The predictable narwhal: satellite tracking shows behavioural similarities between isolated subpopulations

Abstract

Listen

Translate article

AbstractComparison 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 ofGreenland 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 theScoresbySound 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 inScoresbySound inSeptember and arrived at the edge of the continental shelf byNovember. Here, they stayed throughMay–June and conducted daily dives to the mesopelagic zone at ∼1000 m depth. Despite the isolation by the landmass ofGreenland 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 forGreenland 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 otherArctic cetaceans and renders narwhals more vulnerable to large‐scale changes in their restricted and specialized habitats.