Controlling the uncontrollable? The battle against sea lice.

Few things cause as much controversy on Canada’s British Columbia coast as salmon aquaculture. In late August 2016, Musgamagw Dzawada’enuxw First Nation handed eviction notices to Cermaq and Marine Harvest salmon farms that occupy their territory. “We have heard the words of Prime Minister Justin Trudeau, that honoring the rights of First Nations are a ‘sacred obligation’ to the Liberal Government of Canada”, hereditary leader and chief councilor Willie Moon affirmed. “Our people have spoken, we want salmon farms out of our territory.” Sea lice and their impacts on wild salmon, lay at the heart of their objections.

The problem with sea lice

Credit 7Barrym0re/Wikimedia (Public Domain)

Credit 7Barrym0re/Wikimedia (Public Domain)

Sea lice are small ectoparasitic copepods that attach onto the scales of fish, feeding on tissue, mucus, and sometimes blood. In naturally occurring systems, lice infestation usually occurs in adults whilst they are at sea. Since sea lice cannot survive in fresh water, they fall off the adult salmon or die when they return to freshwater spawning streams. The problem for farmed salmon is that they are confined to a limited area. If a louse originating from a wild salmon infects a farmed salmon, the farmed salmon never migrates to freshwater and so can’t shed the lice. In farmed salmon, typically kept in high densities, lice can easily increase to levels not normally experienced in the natural environment. When wild salmon swim past these infested farms, the lice from the farms easily infect the wild salmon – and at higher rates than the wild salmon would normally experience. Since many salmon farms are located on migration routes, wild juvenile salmon, who would not normally encounter high levels of sea lice, also become infested. A single salmon farm could increase sea lice pressure on juvenile salmon migrating past by as much as 73 times above ambient levels. As the juveniles continue their migration out to sea, the lice carried with them reach maturity, reproduce, and re-infect, potentially spreading to other wild salmon that may have never encountered the original farm.

When salmon are infested with very high levels of sea lice, their health can be severely impacted, and may even be fatal – especially if the salmon are juveniles. Heavily infested juvenile sockeye salmon face greater risk of starvation because they cannot get enough food. Exactly how lice cause this issue is still being investigated, but it is thought that lice could impair the salmon’s swimming ability, or restrict its sight. The more juvenile salmon that die during their time at sea, the fewer migrate back to freshwater breeding streams to produce the next generation, the fewer salmon hatch the following year. Recent research showed how in 2015, sea lice infestation rates on wild pink salmon in British Columbia’s Broughton Archipelago reached exceptionally high levels, which in turn is thought to have increased wild pink salmon mortality by 9% – 39%.

Just as infestation rates proliferate in individual farms because of the high stocking density of the salmon, infestation rates between farms and wild salmon also increase as the density of farms increases, and when farms are located near fish holding facilities. A simple response might be to spread salmon farms out, though this may not necessarily be realistic for aquaculturalists, or even possible given how busy some areas of the ocean are now becoming. Spreading farms out may also simply spread sea lice and other infections to other parts of the ocean. Within farms themselves, the question of how much salmon is too much from an environmental and animal welfare concern is a subject of continued debate.

SFU doctoral biology student Sean Godwin has found evidence that sea lice weaken juvenile Fraser River sockeye salmon's ability to forage for food. Credit  Lauren Portner/Simon Fraser University/Flickr (CC BY 2.0)

SFU doctoral biology student Sean Godwin has found evidence that sea lice weaken juvenile Fraser River sockeye salmon's ability to forage for food. Credit  Lauren Portner/Simon Fraser University/Flickr (CC BY 2.0)

“We need help”

Tackling lice is an ongoing concern for the industry – and an expensive one. When at the 2014 North Atlantic Seafood Forum in Bergen Alf Helge Aarskog, CEO of Marine Harvest, was asked what the industry’s biggest issue was, he had little trouble providing his answer: “Whoever solves sea lice, come and see me, because we need help.” Industry has traditionally relied on medicines or chemicals to rid salmon of lice, however these have their own issues. For example SLICE®, is a chemical added to salmon feed. As it is digested, it passes into the salmon’s tissues and is then absorbed by any attached lice which die shortly after.   As not all the feed that enters pens is eaten, much of it is lost to the natural environment where it can accumulate on the ground. Here it could impact other species, like altering gene expression in spot prawns. Other treatments like hydrogen peroxide have been linked to increased salmon stress. Similar to antibiotic overuse, the overuse of chemical and medicinal sea lice treatment led to concerns about ‘drug-resistant sea lice’. In Norway, routine antibiotic use for disease control has been replaced with vaccinations and improved farming techniques aimed at improving hygiene. As well as benefiting the environment and the salmon, reduction of antibiotic use is also beneficial for human health. The first ‘vaccine’ for sea lice was launched in November 2015 in Chile, where it has already shown some success at lowering sea lice infestation – and consequently, chemical use in salmon farms.

Alternative approaches

Concerns surrounding the impact of chemicals in aquaculture has helped to spur a number of alternative techniques for tackling sea lice in farms. Placing other fish, such as lumpfish or ballan wrasse which eat sea lice, inside salmon pens is effective. Other approaches are more technological, such as the ‘Stingray’ system which uses a laser that detects lice on the salmon, locks on and fires a short laser pulse at the louse, killing it with no harm to the fish. Novel net-pen designs, such as ‘snorkel sea cages’ which reduce infestation by keeping salmon at lower depths than sea lice larvae, could also help prevent outbreaks.

Of course the safest solution would be to prevent infection in the first place. Keeping salmon farms out of areas used by wild salmon has been suggested as a viable solution, but keeping them out of the ocean all together would be even better. Recirculating Aquaculture Systems (RAS) vary in design but work on similar principles. Water in the fish tank is taken through a series of filtration processes to remove waste, and then onto a detoxifying treatment area, and the resulting clean water pumped back into the fish tank. Apart from the initial input of water, only small additions are required to maintain the process.

One of the few commercial land-based salmon farms can be found in British Columbia. KUTERRA, owned by the Namgis First Nations, sold its first harvest in early 2014, and later that year received “Best Choice” accreditation from Monterey Bay Aquarium’s ‘Seafood Watch’ sustainable fisheries certification program. Whilst KUTERRA’s capital costs were much higher than open-net salmon farms, they argue that today capital costs would be much lower, as much of these costs went towards developing and testing their system. They also claim to have operational costs on par with net-pen farms. The economic success of commercial closed containment salmon farms like KUTERRA are likely to be monitored with great interest by industry, managers and concerned stakeholders. Even if they prove to be a feasible alternative to net-pens, their implementation may very well face another challenge – availability of land to put the farms on.

Example of a Recirculating Aquaculture System. Credit Narek75/Wikimedia (CC BY-SA 4.0)

Example of a Recirculating Aquaculture System. Credit Narek75/Wikimedia (CC BY-SA 4.0)

This article also appears at The Sustainable Food Trust.