies were 1000, 1000, 750, 500, and 200 m respectively. Calibrations were carried out on the 1st of October 2020 using a 33 mm tungsten sphere,and the calibration results were applied to the instruments. During the survey, a Simrad wideband autonomous receiver (WBAT) was deployed down to a depth of 500 m whilst on station. In total, 31 drops were carried out at 5 stations. Four transducers (central frequencies were 45, 120, 200, 333 kHz) were operated using the WBAT in frequency modulated (FM) mode (bandwidth ranging from 45 to 445 kHz). The WBAT calibration data were collected using a 33 mm tungsten sphere. During the deployment of the WBAT, the hull-mounted EK80 was switched to FM mode to record broadband measurements. Raw power (W), number of transducer segments and transceiver impedance (Ohm) were stored in raw proprietary Simrad format (.raw, .idx).

Description: EK80 raw data were collected during the 2020 SUMMER (Sustainable Management of Mesopelagic Resources) Mediterranean cruise (30 September 2020 to 18 October 2020) carried out by RV Sarmiento de Gamboa. Five frequencies (18, 38, 70, 120, 200 kHz) were operated on continuous wave (CW) mode with specific settings by the hull-mounted EK80. A maximum volume of 100 MB of individual raw file was used. The recording depths for 5 frequencies from 18 to 200 kHz were 1000, 1000, 750, 500, and 200 m. The transmitted power for 5 frequencies from 18 to 200 kHz were set to 2000, 1000, 750, 250 and 150 W. Calibrations were carried out on the 1st of October 2020 using a 33 mm tungsten sphere, and the calibration results were applied to the EK80. Raw power (W), number of transducer segments and transceiver impedance (Ohm) were stored in raw proprietary Simrad format (.raw, .idx). The raw files were all recorded according to the UTC+00:00 time zone.

Description: The values of carbon remineralisation were measured in juveniles/adults of 5 non-migratory bristlemouth fishes (Cyclothone spp.) and partial migrator (Argyropelecus hemigymnus) sampled during the BATHYPELAGIC cruise (North Atlantic, June 2018). This dataset contains the values of numerical abundance, biomass, specific ETS activity, specific respiraton and respiration flux data analyzed from Northwest Africa (20° N, 20° W) to the South of Iceland. A. hemigymnus specimens were collected using a ''Mesopelagos” net (5 x7 m mouth opening, 58 m total length) equipped with graded-mesh netting (starting with 30 mm and ending with 4 mm) and a multi-sampler for collecting samples from 5 different depth layers (Olivar et al., 2017). However, Cyclothone specimens were collected using the Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS-1 m²) zooplankton net (Wiebe et al., 1985) with a 0.2 mm mesh size and with several nets for collecting samples from 8 different depth layers. The Mesopelagos catches were sorted out and identified on board to the lowest possible taxon, and specimens selected for Electron Transfer System (ETS) analyses were immediately frozen in liquid nitrogen for later analysis in the laboratory. MOCNESS samples were preserved in 5% buffered formalin, and specimens were sorted out later in the laboratory. Stomiiforms respiration in the meso- and bathypelagic zones of the ocean were estimated along the transect. Abundance, biomass, specific ETS activity, specific respiration and respiration are given by layer.

Description: Physical oceanography variables and carbon remineralisation (juveniles/adults of Cyclothone species and Argyropelecus hemigymnus) were analysed during the BATHYPELAGIC cruise (North Atlantic, June 2018). This dataset contains the depth, temperature, and conductivity which were recorded from surface to a maximum depth of 2000 m using a SeaBird SBE 25plus CTD equipped with a Seabird-43 Dissolved Oxygen sensor and a Seapoint Fluorometer. Values of numerical abundance, biomass, specific ETS activity, specific respiraton and respiration flux data analyzed from Northwest Africa (20° N, 20° W) to the South of Iceland are presented. A. hemigymnus specimens were collected using a ''Mesopelagos” net (5 x7 m mouth opening, 58 m total length) equipped with graded-mesh netting (starting with 30 mm and ending with 4 mm) and a multi-sampler for collecting samples from 5 different depth layers. However, Cyclothone specimens were collected using the Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS-1 m²) zooplankton net with a 0.2 mm mesh size and with several nets for collecting samples from 8 different depth layers. The Mesopelagos catches were sorted out and identified on board to the lowest possible taxon, and specimens selected for Electron Transfer System (ETS) analyses were immediately frozen in liquid nitrogen for later analysis in the laboratory. MOCNESS samples were preserved in 5% buffered formalin, and specimens were sorted out later in the laboratory. Stomiiforms respiration in the meso- and bathypelagic zones of the ocean were estimated along the transect. Abundance, biomass, specific ETS activity, specific respiration and respiration are given by layer between e.g. 100 m and 1000 m depth (MOCNESS net, 1900–1600 m, 1600–1300 m, 1300–1000 m, 1000–700 m, 700–400 m, 400–200 m, 200–100 m and 100–0 m; Mesopelagos, 1900–1200 m, 1200–800 m, 800–500 m, 500–200 m and 200–0 m).

Description: Depth, temperature, and conductivity were recorded during the Bathypelagic cruise (from 24th May to 23rd June 2018,) using a SeaBird SBE 25plus CTD, the dissolved oxygen with a Seabird-43 sensor both attached to an oceanographic rosette from surface to a maximum depth of 2000 m, and the fluorometer with a Seapoint sensor in the upper 200 m depth.

Description: The vertical distributions of early developmental stages of oceanic fishes were investigated across the tropical and equatorial Atlantic, from oligotrophic waters close to the Brazilian coast to more productive waters close to the Mauritanian Upwelling Region. Stratification of the water column was observed throughout the study region. Fishes were caught with a MOCNESS-1 net with mouth area of 1 m2 at 11 stations. Each station was sampled both during the day and at night within a single 24-h period. The investigation covered both larvae and transforming stages from the surface to 800 m depth. Distribution patterns were analysed, and weighted mean depths for the larvae and transforming stages of each species were calculated for day and night conditions. Forty-seven different species were found. The highest number of species occurred in the three stations south of Cape Verde Islands, characterized by a mixture of South Atlantic Central Water (SACW) and Eastern North Atlantic Central Water (ENACW). There was a marked drop in species richness in the three stations closer to the African upwelling, dominated by ENACW. The highest abundances occurred in the families Myctophidae, Sternoptychidae, Gonostomatidae and Phosichthyidae. Day and night vertical distributions of larvae and transforming stages showed contrasting patterns, both in the depths of the main concentration layers in the water column, and in the diel migration patterns (where these were observed). Larvae generally showed a preference for the upper mixed layer (ca. 0–50 m) and upper thermocline (ca. 50–100 m), except for sternoptychids, which were also abundant in the lower thermocline layer (100–200 m) and even extended into the mesopelagic zone (down to 500 m). Transforming stages showed a more widespread distribution, with main concentrations in the mesopelagic zone (200–800 m). Larvae showed peak concentrations in the more illuminated and zooplankton-rich upper mixed layers during the day and a wider distribution through the upper 100 m during the night. For most species, transforming stages were concentrated in the mesopelagic layers both day and night, although in some species (Diaphus cf. vanhoeffeni and Vinciguerria nimbaria), the transforming stages displayed vertical migration into the upper 100 m at night, in a manner similar to their adult stages.