Temperature affects activity and feeding motivation in Pacific halibut: Implications for bait-dependent fishing

Laboratory experiments were conducted to test the hypothesis that temperature (2-10 °C) and recent feeding history (1-14 days food deprivation) influence the activity and feeding motivation of Pacific halibut (Hippoglossus stenolepis). Activity was examined before and after presentation of a chemical cue prepared from squid (Loligo opalescens). Spontaneous activity in 2 °C was essentially zero and increased with temperature. Searching behavior increased with cue introduction in all treatments and search intensity was closely correlated with temperature. Food deprivation did not significantly affect either pre- or post-cue activity. The number of baits located, attacked and consumed increased with temperature, and the times required to accomplish those behaviors decreased significantly with temperature. In most cases, very slow responses occurred at 2 °C, differences between 4 and 6 °C were small and not significant, and times were shortest in 10 °C. Temperature did not have a significant effect on latency in attack or bait handling time, and feeding history had no significant effects on any of the timed measures. These results indicate a large potential impact of temperature on Pacific halibut catchability in longline surveys. Stock size could be significantly underestimated in a cold season or cold year and in deep water environments where temperatures are low.