Kirsteen MacKenzie

Christian Lydersen

Tore Haug

Heli Routti

Jon Aars

Clare Andvik

Katrine Borgå

Aaron Fisk

Sonnich Meier

Martin Biuw

Andrew Lowther

Ulf Lindstrøm

Kit M. Kovacs

Sampling

Samples of skin and blubber were taken from blue, fin, humpback and sperm whales, using a custom-built biopsy dart launched from either an airgun or from a crossbow (see Tartu et al. (2020) and Lydersen et al. (2020) for full details) using a small boat or a helicopter to approach the whales. Samples from white whales were taken from physically restrained animals, captured for tracking studies (Vacquié-Garcia et al. 2018). Ringed and bearded seal samples were collected from animals shot during the annual sport hunt in Svalbard (Bengtsson et al. 2020). Minke whale samples were taken during the Norwegian commercial harvest. Samples from polar bears and walruses were taken from chemically immobilised individuals, according to the methods described in Scotter et al. (2019) and Tartu et al. (2016a). Sampling was approved, where relevant, by the National Animal Research Authority, the Norwegian Animal Care Authority and the Governor of Svalbard (Villanger et al. 2011; Tartu et al. 2016a for details, see 2020; Scotter et al. 2019).

Stable isotope analyses

Stable isotope compositions of carbon and nitrogen were analysed in 152 skin samples (21 blue, 27 fin, 6 humpback, 17 minke, 5 sperm and 10 white whale samples, 5 bearded and 12 ringed seal samples, 37 walrus samples, and 12 polar bear samples, see Table 1 for sampling by years). We freeze-dried these samples for 48 hours at -48°C before homogenisation. We removed lipids using a 2:1 chloroform-methanol solvent extraction, then thoroughly washed samples in deionised water, before drying and weighing into tin capsules for analysis. Isotope compositions were measured using a Delta V Advantage Thermoscientific Continuous Flow Mass Spectrometer (Thermo Scientific, Bremen, Germany) coupled to a 4010 Elemental Combustion System (Costech Instruments, Valencia, CA, USA), with analytical precision of 0.2 ‰ for both d15N and d13C, as measured in NIST 1577c, tilapia muscle, USGS 40 and Urea standards.

Fatty acid analyses

We analysed fatty acid compositions from 349 frozen blubber (12 blue, 5 fin, 3 humpback, 200 minke and 15 white whale samples, and 31 walrus samples) and subcutaneous fat samples (83 polar bear samples). Samples were methylated, and fatty acid methyl esters analysed by gas liquid chromatography, according to the methods in Meier et al. (2016) for minke whales and Tartu et al. (2016a) for other samples.

We screened all FA data from blue, fin, humpback, and white whales, polar bears and walruses to remove FAs that were not measured in all species, along with any in-vivo altered FAs, leaving only dietary source FAs, and then to remove FAs comprising < 1 % of dietary FA compositions by mass in all samples (Mayzaud and Ackman 1978; Iverson et al. 2004; Falk-Petersen et al. 2004; Linder et al. 2010; Parrish 2013; Chavarie et al. 2016, 2020; Kohlbach et al. 2018). We then renormalized data on the compositions of the remaining 23 dietary FAs to 100 % within each animal to facilitate comparisons.

Data: All walrus, and some blue (n=18) and fin (n=12) whale SI data have been published previously (Routti et al. 2019; Scotter et al. 2019; Tartu et al. 2020), as have FAs data from minke whales (Meier et al. 2016) and polar bears (Tartu et al. 2016b; a).

CEOS IDN DIF

9.8.4