NWAFC processed report ; 83-05

Fish are attracted to baits mainly by olfactory stimuli (smell). Past studies show that most olfactory attracted fish swim against the current, and that currents near the bottom distribute the smell from the baits. The emission of attractive olfactory stimulants from the bait decreases rapidly with time so that within an hour about 40% of the total soluable proteins (which are main stimulants) may have dissipated. The Interactions between changing leaching rate of smell, current speed and direction in relation to the line, and mixing of the smell fields from adjacent baits is expected to be relatively complex. A numerical model has been designed to study these interactions. The formulas used in the model are described, and the model is reproduced, in the Appendix. The model was used to compute smell pattern developments with time with different current speeds and directions in relation to the line of baits. Hook (bait) spacing influences the strength of the smell field as does the direction of current in relation to the line of baits. The smell field in a rotary current is greatly determined by the current direction at the time of the setting of the long line. To validate the computed distributions of smell, current measurements at very close intervals near the bottom are required (5, 10, 20, and 40 cm from the bottom). Furthermore there Is a need to know the lowest smell concentrations at which fish react In various conditions and commence the search for bait (attraction threshold)

National Marine Fisheries Service (NMFS)