The first acoustic deterrent devices (ADDs) were developed several decades ago, and were basic, if imaginative: farmers used underwater speakers to play recordings of killer whales (orcas), a natural predator of seals. However, the latter quickly caught on and the deterrent effect was short-lived.

Modern ADDs use underwater transducers (a device that turns one form of energy into another – in this case, electrical energy into sound). The deterrent, which creates a temporary sound fence around a salmon farm, uses random frequency sweeps and tones to unsettle approaching animals or produces sound at specific frequencies and volumes to cause discomfort to an approaching seal.

Researchers and farmers have been exploring the use of different acoustic frequencies to minimise impacts on seals and other marine mammals (dolphin, whales and porpoises) in the wider vicinity, while still deterring seals from approaching too close to the salmon pens.

The Scottish salmon farming sector no longer uses acoustic deterrent devices (ADDs) that may have been considered to cause disturbance to European Protected Species.

The only circumstances in which Scottish salmon producers will use ADDs in future is where ADDs comply with both Marine Scotland and U.S. MMPA requirements and operators have been provided with evidence from suppliers of the devices’ compliance.

Further research

Salmon farmers in Scotland recognise and welcome the value of further research to refine and enhance acoustic devices that can protect farmed fish without disruption to other species, and they are working with academic institutions such as the University of St Andrews to develop the science in this area.

In parallel, farmers are working with researchers and supply chain businesses to develop and refine other deterrent technologies such as seal-proof nets, seal blinds and net tensioning systems.