Mythbusters: Using science to debunk misconceptions about Acoustic Fish Deterrent noise, and its effect on Marine Mammals.
In the wake of growing concerns and widespread misinformation regarding the impact of Acoustic Fish Deterrent (AFD) systems on marine mammals and beachgoers, it is crucial to set the record straight.
Despite claims propagated by certain groups, comprehensive research and empirical evidence shows that AFD systems pose minimal threat to the auditory well-being of marine mammals, including seals, dolphins, and whales, nor can they be heard on the beaches of the Severn Estuary.
This article aims to rebut the misconceptions and present an educated view based on extensive research.
Understanding AFD Systems and Marine Mammals
AFD systems emit low-frequency signals to deflect fish from certain areas, such as the intakes of power stations. These systems typically operate at frequencies less than 1000Hz. In contrast, marine mammals, including seals and cetaceans like porpoise, dolphins and whales, communicate and perceive sounds primarily in the high-frequency range in the tens of thousands of Hertz (kHz). Grey seals’ peak hearing is around 20kHz, while harbour porpoise peak hearing is in the region of 125kHz. This fundamental difference in frequency ranges is crucial in understanding the negligible impact of AFD systems on marine mammals.
Frequency Overlap: A Minimal Concern
While it is acknowledged that some cetaceans can hear low-frequency sounds, the overlap with the frequencies used by AFD systems is minimal. This distinction is significant because it shows that the sound signal from an AFD system is outside the optimal hearing range of these marine mammals, reducing the potential for disturbance or harm.
Empirical Evidence: The Hartlepool Study
One of the most telling pieces of evidence comes from an early evaluation of an AFD system at the Hartlepool power station, located near a grey seal colony. This study, conducted nearly 30 years ago, was specifically designed to monitor any potential impact on the seal colony. The findings were unequivocal: there was no discernible impact on the colony, underscoring the benign nature of AFD systems regarding marine mammal life.
Debunking the “Jumbo Jet” Myth
Another piece of misinformation is the comparison of the noise generated by AFD systems to that of a jumbo jet. Such claims are not only unfounded but also misleading.
Extensive modelling into the sound levels produced by AFD systems demonstrates that while the source level can be 160dB re 1µPa, this is an underwater sound level, which is measured on a different scale to sound in air (dB). In a boat directly above the intake the AFD would sound like a vacuum cleaner. Very different to a jet engine.
An additional factor is that the AFD is installed two miles off-shore, and so the sound on the beach is less than a whisper in a library, and well below surround sound levels – effectively making it silent.
This comparison serves to highlight the relatively low acoustic impact of AFD systems, further supporting the argument against their purported threat to marine mammals, or people on the shore.
Dr David Lambert states, “if the systems did deflect seals and porpoises, then the company would be marketing the systems to deflect seals from fish farms and other areas that need protecting, which it doesn’t, and is the reason why the company is called Fish Guidance Systems, and not Seal Guidance Systems.”
The debate surrounding the environmental impact of Acoustic Fish Deterrent (AFD) systems, particularly in relation to Hinkley Point C’s operations, has stirred considerable public concern. Misinformation has led to fears that the sound from these systems could disrupt the tranquillity of nearby shorelines. However, a closer examination of the science behind AFD technology, along with expert analysis, reveals a different truth: the fear that the AFD will be heard from shore is unfounded.
