Sex differences in diving and foraging behaviour of northern elephant seals. Symp

• Main Authors: B J Le Boeuf, D E Cro Cker, S B Blackwell, P A Morris, P H Thorson
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1993
• Subjects: Gulf of Alaska; Pacific; Elephant Seals; Alaska; Aleutian Islands
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1081.4710; http://mirounga.ucsc.edu/leboeuf/pdfs/LeBoeufetal.1993.pdf

Sex differences in the foraging behaviour of adult northern elephant seals, Mirounga angustirostris, are predicted from the great disparity in size between the sexes, males being 1.5-10 times larger than females. Males must consume approximately three times more prey per day than females. By examining the diving behaviour, during which all foraging occurs, our aim was to elucidate how males do this and when the strategy develops. Dive data were collected by microcomputer time-depth recorders attached to the backs of free-ranging seals (nine adult males, 10 adult females, seven juvenile males and six juvenile females) during periods at sea ranging from one to three months. The sexes foraged in different locations and exhibited differences in foraging-type dives, suggesting different foraging strategies and, possibly, different prey. Females moved steadily across the north-eastern Pacific from the coast to as far as 150 oW, in the range 44--52 oN, foraging daily en route. Males migrated to areas along continental margins off the state of Washington, to as far as the northern Gulf of Alaska and the eastern Aleutian Islands, where they exhibited concentrated foraging. Female foraging was exclusively pelagic, with dive depth varying with diel vertical movements of prey, such as squid, in the deep scattering layer. Males exhibited two types of foraging dives, neither of which followed a diel pattern: pelagic dives like those of females, observed mainly during transit, and flat-bottomed dives (which accounted for over 40% of their dives), which occurred near continental margins. The characteristics of these dives, such as occurring in a long series to a uniform depth, and their location, suggest the pursuit of benthic prey such as skates, rays or small sharks on seamounts, guyots or the edge of the continental shelf or, alternatively, the pursuit of prey in the water column by means of a sit-and-wait strategy. The sex differences observed in adults were evident in juveniles less than 18 months old, suggesting that a ...