Quantifying behaviour of migratory fish: Application of signal detection theory to fisheries engineering

Abstract

Behavioural devices that attract or deflect migrating fish to preferred routes are used to enhance the efficiency of mechanical structures (e.g. screens at turbine and other intakes) or as an alternative to them when their application is deemed unviable. Fish response to stimuli (signals) encountered, and consequently the efficiency of these behavioural devices, can be highly variable. To further develop efficient behavioural screens and fish pass technology there is a need for a generic framework to (1) better understand fish response to environmental stimuli and causes of variation, and (2) quantify ability to detect stimuli and respond in a way deemed appropriate from a management perspective. This paper considers application of signal detection theory (SDT) to fish passage research, using downstream migrating juvenile salmonids as a model. Support is provided in the scientific literature for two key assumptions, that downstream migrants are able to exhibit volitional behaviour in response to stimuli encountered and that these behaviours can be interpreted by an observer to indicate the detection of a signal. Re-evaluation of available data highlights the temporal variability of decision making and elicitation of behaviour within and between individuals, and that sensitivity (d′), a measure of the ability to detect a signal (e.g. hydraulic gradient), increases with signal strength and when multimodal stimuli are presented. SDT is likely to provide a useful “first base” for understanding and quantifying fish behaviour in the development of screens and fish passes.