Normally treated as polytypic, but evidence incomplete and further examination required; subspecific status of populations breeding in Severnaya Zemlya, New Siberian Is and Bering Sea uncertain. There are significant size differences between races, but no genetic differences at either mitochondrial DNA or at microsatellite loci#R. Two subspecies recognized.
Winters mainly in low Arctic waters from Grand Banks of Newfoundland E across N Atlantic to N Norway; also regularly in boreal zone S over Scotian Shelf and Gulf of Maine E to N Scotland and North Sea, rarely farther S.
Food and feeding
Status and conservation
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