[2] Pelagic cormorants have relatively short wings due to their need for economical movement underwater, and consequently have the highest flight costs of any bird.

[5] This is a smallish cormorant which measures 25 to 35 in (64 to 89 cm) in length, with a wingspan of about 3.3 ft (1.0 m) and a weight of 52–86 oz (1,500–2,400 g) when fully grown.

The long thin bill and the large feet with all-webbed toes are black throughout the year, while the patch of dark naked skin below the eye turns a vivid magenta in the breeding season.

Other North Pacific cormorants and shags are larger, with a thicker bill, and/or lack the white thighs in breeding plumage.

It furthermore is found on the Aleutian and other Bering Strait islands, and from the Russian Far East Chukchi Peninsula via Sakhalin south to Kamchatka, and ultimately Kyūshū (though not the rest of Japan).

Typical prey are smallish, bottom-living non-schooling fishes, such as Ammodytes sand eels, sculpins (Cottidae), gunnels (Pholidae) and Sebastes (rockfish).

It has been observed to join mixed-species feeding flocks going after schools of young Pacific herrings (Clupea pallasii).

Thus, the birds return to a safe place after foraging to preen and dry their feathers, typically adopting a spread-winged posture.

Local populations may be all but wiped out temporarily by oil spills, and on a larger scale competition with gillnet fisheries and drowning in such nets is putting a limit to its stocks.

Modern authors were previously reserved about uniting all cormorants in one "wastebin genus", but most revisions published had on phylogenetic merit.

Similarly, Leucocarbo would refer to the group around the imperial shag (P. atriceps) complex, which occurs on the opposite end of the Earth from P. pelagicus.

Apart from looking almost alike, these two species also "yawn" many times in a row instead of giving the display just once, twist their bodies before taking flight during courtship, and the male and female post-landing calls are identical.

It was described from the bones of three individuals snared in fishing nets in the late 1950s at Constantine Harbor on Amchitka in the Aleutian Islands.

The specific name kenyoni honors USFWS biologist Karl W. Kenyon, who collected the type specimen USNM 431164 on 22 February 1959.

As distinctive cormorants were never seen alive in recent years on Amchitka, it was conjectured by some that Kenyon's shag might have gone extinct in the 1960s–1970s (marine pollution and overfishing would be possible reasons).

[18] However, a subsequent analysis of a larger number of comparison specimens of the pelagic cormorant – mainly from birds that fell victim to the Exxon Valdez oil spill – determined that the bones were attributable to small females of the latter species, and that their apparent distinctness was due to the original canonical analysis being distorted by insufficient specimens.

Verification of subspecies status would require DNA sequence analyses however, since the differences in morphology are not large and there is much variation between individuals.

[19] In 2003, during an USFWS survey three small pelagic cormorants whose bills appeared to be red were noted at Karab Cove on Agattu Island.

The large birds from the Prince William Sound region were formerly called U. p. robustus, but are not considered distinct today.