Seals of approval


Predator control technology and best practice has evolved to meet MMPA restrictions

Animal welfare conversations usually focus on interactions between fish and people but managing conflicts between fish and marine mammal predators is also important for maintaining high welfare standards on a fish farm. Attacks from predators like seals can cause high levels of fish stress and mortalities if the right precautions are not taken.

Approaches to protecting fish from predators have evolved over the years and upcoming regulatory changes have prompted farms to further refine their technology and processes to ensure protecting their fish doesn’t negatively impact local marine life.

What’s changing?

When new import provisions of the Marine Mammal Protection Act (MMPA) come into play on 1 January 2022, the USA will ban fish product imports from countries whose farming operations cause ‘mortality and serious injury of marine mammals’. With Scottish salmon exports to the USA currently worth £179 million a year – Scotland’s largest non-EU export market – preparations for the MMPA are high on the industry’s agenda.

It’s important to understand the MMPA is not a ban on acoustic devices or any particular technology; the focus is on reducing mortalities and serious injury. One thing that will be impacted though is a last resort option that currently allows farms to apply for a license to shoot seals.

An industry wide drive to reduce seal mortalities has already led to large reductions in the number of seals being shot, but to be MMPA compliant this will no longer be an option in future. Farms have known about this change for several years and have been improving their technology and processes in preparation.


Farmers hoped for a single solution

In the early days of addressing predation problems farms hoped to find a perfect single solution. The two most common approaches adopted were acoustic deterrents and reinforced anti-predator nets.


Early acoustic deterrents didn’t meet modern welfare expectations

Many farms first looked to traditional acoustic deterrent devices; systems producing noise at a single narrow frequency (10.3kHz). These offered initial success but research demonstrated habituation to these narrow frequencies after 6-12 months and some studies indicated impact on cetacean species.


Reinforced netting helped but had limitations

Another early solution some farms experimented with was anti-predator netting. These reinforced nets around the pen nets create a barrier preventing seals from making quick damaging strikes against the fish pens. Although effective at reducing fish mortalities due to seal attacks, this solution also had its limitations when used in isolation.
Seals circling the outer nets can still stress fish – putting them off their feed and slowing growth rates – and when stressed fish eventually fall to the bottom from exhaustion seals can eat them through the net.


New acoustic devices can be safe for seals and cetaceans

Innovations in acoustic technology have now allowed farms to take a more comprehensive approach blending acoustic and netting solutions for maximum protection.

Acoustic technology has come such a long way over the last few years that Ace Aquatec won the 2018 Queen’s Award for Innovation for our success in reducing conflict between seals and farms. Our US3 and RT1 acoustic deterrents were recognised for providing a step forward in both welfare and effectiveness.

The US3 is a mid-frequency deterrent designed with a wide frequency range (10-20kHz) and randomised computer-generated sound patterns designed specifically to avoid the hearing risks and habituation effects experienced by single frequency systems. The low frequency (1-2kHz) RT1 system was then developed to provide an option that avoids the sensitive hearing range of cetacean species like porpoises and dolphins; making it safe for use in areas known to have cetaceans.

Since then the company has further refined its systems to help farms prepare for potential MMPA restrictions. A thermal camera can now automatically trigger their deterrents when a seal is approaching; meaning the system only activates when needed. And a new software update adds an automatic ramp down period after every activation and synchronises every deterrent at a site to cut down the acoustic Duty Cycle.

Ace Aquatec also engage with industry groups like Freedom Foods and Scottish National Heritage to keep their technology up to date with the latest animal welfare guidance.


The future is a combination of safe acoustics, reinforced nets, and good farming practices

For the best protection against predators modern farms are now pairing a combination of anti-predator nets and acoustic deterrents with constant attention to detail on their anti-predation farming practices.

The most successful farms the company works with keep these principles in mind when focusing on reducing conflict with predators:

1. Quickly remove any dead fish to avoid attracting predators
2. Deploy acoustic deterrents before stocking the site to avoid seals getting accustomed to uninterrupted predatory behaviour
3. Keep anti-predator nets tight to minimise seal contact with fish
4. Use low frequency acoustic options (1-2kHz) if operating near cetaceans
5. Avoid acoustic deterrents using a narrow sound frequency or single tone

Change always has the potential to be scary but it doesn’t need to be. With the right blend of processes and technology in place fish farms and marine mammals can both thrive within the new MMPA regulatory framework.

For further information about Ace Aquatec please visit


Featured image: Seals can cause significant mortality and serious stress to fish.

  1. Ace Aquatec’s low frequency RT1 deterrent;
  2. Thermal image of seals from Ace Aquatec’s triggering system;
  3. Ace Aquatec’s thermal camera can detect seals then trigger deterrents;
  4. Acoustic predator deterrents on a fish farm site;
  5. Acoustic predator deterrents on a fish farm site;
  6. Aerial photo of an Scottish salmon farm using acoustic deterrents.


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