Ichthyoplankton vertical distribution and vertical migration in Auke Bay, Alaska

Abstract

Vertical distributions of larval fishes were examined in Auke Bay, Alaska using an opening/closing 1.0 m² Tucker trawl horizontally towed, at six depths, every four hours for 24 hours. In daytime, larval fishes concentrated at 5-10 m depths, coincident with highest prey densities. At night, osmerids ascended to the surface, walleye pollock and northern smoothtongue descended, whereas other species simply dispersed. A significant relationship existed between larval walleye pollock length and depth distribution with larger larvae migrating further than smaller larvae. Yolk-sac larvae were randomly distributed vertically. Larval walleye pollock are daytime feeders, primarily on copepod nauplii. Larval pollock approximately 7.0 - 7.5 mm standard length expand their diet to include copepodites.