ABSTRACT: Walleye pollock and sablefish, as 0+ yr juveniles, are pelagic particulate feeding planktivores. We conducted a series of laboratory experiments to determine how illumination influences prey consumption in these species, utilizing live Artemia sp. as prey. Both juvenile walleye pollock and sablefish were characterized by a sigmoidal relationship between the log of illumination and the number of prey consumed, with greater prey consumption at higher illuminations. The threshold illumination below which fish were no longer able to visually forage was approximately 5 x 10^-7 µE s^-1 m^-2 for walleye pollock and 5 x 10^-5 µE s^-1 m^-2 for sablefish, indicating that walleye pollock are better adapted for visual feeding at depth or at night than are sablefish. This is consistent with what is known about their vertical distributions at this life stage; walleye pollock make daily vertical migrations which keep them at lower illuminations than sablefish, which remain at or near the water surface throughout the diel cycle. Although feeding more effectively in the light, both species were capable of detecting and capturing prey in darkness.

KEY WORDS: Visual threshold · Nonvisual feeding behavior · Illumination · Nocturnal

Published in MEPS Vol. 181 (1999) on May 18
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1999