Basic modelling of fish behaviour in a towed trawl based on chaos in decision-making

A fish behaviour model using a psycho-hydraulic wheel activated by the stimuli of the fishing gear is established. It uses Lorenz chaos equations, which in effect, take the place of the brain of the fish in decision-making and generate the components of realistic fish movements. Parameters are calculated from the normalized intensity of the stimuli of the fishing gear components or neighbouring fish and these are then related to the normalized sensitivity and movement abilities of fish in order to determine the magnitude and direction of the next movement step. The step decisions made by the chaos equations result in more realistic behaviour of simulated fish. This paper develops the modelling of the fish behaviour within the fishing gear from established interpretations of observed behaviours and is linked to other relevant models of visual stimulus, flow stimulus, swimming ability, etc. The variations of swimming speed and angular velocity of fish movements derived from the simulation results fitted very well to fish behaviour recorded in field observations. The results of this developing model indicate that practical applications might extend to other towed gears, gear design, predicting selectivity, fisheries management, etc.