All Pacific (Oncorhynchus spp.) and Atlantic (Salmo spp.) salmon species are anadromous, being spawned in rivers and lakes and migrating to sea as smolts to grow to maturity, before returning to the rivers to complete the life cycle. Like all migratory species, their migration puts them at risk of entrainment and impingement at pumping stations, hydroelectric schemes and other engineering facilities.
The conventional mitigation against entrapment at water offtakes involves the use of physical screens, with mesh sizes small enough (typically 6-12.5 mm) to exclude the smallest life stages. However, fine screens impede flow and can become blocked, risking shutdown of operations, especially in nutrient rich waterways and estuarine systems. Behavioural barriers based on FGS’s acoustic SPA or BAFF technologies provide an effective and cost efficient (sometimes the only practical) solution in these cases.
Hearing sensitivity in salmonids species is restricted to lower frequencies, from infrasound (<20 Hz) to a few hundred Hz. Salmonids are also most sensitive to particle motion rather than sound pressure and this means that they will react only when close to the acoustic deterrents (within a few metres). As a result when designing a system it is necessary to ensure the water velocities at the offtake are low enough for them to swim away. This applies to BAFF and SPA technologies.
Salmonids also react strongly to strobe lights and FGS High Intensity Lights offer an alternative option for salmonids deflection. Highest deflection efficiencies can be achieved when acoustic and strobe stimuli are combined, in FGS SILAS™ technology.
FGS have many successful installations of BAFF, SPA and SILAS™ systems used for protection of salmonids smolt migrations in UK, Europe and North America and would be pleased to provide further details.