Sensory, behavioural barriers (electricity, light, sound, air-water curtains)

Introduction

Fish are deterred by a series of measures, including flashing lights, noise, air bubbles and electrical power. This can be used to control fish from dangerous migration routes, such as intake for turbines. The measure initially only works if the fish has alternative migration routes, for example escape routes and safe bypasses. The guiding impact can be improved with attraction measures such as increased water flow to a bypass (repulse and attract). Common for repulsion measures is that they usually only work for parts of migrating fish, that they work less well by flooding and are selective in terms of species and sizes. Fish may also be accustomed to deterrence measures over time, so that they get lower efficiency.

Design varies between the methods and refers to the literature below. The most important deterrence methods are:

• Electric screens
• Strobe light
• Bubble curtains
• Acoustic deterrence, e.g. BAFF (bio-acoustic fish fence), which is a perforated tube located below the surface that emits sound and compressed air, which will act as a repellent on fish.

Promising results have been obtained with various experimental behavioural screens in laboratories or on test sites. However, not many prototype installations have been evaluated. Furthermore, the technology has not met the expectations and the results obtained in field applications have been much less reliable than those obtained under controlled conditions (EPRI, 1986) (Kynard, et al., 1990), (EPRI, 1994), (Gosset, et al., 1999), (Therrien, et al., 1998) (Travade, et al., 1999), (Larinier, et al., 2002), (Bau, et al., 2008). Furthermore, their scope of application is otherwise limited to low flow velocities (<0.3 m/s).

Care should be taken when using behavioural barriers, especially since manufacturers of these products have a high marketing interest to promote the use of their technology and may deliberately overestimate their effectiveness (Larinier, et al., 2002).

Methods, tools, and devices

During planning

Sensory and behavioural barriers like electricity, light, sound and air/water curtains are not efficient used alone and only works for specific species. Correctly choosing and designing the combined mitigation measure (like fine mesh screens) is imperative.

During implementation

Attraction and repulsion measures are installed in collaboration between fish migration experts and product suppliers.

During operation

Such barriers are convenient for designers and users alike because, unlike physical barriers, they require only minimum maintenance and cleaning efforts against blockage.

Assessment of efficiencies can be obtained by survey of fish by telemetry.