BEHAVIORAL-RESPONSES OF SABLEFISH, ANOPLOPOMA-FIMBRIA, TO BAIT ODOR

A behavioural bioassay was used to determine the response threshold to squid extract of sablefish, Anoplopoma fimbria, held at three differe nt feeding regimens. Sablefish responded to the odour of bait by chang ing swimming activity and turning behaviour. The response threshold to bait odour was influenced by both the amount of food eaten and the du ration of food deprivation. The total concentration of amino acids in the bait extract was assumed to determine the response threshold as ch emical fractionation studies have shown that this class of compounds i s essential for the stimulatory capacities of food extracts. When fed to satiation (9.4% wet body weight) and tested after one day of food d eprivation, the mean response threshold to total dissolved free amino acids was 4.4 x 10(-8) M (range = 7.6 x 10(-8) to 3.6 x 10(-8) M). Whe n fed at 1.6-2.3% wet body weight, the threshold sensitivity had incre ased to a mean value of 1.8 x 10(-10) M (range = 8.4 x 10(-10) to 7.0 x 10(-11) M) after one day of food deprivation; after four days of dep rivation, the sensitivity had increased oven further to a mean value o f 1.4 x 10(-11) M (range = 1.6 x 10(-10) to 1.4 x 10(-12) M). It was a lso apparent that the intensity of behavioural responses to the bait o dour increased with both stimulus concentration and duration of food d eprivation. These results suggest that sablefish intensify their searc h for prey under increased feeding motivation. The active space of a b ait source was estimated from the threshold values obtained. Depending on state of food deprivation, rate of chemical release from the bait and the current velocity, maximum lengths of active space within which sablefish would exhibit food searching responses vary from 10 m to se veral km. Stock assessment based on catch data from baited gear will n eed techniques that take into account those factors influencing active space for food searching.