Dataset for paper "Niches of marine mammals in the European Arctic" in Ecological Indicators. Data include carbon and nitrogen stable isotope compositions for blue whales, fin whales, humpback whales, minke whales, white whales, walruses, bearded seals, ringed seals and polar bears, and dietary fatty acids compositions for blue whales, fin whales, humpback whales, minke whales, white whales, walruses and polar bears.

Zooplankton dataset over the Kongsfjorden to Fram Strait marine biological transect collected in connection with Environmental monitoring of Svalbard and Jan Mayen (http://www.mosj.no/en/) programme. The dataset covers summers 1996-2016 except for 1998 when summer samples were not taken. The dataset contains only zooplankton collected with the MultiNet plankton sampler. The results published in Hop et al. 2019 (see the "Citation Custom" field) are based on this exact dataset. Norwegian Polar Institute"s database will contain extended data based on this dataset, and any users post-2019 are encouraged to use the extended dataset instead. The dataset is compiled in three files: **kf_zooplankton_abundance_data** contains zooplankton abundance data in *individuals per cubic meter*. The columns of the dataset consists of species and stage codes specified in the species metadata, while the rows consist of samples indicate in the sample metadata **kf_zooplankton_sampling_meta** contains row metadata for zooplankton abundance. Columns: id = row name in zooplankton abundance data; expedition = expedition/cruise name; station = standard station name across the MOSJ transect; sample_name = internal sample name for backwards compatibility; region = region category used in Hop et al. 2019; longitude = longitude as decimal degrees (WGS84); latitude = latitude as decimal degrees (WGS84); date = date in yyyy-mm-dd format; from = depth in meters where the MultiNet opened ; to = depth in meters where the MultiNet closed; comment = specific comments concerning the sample. **kf_zooplankton_species_meta** contains column metadata for zooplankton abundance. Columns: id = column name in zooplankton abundance data; species = scientific taxa name; stage = life stage; length = length group; origin = the assumed origin of species (Atlantic, Arctic, Both or Unknown); taxa = used for grouping of species data based on taxonomy in Hop et al. 2019; biomass_conv = abundance to biomass conversion factor, see Hop et al. 2019.