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Many may assume that the effects of a few farmed fish escapes to overall wild stocks will be as influential as a drop of water is to the ocean, but figures and statistics now available have put the size of the issue into true perspective, writes Adam Anson for TheFishSite.

Whilst little is understood of the wider issues and implications at stake for most aquaculture species, salmon research has been relatively extensive.

According to a Food and Agriculture Organisation report, which studied the incidence and impacts of escaped farmed salmon, recent analysis has estimated that two million Atlantic salmon escape from fish farms each year - a figure equivalent to half the total number of wild salmon in the sea.

This relatively large number has larger effects still over time. A report released by the Pure Salmon Campaign says that as much as 90 per cent of the salmon in some rivers of the Faroe Islands, Norway, Scotland, Ireland and Canada are "fugitives of their progeny". Later, the report claims that whilst escapees from New Brunswick's Magagaudavic River only accounted for 5.5 per cent of the overall wild population, by 1995 that figure had leapt to 90 per cent.

Other figures from the report suggest that these escapees are also beginning to spread out and invade new areas - occupying 18 rivers of the British Columbia in 1995 and 77 rivers when re-examined six years later.

Although it can be argued that these escapees will add to struggling wild fish stocks, it must be taken into account that, due to overfishing, wild salmon stocks are in decline the world over and that this level of decline occurs irrespective of escapes. Researchers tend to be in agreement that wild salmon stock are not being boosted by escapes, they are in fact being replaced by them. This is believed to be true of all farmed fish and their wild counterparts.

The problem comes to light in consideration of how the farmed fish differ from wild fish and how they interact with them. According to the Pure Salmon Campaign "virtually all factory farmed salmon are descended from 40 original stocks of Norwegian Atlantic salmon." Successive breeding has selected certain traits in these farmed salmon that are beneficial to the producer, creating fast-maturing, large fish. However, this process has also brought about agressive salmon that are more physically dominant than wild fish.

In the earlier stages of their lives they will out compete wild fish for food, habitat and mates, but over the long term these are genetically inferior fish, less adapted to the various geographical regions they may come to inhabit and less likely to succeed. Interbreeding between wild fish and farmed fish is therefore detrimental to the stock as a whole. The well designed genetic characteristics of the wild fish become contaminated and overall genetic variability will be reduced.

Another detrimental and well documented affect of escapes is the transmission of pathogens from farm to wild. Fish farms undergo major battles against disease and parasites, which have a tendency to cultivate and grow rapidly out of control. Ocean borne diseases and pathogens spread very quickly once they get hold of a school. Diseased fish escaping from farms have the potential to seriously infect wild stock and push them to extinction.

The Root of the Problem

Aquaculture pens generally consist of a huge net raising up out of the sea which is open at the top. Fish losses often occur from simple poor maintenance of pens, which allows for a small leakage of fish every so often and amassing to a much higher number over the course of a year. However, fish can also escape in huge numbers during rough seas and high waves, which can damage the pen, or wash fish over the top. In 2005, a single incident saw half a million salmon escape from a Norwegian farm, whilst a similar incident in Chile led to the escape of one million.

Ian A. Felming, University of Newfoundland, said that the risk posed by escapees depended on the probability of escapes, the magnitude of escapes, the frequency of their occurrence and the probable impact on wild populations and ecosystems that they may have. Commenting on a study conducted on British Columbian fish farms, Mr Felming reported that 42 per cent of escapes were due to simple net failings, four per cent to hardware failings, 15 per cent to boat events and 39 per cent to handling.

Another presentation, provided by Arne Fredheim of Sintef Fisheries and Aquaculture, summed up the failings in four causes: operational (changing of nets); human error (error in attachment); technical failure (fatigue, wrong dimensions); and design failure (wrong method, error in weather data, understanding of all implications). According to Arne Fredheim problems lie directly in increased net sizes, more powerful cranes, nets that are not cleaned for biofouling and pulling at the wrong rope. Solutions then lie in human-proof, life-long system designs and technical training, concluded Mr Fredheim.

Whilst it may be considered that careful design should eradicate the problem altogether a presentation made by the Norwegian Institute for Nature Research recently stated that irrespective of what is done to prevent escapes, it is impossible to avoid them altogether. Rather than focussing on preventing them, a better approach may be to reduce the impact that they have.

Problem? What Problem?

One simple solution to escaped fish is simply to go out and re-catch them. However, so far this has proven tricky. Efforts to recapture salmon have been generally low, usually only accounting for a few per cent of the original amount lost. Interestingly, the recovery rates of farmed cod appear to be significantly higher. Recent trials have indicated that this figure could be as high as 30 - 40 per cent. It seems that the behaviour of the type of fish that is farmed could have big implications on reducing the rate of escape.

It has also been suggested that if the genetic make up of farmed fish was similar to the relative geographical wild stock then fish escapes could actually be beneficial to it. However, it may be deemed improbable that fish farmers will relinquish their high vale fish stocks in favour of one that is more costly to raise. It must also be taken into account that any positive effect of escaped farmed fish relies on the assumption that they have no negative genetic effects, do not transmit disease and do not out-compete the wild stock.

A solution to eradicating all gentic risk would be to make farmed fish sterile. Enhanced biosecurity is an obvious option to reduce disease and parasite transmissions, but this has proven difficult to achieve and efforts to do so with antibiotics and chemicals have resulted in severe environmental repercussions and high levels of stress in the farmed fish treatment has been used upon. According to the Pure Salmon Campaign, the global salmon industry has largely ignored public criticism and resisted tagging measures whish would aid new discoveries of the causes and effects of escapes for all species of farmed fish. The campaign also believe that government regulations have been very relaxed and there has been no effort to identify measures taken to avoid escapes with product labelling.

Whilst a complete solution may not be currently available, it is clear more research needs to be done to assess both impacts and solutions.

April 2009

the Fish Site Editor

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