DIEL VERTICAL-DISTRIBUTION OF ICHTHYOPLANKTON IN THE NORTHERN GULF OFALASKA

The diel vertical distribution patterns of several abundant ichthyopla nkton taxa were examined from depth-stratified tows off Kodiak Island in the western Gulf of Alaska during 1986 and 1987. Most larvae were f ound in the upper 45 m of the water column throughout the diel period but were concentrated in higher densities near the surface (0-15 m) in daylight hours and at greater depths at night. Four of the five domin ant taxa examined in detail showed significantly greater weighted mean depths during the night than during the day. This pattern was the opp osite to that previously reported for the numerically dominant taxa (T heragra chalcogramma) in this area. Since there was no clear relation between the diel vertical distribution of these taxa and the vertical distribution of water temperature and density or copepod nauplii prey, we hypothesize that this reverse migration is either a strategy to mi nimize spatial overlap with predators that follow a normal diel migrat ion pattern or one to optimize light levels for feeding.