SummaryThe bowhead whale (Balaena mysticetus) is estimated to live over 200 years and is possibly the longest-living mammal. These animals should possess protective molecular adaptations relevant to age-related diseases, particularly cancer. Here, we report the sequencing and comparative analysis of the bowhead whale genome and two transcriptomes from different populations. Our analysis identifies genes under positive selection and bowhead-specific mutations in genes linked to cancer and aging. In addition, we identify gene gain and loss involving genes associated with DNA repair, cell-cycle regulation, cancer, and aging. Our results expand our understanding of the evolution of mammalian longevity and suggest possible players involved in adaptive genetic changes conferring cancer resistance. We also found potentially relevant changes in genes related to additional processes, including thermoregulation, sensory perception, dietary adaptations, and immune response. Our data are made available online (http://www.bowhead-whale.org) to facilitate research in this long-lived species.

Comparison of behavioural similarities between subpopulations of species that have been isolated for a long time is important for understanding the general ecology of species that are under pressure from large‐scale changes in habitats. Narwhals (Monodon monoceros) east and west of Greenland are examples of separated populations that, in different ocean parts, will be coping with similar anthropogenic and climate‐driven habitat alterations. To study this, 28 narwhals from the Scoresby Sound fjord system were tracked by satellite in 2010–2013. The average duration of contact with the whales was 124 days with one tag lasting 305 days and one whale recaptured <1 km from its tagging site 366 days later. All whales exhibited the same migratory pattern. The whales departed from the summering grounds in Scoresby Sound in September and arrived at the edge of the continental shelf by November. Here, they stayed through May–June and conducted daily dives to the mesopelagic zone at ∼1000 m depth. Despite the isolation by the landmass of Greenland and the genetic differentiation from other narwhal populations, there is still a remarkable similarity not just in behavioural traits like phenology of migrations and movements in relation to sea ice formation, but also in site fidelity, diving behaviour, feeding ecology, habitat selection, daily travel speed and even potential conflicts with fisheries for Greenland halibut (Reinhardtius hippoglossoides). Greenland halibut are likely target prey during the deep dives in winter but capelin (Mallotus villosus) may, with ocean warming, become of increasing importance. The ocean‐wide predictability in culturally inherited migration patterns, size of wintering grounds and habitat selection among narwhal populations is certainly different from other Arctic cetaceans and renders narwhals more vulnerable to large‐scale changes in their restricted and specialized habitats.

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The North Water polynya (*76°N to 79°N and 70°W to 80°W) is known to be an important habitat for several species of marine mammals and sea birds. For millennia, it has provided the basis for subsistence hunting and human presence in the northernmost part of Baffin Bay. The abundance of air-breathing top predators also represents a potential source of nutrient cycling that maintains primary production. In this study, aerial surveys conducted in 2009 and 2010 were used for the first time to map the distribution and estimate the abundance of top predators during spring in the North Water. Belugas (Delphinapterus leucas) were not detected north of 77°20 0 N but were found along the coast of West Greenland and offshore in the middle of the North Water with an abundance estimated at 2245 (95 % CI 1811-2783). Narwhals (Monodon monoceros) were widely distributed on the eastern side of the North Water with an estimate of abundance of 7726 (3761-15 870). Walruses (Odobenus rosmarus) were found across the North Water over both shallow and deep ([500 m) water with an estimated abundance of 1499 (1077-2087). Bearded (Erignathus barbatus) and ringed seals (Phoca hispida) used the large floes of ice in the southeastern part of the North Water for hauling out. Most polar bears (Ursus maritimus) were detected in the southern part of the polynya. The abundances of bearded and ringed seals were 6016 (3322-10 893) and 9529 (5460-16 632), respectively, and that of polar bears was 60 (12-292). Three sea bird species were distributed along the Greenland coast (eiders, Somateria spp.), in leads and cracks close to the Greenland coast (little auks, Alle alle) or widely in open water (thick-billed guillemots, Uria lomvia).

The effects of climate change on marine ecosystems and in particular on marine top predators are difficult to assess due to, among other things, spatial variability, and lack of clear delineation of marine habitats. The banks of West Greenland are located in a climate sensitive area and are likely to elicit pronounced responses to oceanographic changes in the North Atlantic. The recent increase in sea temperatures on the banks of West Greenland has had cascading effects on sea ice coverage, residency of top predators, and abundance of important prey species like Atlantic cod (Gadus morhua). Here, we report on the response of one of the top predators in West Greenland; the harbour porpoise (Phocoena phocoena). The porpoises depend on locating high densities of prey species with high nutritive value and they have apparently responded to the general warming on the banks of West Greenland by longer residence times, increased consumption of Atlantic cod resulting in improved body condition in the form of larger fat deposits in blubber, compared to the situation during a cold period in the 1990s. This is one of the few examples of a measurable effect of climate change on a marine mammal population.