The cultivation of Atlantic salmon has become a major industry in both Europe and North America in the course of the last 25 years. During the 1980s scientists and managers became aware that substantial numbers of farmed salmon had escaped from aquaculture facilities and were present among wild stocks. There has been mounting concern in the meantime that interactions between wild and farmed salmon might prove to be deleterious to the wild stocks, leading to changes in their genetic composition, the introduction of diseases and parasites, and other effects with negative ecological consequences.
Dr Malcolm L. Windsor, Secretary of NASCO
By 1994 NASCO was sufficiently concerned about the serious nature of the threats and their potential irreversibility to establish guidelines to protect the wild stocks that were agreed by all its North Atlantic member governments. The very successful salmon aquaculture industry continued to grow rapidly in the 1990s, and the numbers of cultured salmon in the wild continued to cause concern. In some rivers flowing into the North Atlantic, 90% of the salmon were of farmed origin. These levels were unusual but there were many rivers where a substantial proportion of the fish were not of wild origin. Even on the high seas and in the area close to the Faroe Islands almost 40% of some catches consisted of farmed salmon. Knowledge regarding the interactions was growing though still far from complete. In recent years it has become increasingly important for governments, the salmon aquaculture industry on the one hand, and those concerned with managing wild stocks on the other, to decide what the next steps should be: in particular how the genetic integrity of the wild stocks could be protected and the effects of disease and parasitic infections and other man-made impacts minimized whilst, at the same time, ensuring the continued presence and growth of a viable salmon aquaculture industry.
Therefore ICES and NASCO agreed to hold an international symposium from 18 to 22 April 1997 at Bath, England, to evaluate the state of current knowledge of these interactions and to consider the implications for management and for future research. The Co-Conveners, Dr Lars Petter Hansen, Alan F. Youngson, and I, were most fortunate to obtain very generous financial sponsorship from the Directorate of Nature Management, Norway, and from the FAIR Programme of the European Union as well as support from a number of other agencies. Invaluable support was also contributed by members of the Scientific Steering Committee: Professor Noel P. Wilkins, Professor Lars-Ove Eriksson, Dr Árni Ísaksson, Dr Henry E. Booke, and Dr Robert H. Cook.
More than 170 participants from 18 countries attended, and there were delegates with knowledge and experience of the situation not only in the North Atlantic but also in the Baltic Sea and the Pacific.
There were seven sessions: Keynote Speeches; Genetic Interactions; Ecological Interactions; Disease and Parasite Interactions; The Genetic Problem and Practical Solutions; Management Implications; and Synthesis and Management Considerations. In total 46 papers and 15 posters were presented. Under the direction of Dr Peter Hutchinson, acting as Guest Editor, the proceedings will be published in the December 1997 issue of the ICES Journal of Marine Science, produced by Academic Press.
At the Symposium many participants expressed concern about the potential impacts on wild salmon stocks of accidental as well as intentional releases of fish. This applies to farmed salmon as well as ranched or stocked fish. Salmon escape from fish farms in all areas where fish farming occurs and the incidence of farmed salmon in fisheries and rivers is highest in areas where the density of farms is highest. Sea ranching with non-indigenous stocks or based on releases from marine localities and small rivers corresponds to mass escapes of smolts from fish farms. Managed inappropriately salmon ranching is a potential threat to wild salmon stocks. The stocking of young salmon for enhancement purposes was also questioned, as in several areas this was carried out with non-indigenous fish or with offspring of salmon of unknown origin entering fresh water to spawn.
There is a strong risk that irreversible genetic changes will occur in wild salmon populations if large numbers of escaped farmed fish interbreed systematically over several years. The risks would be especially severe if transgenic fish were ever used in sea cages. Furthermore, offspring of reared salmon that have been selected for high growth rate may grow more quickly as parr and thus displace slower growing wild fish. This could lead to changes in the relative fitness of salmon throughout the life cycle. Fish farms may also be contributing to an increase in the overall abundance of pathogens and significantly affect the epidemiology of those pathogens. There is a complete lack of the use of the precautionary approach in the whole complex of interactions between cultured and wild salmon in that the interactions are proceeding without knowledge of their impacts.
The Symposium showed that great gains in knowledge have been made over the last few years and that interactions between cultured and wild salmon pose a more serious threat to wild salmon than had previously been believed. The threat is particularly serious from farmed salmon because of the very large amounts of fish that are produced compared with ranching and stocking. However, it must be noted that through development of effective vaccines the fish farming industry has significantly reduced the problems with some of the serious diseases. The Co-Conveners feel that it is urgent that interaction between farmed and wild salmon stocks be eliminated or, at the least, greatly reduced. The most effective measure that can be introduced in the short term is the use of sterile fish only in the sea. In the longer term the farming technology must be improved so that virtually no fish can escape.
The Symposium made a very valuable contribution by reviewing the latest scientific information, airing the arguments for management measures, and allowing the views of all sides to be heard. A number of such measures by salmon managers and by the salmon farming industry were outlined.
The proceedings were enlivened by a special performance of the NASCO band, which had previously performed at the 1996 NASCO Annual Meeting in Gothenburg. On this occasion it comprised Dr Ingemar Olsson on accordion and Dr Árni Ísaksson on piano. They played at the Symposium Dinner and were very warmly received. It made a nice break from genetics!