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 data submitted is used in a comparative analysis of the diet of one of the globally most numerous myctophids, the Glacier lantern fish Benthosema glaciale, across four deep basins of the North-Atlantic. B. glaciale is a small fish species that contribute to carbon flux to the deep basins of the open ocean, and is thus considered an important element of the biological carbon pump (BCP). Data submitted is length and weight of fish analyzed for stomach content. In addition there are available taxonomic information, weight and number of prey items of each fish that has stomach content, as long as it has been possible to assign prey to a species or other taxonomic category. Unidentified prey usually had a high degree of digestion and individual items could not be counted, but could be weighed. Sampling were undertaken onboard the RV G.O. Sars during a six week long transatlantic scientific survey from Bergen (Norway) to Nuuk (Greenland) and back to Bergen in May and June 2013. Samples of B. glaciale for stomach content analysis were collected from three Harstad trawl hauls and 16 Macroplankton trawl hauls. The Harstad trawl is a graded (variable mesh size), small mid-water trawl with 20 m vertical opening and 15 m wing spread (Godø et al., 1993). The Macroplankton trawl on the other hand is a light pelagic trawl that has a nominal 6x6 m trawl opening and mesh size of 3 mm square light opening (8 mm stretched, knot to knot) from the trawl mouth along the entire trawl length to the cod-end (Hassel et al., 2017; Klevjer et al., 2020).