The seals employ a grab and swallow technique of feeding, taking such prey as hake, dogfish, rays, octopus and crabs, generally from the ocean bottom. The danger from orcas is greater here than in mid-ocean depths, but the quantity and quality of food allow the adult males to gain the weight they need to survive their fasts in the rookery and the roughly five months a year travel time between the rookery and feeding ground. Their two foraging trips are approximately equal in length at four months for older males and five months for juveniles.

The female seals do not grow as large as the adult males. Females spend two more months at sea each year than males do.  They forage primarily in deep mid-ocean water, typically feeding at depths well above the bottom. Their vast foraging area is indicated in the red spots on the map below. Recent evidence shows that their diet is primarily lantern-fish, hake and ragfish, with less than 10% squid.

Even during the day it is very dark in the deep water where they hunt for food. Their eyes are particularly sensitive to the bioluminescent colors of prey, such as lanternfish and squid, at their foraging depths.

Unlike the males, the two foraging trips of adult females are of quite different lengths – approximately 2.5 months between weaning their pup and returning to molt and 7.5 months between the end of the molt and birthing. During this longer second period, the female is nourishing her baby as well as herself. Evidence suggests that their daily food intake may average 20 kg (44 lbs.) and be as much as 32 kg (70 lbs.) per day. Weight gains of 1 kg (2.2 lbs.) per day at sea are typical for pregnant females.