Sea lice, disease and escapes affect the fragile ecosystem
SCOTLAND'S marine ecosystem is fragile and multi-layered and industrial salmon farming can cause damage in a number of different ways. Sea lice, for instance, have a broader impact than their effect on farmed salmon.
Fish farms can produce high enough densities of these to affect not just farmed fish, but to kill wild salmon and trout too.
One solution to the sea lice problem is to bring in so-called cleaner fish that feed on them.
Some of these are captive bred, but many more are wild wrasses caught in designated Marine Protected Areas.
The problem here is that they can also pick up disease, so hundreds of thousands of them are killed every year as the salmon are slaughtered.
Salmon are also predatory fish. Their diet can include soy and wheat, but they also need to eat oily fish or krill. In another move that is environmentally controversial, these are caught in huge quantities across the world and then shipped to Scotland.
This has huge consequences and raises ethical questions, not least for local populations of people who would otherwise have been able to eat these fish themselves.
Scottish farmed fish producers do now include waste from wild fisheries in their feed but they appear unwilling to reduce the fish content of this any further, believing that this helps to maintain the industry's reputation as a natural one.
Yet another issue affecting the sector is that seals are attracted to the salmon in order to feed on them.
They sense the fish through the nets and then bite holes in these in order to reach them.
The result is that the farmed fish can then escape and interbreed with wild salmon, compromising a species which is already in steep decline.
The industry's answer to this problem is to bring in so-called seal scarers to drive them away.
But this technology – used by some 60 per cent of farms – also frightens off dolphins and porpoises.
This is technically illegal in Scotland, but conservationists accuse the regulator, Marine Scotland, of having failed historically to take any action.
One bit of good news on this front is that there does appear to have been a clampdown of late and the fish farming sector says that it has now turned these scarers off.
However, David Ainsley says: “The danger is that farms may now use new generation acoustic startle devices, ignoring evidence that they could also cause illegal disturbance to dolphins, rather that fit the stronger single or double nets used by the more responsible companies. Better netting has the added advantage of reducing escapes, one of the major causes of the decline in wild salmon.
“We want these problems to be sorted out before the industry is allowed to expand further - that's what the parliamentary inquiry recommended years ago.”