Impact of underwater cages on marine life

In off-shore fish farms, stocks are raised in large cages suspended in the sea until they are a suitable size for sale. The theory is that faeces and uneaten food as well as chemicals and APIs used to treat fish sink through the cages and are dispersed by tidal action.

Although this may have been the case 50 years ago when salmon farming first started in Scotland, the current situation is that with so many fish farms along the Scottish coast, concerning levels of pollution can occur.

This has led to aquaculture being blamed for not only the pollution that some careless producers are responsible for, but all manner of other woes as well.

Preventing sea lice infestation

Sea lice do not affect humans – but occur naturally in the wild. Two recent scientific surveys have shown that a small percentage (around 1%) of wild Atlantic salmon will die from sea lice infestation annually.

However, captivity – even in pens where the water may be constantly being refreshed – brings with it a greatly increased risk of infestation – potentially leading to massive stock losses as infestations can be fatal if untreated quickly.

Aquaculture companies use a variety of methods to treat sea lice but one of the most successful involves removing stocks from pens and immersing them in pesticide at a fairly high concentration for a short length of time. The fish are then returned to the opens whilst the ‘wash water’ is disposed of – as it cannot be flushed to the ocean, due to environmental regulations.

Clean-up of wash water

Currently most wash-water created as a by-product of sea-lice control has to be removed from barges into holding tanks and then sent for incineration. This is because most fish producers do not have the land-based infrastructure to treat this highly-polluted water. Often it ends up being trucked many hundreds of kilometres to an incineration plant – far from ideal for a company’s carbon footprint – or their CSR!

As an alternative, Arvia’s water-polishing systems can actually treat this highly polluted water – either in situ on the service barge or on land, making it possible to recycle the water back to the ocean or to be used again in sea-lice control or other operations.

Arvia’s Rosalox™ systems use a unique combination of adsorption and oxidation and can remove many recalcitrant compounds down to parts per trillion levels.

We have tested our systems with pesticides and antibiotics extensively used for sea lice control in Scottish salmon farms – and gained some impressive results.

Additionally, Arvia’s unique water polishing systems are robust and compact and follow a modular design ethos, allowing them to be installed on barges or tenders or in larger arrays, in shore-based facilities.

Removal of pesticides/insecticides

Sea lice are not the only issues faced by farmed salmon in off-shore pens. They also include CMS (cardiomyopathy syndrome), Pasteurella skyensis, PD (pancreas disease) and algal bloom.

In many cases, pesticides and/or insecticides are also used and Arvia’s sytems are just as suited to treating water water from these processes.

It’s critical to reduce the risk of AMR (anti-microbial resistance) in fish stocks so that treatments are effective and long-lasting.

Pillars for sustainable fish farming

In fact, the EU’s own pillars for sustainable fish farming are:

1. Economic: aquaculture must be a viable business opportunity with a positive long-term outlook
2. Social: Aquaculture must be socially responsible and contribute to community health and well-being
3. Environmental: aquaculture should not create significant disruption to the ecosystem or be responsible for the loss of biodiversity or significant pollution impact

Whereas many off-shore facilities struggle to meet these requirements, even allowing for the additional cap-ex and the inevitable embodied carbon and cap-ex of a new-build onshore facility, RAS (Recirculating Aquaculture Systems) seems to point the way forward.

Whilst historically, RAS was only for high value stocks, smolt or sport fish, recent innovations are opening up the viability of this type of installation.