Description: We provide here a curated set of data containing standardized catch biomasses and abundances of key macroplankton and mesopelagic fish taxonomically identified to species or genera or the nearest possible taxonomic group collected by a Macroplankton trawl (~6 m x 6 m mouth opening, non-graded mesh with 3 mm light-opening) from cruises in the Norwegian Sea during the International Ecosystem Survey in the Nordic Seas (IESNS) in May to June 2019 and 2020. The collected material is obtained from standardized V-shaped hauls down to a maximum depth of about 1000 m, although some shallower V-hauls are included either to look at the vertically migrating mesopelagic organisms that enter the epipelagic domain during nighttime hours, or because of depth restrictions due to shallow bottom topography. This dataset holds the biomass and abundance data of species or taxonomically identified categories. Filtered water volume (m³) was determined by calculating the towed horizontal distance (m) from when the trawl was deployed until maximum depth (m) and similarly when retrieved. Then, knowing the maximum depth of the trawl, by trigonometric calculations the trawl path (hypothenuse) during downcast and upcast were derived. The filtered volume was calculated by multiplying the summed towpath distance (m) by the nominal trawl opening of 36 m².

Description: We provide here a curated set of data containing representative length/size measurements of key macroplankton and mesopelagic fish collected by a Macroplankton trawl (~6 m x 6 m mouth opening, non-graded mesh with 3 mm light-opening) from cruises in the Norwegian Sea during the International Ecosystem Survey in the Nordic Seas (IESNS) in May to June 2019 and 2020. The collected material is obtained from standardized V-shaped hauls down to a maximum depth of about 1000 m, although some shallower V-hauls are included either to look at the vertically migrating mesopelagic organisms that enter the epipelagic domain during nighttime hours, or because of depth restrictions due to shallow bottom topography.

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Melle, W., Klevjer, T., Strand, E., Wiebe, P. H., Slotte, A., & Huse, G. Fine-scale observations of physical and biological environment along a herring feeding migration route. Deep-Sea Research Part II: Topical Studies in Oceanography, 180, (2020): 104845, doi:10.1016/j.dsr2.2020.104845.

Description: We observed herring horizontal and vertical distribution during feeding migration along a 128 km transect across the Arctic front of the Norwegian and Iceland seas, in early June, in relation to its physical, chemical and biological environment, distribution of prey organisms and pelagic and mesopelagic competitors. The Norwegian Spring Spawning herring is one of the largest and economically most important stocks of pelagic fish in the world and understanding what controls its feeding migration is, and has been for centuries, a major research question that also has major implications for management. High resolution ecosystem data were obtained by hull mounted multi-frequency acoustics and a towed platform undulating between 10 and 400 m equipped with multi-frequency acoustics, temperature, salinity and fluorescence sensors, an Optical Plankton Counter and a Video Plankton Recorder. Additional sampling was done by MOCNESS, Macroplankton trawl, and CTD equipped with water bottles for temperature, salinity, nutrients and chlorophyll at discrete stations along the transect. Biological characteristics and stomach content of the herring were obtained from samples at discrete trawl stations. The Arctic front proved to be an important transitional zone in zooplankton biomass, abundance and diversity. Phenology of phyto- and zooplankton also changed across the front, being somewhat delayed on the cold side. The herring were distributed all along the transect showing a shallow distribution on the warm side and both deep and shallow on the cold side, not clearly related to light and time of the day. The herring stomach content was higher on the cold side. There was no significant pattern in average age, weight, or body length of the herring along the transect. The herring were present and fed in the area of the transect during the time when the overwintering generation of Calanus finmarchicus dominated, before the development of the new generation of the year. We suggest that the phenology of C. finmarchicus can be an important driver of the herring feeding migration. While prey-availability was higher on the Arctic side of the front, light conditions for visual feeding at depth were probably better on the Atlantic side. The herring did not show classical dial vertical migration, but its prey did, and the herring's prey were probably available within the upper 100 m during the course of a 24 h cycle. With a general westward direction of migration, the herring along the transect moved towards lower temperatures and temperature did not seem to be a probable driver for migration. We conclude that fine-scale studies of herring migration and feeding can increase our understanding of the migratory processes and add to our understanding of large-scale distributional patterns, changes therein, and herring trophodynamics and ecological role. The fine-resolution parameters can also be important as input to ecosystem models.

Description: We would also like to acknowledge the funding from Euro-BASIN, EU FP7, Grant agreement No 264933, HARMES, Research Council of Norway project number 280546 and MEESO, EU H2020 research and innovation programme, Grant Agreement No 817669.

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Melle, W., Klevjer, T., Drinkwater, K. F., Strand, E., Naustvoll, L. J., Wiebe, P. H., Aksnes, D. L., Knutsen, T., Sundby, S., Slotte, A., Dupont, N., Salvanes, A. G. V., Korneliussen, R., & Huse, G. Structure and functioning of four North Atlantic ecosystems - a comparative study. Deep-Sea Research Part II: Topical Studies in Oceanography, 180, (2020): 104838, doi:10.1016/j.dsr2.2020.104838.

Description: The epi- and mesopelagic ecosystems of four sub-polar ocean basins, the Labrador, Irminger, Iceland and Norwegian seas, were surveyed during two legs from Bergen, Norway, to Nuuk, Greenland, and back to Bergen. The survey was conducted from 1 May to 14 June, and major results were published in five papers (Drinkwater et al., Naustvoll et al., Strand et al., Melle et al., this issue, and Klevjer et al., this issue a, this issue b). In the present paper, the structures of the ecosystem are reviewed, and aspects of the functioning of the ecosystems examined, focusing on a comparison of trophic relationships in the four basins. In many ways, the ecosystems are similar, which is not surprising since they are located at similar latitudes and share many hydrographic characteristics, like input of both warm and saline Atlantic water, as well as cold and less saline Arctic water. Literature review suggests that total annual primary production is intermediate in the eastern basins and peaks in the Labrador Sea, while the Irminger Sea is the most oligotrophic sea. This was not reflected in the measurements of different trophic levels taken during the cruise. The potential new production was estimated to be higher in the Irminger Sea than in the eastern basins, and while the biomass of mesozooplankton was similar across basins, the biomass of mesopelagic micronekton was about one order of magnitude higher in the western basins, and peaked in the Irminger Sea, where literature suggests annual primary production is at its lowest. The eastern basins hold huge stocks of pelagic planktivore fish stocks like herring, mackerel and blue whiting, none of which are abundant in the western seas. As both epipelagic nekton and mesopelagic micronekton primarily feed on the mesozooplankton, there is likely competitive interactions between the epipelagic and mesopelagic, but we're currently unable to explain the estimated ~1 order of magnitude difference in micronekton standing stock. The results obtained during the survey highlight that even if some aspects of pelagic ecosystems are well understood, we currently do not understand overall pelagic energy flow in the North Atlantic.

Description: We greatly appreciate the Captain and crew of the R.V. G.O. Sars for their dedication and help during the BASIN survey. We also thank the technical support from the Institute of Marine Research that helped during the cruise and those that contributed to the processing and analysis of the data on land. The sampling, data analysis and reporting have been supported by IMR and University of Bergen through funding of ship time, laboratory costs and salaries of researchers through internally funded projects. We would also like to acknowledge the funding from Euro-BASIN, EU FP7, Grant agreement No 264933, HARMES, Research Council of Norway project number 280546 and MEESO, EU H2020 research and innovation programme, Grant Agreement No 817669. KD undertook this study as part of the Ecosystem Studies of Subarctic and Arctic Seas (ESSAS) programme.

Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Klevjer, T., Melle, W., Knutsen, T., Strand, E., Korneliussen, R., Dupont, N., Salvanes, A. G. V., & Wiebe, P. H. Micronekton biomass distribution, improved estimates across four north Atlantic basins. Deep-Sea Research Part II: Topical Studies in Oceanography, 180, (2020): 104691, doi:10.1016/j.dsr2.2019.104691.

Description: Distribution of micronekton was investigated during early summer of 2013, using data from a cruise covering the central parts of four north Atlantic basins, the Norwegian Sea (NS), Iceland Sea (ICS), Irminger Sea (IRS), and Labrador Sea (LS). Continuous underway acoustics mapped vertical and horizontal distributions, and trawl sampling provided data on biomass and taxonomic composition. The hull mounted acoustics and trawl catches suggested that, among the four basins, biomass of epipelagic, larger nektonic species (〉20 cm length) during the cruise was highest in the NS and ICS basins, while mesopelagic non-gelatinous micronekton biomass peaked in the IRS and LS basins. Biomass of Scyphozoa was also about 1 order of magnitude higher in IRS and LS compared to ICS and NS. In ICS and NS, crustaceans made up about 50% of total non-gelatinous micronekton biomass, with fish making up less than 20% of total biomass. In contrast, fish constituted more than 60% of non-gelatinous biomass of catches in IRS and LS. In catches from ICS and NS the myctophid Benthosema glaciale dominated the catches, whereas bathylagids, gonostomatids, barracudinas and stomiids contributed to the high biomass densities of fish in IRS and LS. In addition to the differences in biomass between the basins, the acoustic measurements suggested gradients within the north-eastern basins, and large differences in vertical distribution of biomass between the basins during the cruise.

Description: The detailed comments of two anonymous reviewers improved this paper. We gratefully acknowledge the cooperative effort and support provided by the Captains and Crew of the RV G.O. Sars during the six-week trans-Atlantic expedition. We are sincerely thankful for the financial support of the Institute of Marine Research that made the mission with G.O. Sars possible. The EU is thanked for support through EuroBasin (Integrated Project on Basin Scale Analysis, Synthesis and Integration), funded by Framework Programme 7, Contract 264933. The Research Council of Norway is thanked for the financial support through “Harvesting marine cold-water plankton species - abundance estimation and stock assessment” - (Harvest II, RCN 203871). The work is also a contribution to the Norwegian Sea Ecosystem Programme at IMR.