by Ace Aquatec, UK


Maintaining high standards of fish welfare is a top priority for fish farmers, and for many farms operating in open waters, protecting fish from predators is an essential part of fish welfare. Often the most challenging balancing act is creating a safe environment for your fish while also minimising impact on other marine life. The Marine Mammal Protection Act (MMPA) has recently prompted renewed interest in how predator deterrent technology has evolved to be both effective and environmentally responsible.

How do predators impact fish health?

Discussions about fish welfare often focus on the interactions between fish and people, but there is also the interaction between fish and predators to consider. When predators like seals or sea lions are present at farm sites, they can cause high levels of fish stress and, also, a lot of mortalities if the right protections are not in place.

Fish mortalities from direct seal attacks are the most visible and gruesome consequence of predation but there are also other, less immediately obvious, impacts on the fish. Even with a physical barrier like anti-predator netting in place, a seal circling the pen can be stressful enough to put many fish off their feed and even cause some fish to fall to the bottom of the net out of exhaustion. And, in the case of exhaustion, these fish are then an easy target for the predating seals.

With upcoming MMPA regulatory changes, farms are looking more and more at environmental impact when assessing the methods they use to keep predators at bay.

What is changing and who is impacted?

When new import provisions of the MMPA come into play on January 1st, 2022, the USA will ban fish product imports from countries whose farming operations cause 'mortality and serious injury of marine mammals'. NOAA Fisheries, the American organisation responsible for the MMPA, defines 'serious injury' as 'an injury that is more likely than not to lead to the death of the affected marine mammal'.

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 in countries like Scotland is the last resort option, that currently allows farms to apply for a license to shoot seals.

Changing measures in Scotland

The Scottish salmon industry, with exports to the USA currently worth UK £179 million a year, is investing a lot of time investigating potential impacts of the MMPA. 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 at all in future. Farms have known about this change for several years and have been improving their technology and processes in preparation.

In the early 2000s, when farms were exploring more ethical approaches to deterring predators, many farms looked to either acoustic deterrents or reinforced netting. Technology in this area, particularly acoustic technology, has advanced a lot since those early days.

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.

Some farms tried lower dB volume devices sometimes referred to as 'pingers' that had been used in the offshore industry or on vessels to warn marine mammals they were approaching danger. These might have been suitable for keeping seals away from an offshore drilling area with no curiosities, but when installed at a fixed food source like a fish farm there was a risk of creating a Dinner Bell Effect that actually attracted seals, rather than deterring them.

Reinforced netting alone wasn't a perfect solution either

Another early solution some farms experimented with was anti-predator netting. These stronger, reinforced nets created an additional barrier between the predator and the fish; preventing seals from making quick damaging strikes against the fish pens. Although effective at reducing fish mortalities due to seal attacks, this solution had its limitations when used in isolation.

Seals could still see the fish and would circle the nets, looking for an opportunity to get at the food source. 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. And if the nets were not kept at the sufficient amount of tension, predators could still push towards the inner net and attack that way.

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 reinforced 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 success in reducing conflict between seals and farms. The US3 and RT1 acoustic deterrents were recognised for providing a step forward in both welfare and effectiveness compared to traditional acoustic devices many farms had experimented with in earlier years.

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.

Continued innovation to support MMPA preparations

Since then, Ace Aquatec has further refined these systems to help farms prepare for potential MMPA restrictions. A thermal camera can now automatically trigger 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.

All of these changes help reduce acoustic energy output into the marine environment without sacrificing the fish welfare standards that come from effective predator control. Regular engagement with industry groups like Freedom Foods, Scottish National Heritage and the Aquaculture Stewardship Council (ASC) has helped Ace Aquatec keep acoustic 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, with low impact on marine life, modern farms are now pairing a combination of reinforced anti-predator nets and acoustic deterrents with constant attention to detail on their anti-predation farming practices.

Feedback from the farms having most success in this area has been to keep the following five principles in mind when focusing on reducing conflict with predators:

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

How will the MMPA impact your farm?

If the MMPA came into force even as recently as five years ago, there likely would have been significant risks to fish welfare due to increased predator attacks. However, recent advances in acoustic technology and a more blended approach to acoustic and netting solutions means farms, fish and other marine mammals can all thrive within the new MMPA regulatory framework.

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