INTRODUCTION
CONTAINMENT SPECIAL
THE ENVIRONMENTAL DIVIDENDS OF EFFECTIVE CONTAINMENT
WHY PREVENTING ESCAPES IS SUCH A VITAL ISSUE By Malcolm Dickson
T
here is no doubt that the effective containment of farmed aquaculture animals has become one of the key issues affecting the sustainable development of the Scottish aquaculture industry.
While, in days gone by, escapes were treated as mainly an economic issue by fish farmers – because of the loss of valuable fish – the unintended release of farmed fish into natural environments has become one of the main points of conflict between the aquaculture industry and oth- ers. In particular, it is criticised by those with a responsibility or an interest in protecting wild fish populations. The Renewed Strategic
Framework for Scottish Aqua- culture sets out an important environmental principle: farmed fish and shellfish in- dustries should act as a good neighbour by minimising risks
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to biodiversity and impact on the environment and other aquatic activities. ‘Improved containment’ is also one of the Strategic Framework’s five main policy themes, to be achieved ‘by adopting best practice to reduce stock loss, improve profitability and secure the future credibility of the industry whilst minimising adverse environmental im- pacts and preventing conflict with other interests.’ There is no doubt that the importance of effective containment has been recognised by the Scot- tish aquaculture industry and its regulator, Marine Scotland. It is worth reviewing why containment has risen to the head of the aquaculture policy agenda. Firstly, it has been argued that the aquaculture industry had, until ten or so years ago, a poor record on fish escapes. Many thousand salmon and trout were escap- ing from fish farms each year
because of cage damage, poorly constructed or main- tained cages, poor handling practices or specific incidents such as floods. The statistics in recent years have greatly improved. However, as can be seen from the table on page 7, there is a high degree of variability between years.
Genetics
The main alleged nega- tive impact from escaped fish is contamination of the gene pool of unique wild fish stocks. This only applies to salmon escapes, as rainbow trout only rarely reproduce successfully in UK and halibut spawning areas are located well away from farm sites. Farmed salmon are general- ly a different genetic strain to the wild stocks in their vicinity. In the 1980s most salmon hatcheries and broodstock farms focused on developing ‘low grilsing’ stocks – reduc-
ing the percentage of fish that matured after only one winter in the sea. This could be achieved the slow way, by breeding from existing stocks, or by importing new strains of fish, such as the Norwegian MOWI strain that naturally had a very low grilsing rate. The result was that most farms carried salmon with a genetic make-up very different from fish in the local rivers. As the industry gradually developed, broodstock and hatchery operations became larger and more centralised – again meaning that the stocks used on grow-out farms bore lit- tle resemblance to wild fish strains.
However, there are many question marks over the fate of escaped farmed salmon – whether they can survive in the wild, if they can make their way up-river for spawn- ing migrations and if they can successfully interbreed
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