Hunger and light level alter response to bait by Pacific halibut: laboratory analysis of detection, location and attack

Laboratory experiments with Pacific halibut Hippoglossus stenolepis revealed that hunger level had a significant effect on the first detection of bait, the number of baits located and attacked, the time required to locate and attack baits and handling times. In all cases, feeding motivation and efficiency increased with hunger. Light level influenced general locomotory activity and location and attacks on baits, but not detection or handling times. The effect of light was interactive with fish hunger level. Hungry fish could locate and consume baits in all light levels, ranging from daylight conditions to near darkness (10⁻⁸ µmoles photons m⁻² s⁻¹), but location, attack and handling times were all significantly elevated in low light conditions, and attack rates were significantly reduced. In the dark, only 50% of the baits were located and only 17% were attacked. Performance metrics were relatively similar among three higher light treatments (10⁻⁵, 10⁻³ and 10⁻¹ µmoles photons m⁻² s⁻¹) where bait location and attack were more efficient. Active space and effective area associated with baited fishing gear will vary because hunger and light levels affect variation in bait detection, locomotion and feeding behaviour. Consequently, fishing activity and stock assessments that depend upon bait may be compromised by spatial and temporal variation in prey abundance, time of day, season, depth and other environmental variables that influence feeding motivation and efficiency.