FEEDING ECOLOGY AND DAILY RATION OF THE PELAGIC ARMORHEAD, PSEUDOPENTACEROS-WHEELERI AT SOUTHEAST HANCOCK SEAMOUNT

The unusual life history of pelagic armorhead, Pseudopentaceros wheele ri, includes occupation of epipelagic subarctic and transitional water s of the northeast Pacific Ocean and Gulf of Alaska as subadults and s ubsequent recruitment to the southern Emperor and northern Hawaiian Ri dge (SE-NHR) seamounts in the central North Pacific Ocean where they a ssume a demersal existence and begin maturation as adults. Feeding eco logy and daily ration were examined in pelagic armorhead during field studies conducted at Southeast Hancock Seamont (29 degrees 48' N, 179 degrees 04' E) in the SE-NHR seamounts. A total of 1133 stomachs colle cted during June-July 1985, January 1988, and July 1988 were examined for contents; only 19.7% contained food items. The diet consisted of p elagic tunicates and other micronektonic animals that are associated w ith the vertically migrating sonic scattering layer that is advected o ver the seamount from the adjacent oceanic environment. Peak feeding o ccurred in the early morning on migrating organisms likely frapped by the expanse of the seamount summit during the morning descent. Newly r ecruited armorhead had lower feeding rates than older, previously recr uited fish. Estimates of daily ration for previously recruited armorhe ad were 1.17 g (0.26% of body weight) in the summer of 1985 and 12.87 g (2.86% of body weight) in the summer of 1988. Since estimated values for the evacuation coefficient and the duration of the daily feeding period did not differ between sampling periods, the increase in daily ration was due to an increase in feeding rate. The proportion of the d iet composed of pelagic tunicates was also higher in 1988.