Don't mind if I do: Arctic humpback whales respond to winter foraging opportunities before migration.

Migration patterns are fundamentally linked to the spatio-temporal distributions of prey. How migrating animals can respond to changes in their prey's distribution and abundance remains largely unclear. During the last decade, humpback whales (Megaptera novaeangliae) used specific winter foraging sites in fjords of northern Norway, outside of their main summer foraging season, to feed on herring that started overwintering in the area. We used photographic matching to show that whales sighted during summer in the Barents Sea foraged in northern Norway from late October to February, staying up to three months and showing high inter-annual return rates (up to 82%). The number of identified whales in northern Norway totalled 866 individuals by 2019. Genetic sexing and hormone profiling in both areas demonstrate a female bias in northern Norway and suggest higher proportions of pregnancy in northern Norway. This may indicate that the fjord-based winter feeding is important for pregnant females before migration. Our results suggest that humpback whales can respond to foraging opportunities along their migration pathways, in some cases by continuing their feeding season well into winter. This provides an important reminder to implement dynamic ecosystem management that can account for changes in the spatio-temporal distribution of migrating marine mammals.

Effects of chronic dietary petroleum exposure on reproductive development in polar cod (Boreogadus saida).

Increasing human activities in the Arctic raise the risk of petroleum pollution, thus posing an elevated risk for Arctic organisms to be chronically exposed to petroleum compounds. The endocrine disrupting properties of some of these compounds (i.e. polycyclic aromatic hydrocarbons [PAHs]) present in crude oil may have negative effects on the long and energy intensive reproductive development of polar cod (Boreogadus saida), an Arctic keystone species. In the present study, selected reproductive parameters were examined in feral polar cod exposed to crude oil via a natural diet (0.11, 0.57 and 1.14µg crude oil/g fish/day [corresponding to low, medium and high treatments, respectively]) for 31 weeks prior to spawning. Fish maturing in the current reproductive period made up 92% of the experimental population while 5% were immature and 3% were identified as resting fish. Phase I metabolism of PAHs, indicated by ethoxyresorufin-O-deethylase (EROD) activity, showed a dose-dependent increase in high and medium crude oil treatments at week 6 and 22, respectively. Decreasing EROD activity and increasing PAH bile metabolite concentrations over the experimental period may be explained by reproductive maturity stage. Significant alterations in sperm motility were observed in crude oil exposed males compared to the controls. The investigated somatic indices (gonad and hepatic), germ cell development and plasma steroid levels (estradiol-17ß [females], testosterone [males and females] and 11-ketotestosterone [males]) were not significantly altered by chronic dietary exposure to crude oil. The environmentally realistic doses polar cod were chronically exposed to in this study were likely not high enough to induce adverse effects in this ecologically important fish species. This study elucidated many baseline aspects of polar cod reproductive physiology and emphasized the influence of maturation state on biomarkers of PAH biotransformation (EROD and PAH bile metabolites).

Early life stages of an arctic keystone species (Boreogadus saida) show high sensitivity to a water-soluble fraction of crude oil.

Increasing anthropogenic activities in the Arctic represent an enhanced threat for oil pollution in a marine environment that is already at risk from climate warming. In particular, this applies to species with free-living pelagic larvae that aggregate in surface waters and under the sea ice where hydrocarbons are likely to remain for extended periods of time due to low temperatures. We exposed the positively buoyant eggs of polar cod (Boreogadus saida), an arctic keystone species, to realistic concentrations of a crude oil water-soluble fraction (WSF), mimicking exposure of eggs aggregating under the ice to oil WSF leaking from brine channels following encapsulation in ice. Total hydrocarbon and polycyclic aromatic hydrocarbon levels were in the ng/L range, with most exposure concentrations below the limits of detection throughout the experiment for all treatments. The proportion of viable, free-swimming larvae decreased significantly with dose and showed increases in the incidence and severity of spine curvature, yolk sac alterations and a reduction in spine length. These effects are expected to compromise the motility, feeding capacity, and predator avoidance during critical early life stages for this important species. Our results imply that the viability and fitness of polar cod early life stages is significantly reduced when exposed to extremely low and environmentally realistic levels of aqueous hydrocarbons, which may have important implications for arctic food web dynamics and ecosystem functioning.