Foraging habitat and prey taken by least auklets at King Island, Alaska

Abstract

We examined the foraging distribution and prey use of least auklets Aethia pusilla breeding on King Island in the northern Bering Sea. The location of the King Island colony, in Alaska Coastal Water, but within auklet flight range of the oceanic Anadyr Current and the Anadyr-influenced Bering Shelf Water, provided an opportunity to identify the preferred foraging habitat of the least auklet. Least auklets fed on Neocalanus plumchrus, N. cristatus, Eucalanus bungii, and shrimp larvae, all present in Anadyr Current and in Bering Shelf Water. In early June 1984 and July 1985, auklet foraging was concentrated at and just beyond a front ca 30 km west of King Island, separating Alaska Coastal Water from Bering Shelf Water to the west; large copepods of oceanic origin occurred throughout Bering Shelf Water. Data from 1985 indicated variability in the path of the Anadyr Current; rapid changes also took place in the distribution of the least auklets'' planktonic prey. In late July 1985, we documented an intrusion of Anadyr Water from 45 km to within 25 km of King Island. Least auklets often overflew the Alaska Coastal Water and foraged in stratified Bering Shelf Water, and in Anadyr Water beyond the front. In 1986, Alaska Coastal Current Water overlaid Bering Shelf Water in much of the area to the west of King Island and a majority of auklets foraged where Bering Shelf Water was closest to the surface. Throughout the study, foraging least auklets were absent from the Alaska Coastal Current near King Island, even though alternative prey, Calanus marshallae, taken elsewhere by breeding least auklets, were present. We conclude that at King Island least auklets sought specific preferred prey in stratified water and near fronts and shifted their foraging over large distances in response to the mobile marine habitat in which their prey were abundant.