© 2006 International Council for the Exploration of the Sea
Interactions between Aquaculture and Wild Stocks of Atlantic Salmon and other Diadromous Fish Species: Science and Management, Challenges and Solutions
An introduction by the Conveners
a Norwegian Institute for Nature Research Dronningens gt 13, PO Box 736 Sentrum, N-0105 Oslo, Norway
b NASCO 11 Rutland Square, Edinburgh EH1 2AS, Scotland, UK
*Correspondence to L. P. Hansen: tel: +47 73 80 1713; fax: +47 22 33 1101. e-mail: l.p.hansen{at}nina.no.
Paradoxically, at a time when there is serious concern about the status of wild Atlantic salmon stocks, the abundance of salmon in the North Atlantic Ocean has probably never been higher as a result of the rapid growth of salmon farming. Since the early 1980s, salmon farming has become a major industry, with production in 2004 of approximately 800 000 t in the North Atlantic and approximately 1.15 million t worldwide (ICES, 2005). Progress has been made in managing the interactions between farmed and wild salmon, and collaboration between farmed and wild salmon interests is now improved. However, wild stocks are in a weakened state, and there are concerns about the disease, parasite, genetic, and ecological impacts of salmon farming on wild salmon stocks. A regime is required under which the industry can continue to prosper, but at the same time, one under which wild stocks are safeguarded so as to maintain the social and economic benefits from both wild and farmed salmon. This has not been and will not be easy.
Currently, the salmon is to the fore but, as aquaculture develops and diversifies into other species, the wild stocks of these species may be affected, and the nature of interactions may be similar. Interactions between cultured and wild salmon are not restricted to those arising from salmon farming. In response to the decline in the abundance of wild salmon stocks, interest is increasing in stocking cultured fish for mitigation, restoration, and rehabilitation. Furthermore, although commercial ranching of salmon is no longer undertaken in the North Atlantic, there is interest in "ranching to the rod" in some rivers. It is necessary to fully consider the likely risks as well as the benefits before releasing any cultured fish into the wild.
In response to concerns about interactions between salmon aquaculture and the wild salmon stocks, NASCO and ICES organized a series of international meetings aimed at reviewing scientific understanding of interaction and providing guidance on appropriate management responses. The first major international symposium on this subject was sponsored by the Norwegian Directorate for Nature Management in Loen, Norway, in 1990 (Hansen et al., 1991). NASCO was sufficiently concerned by the gravity of the threats and their potentially irreversible nature that, in 1991, it adopted guidelines designed to minimize impacts of aquaculture on wild stocks. These guidelines were replaced three years later by the Oslo Resolution, which in turn was replaced in 2003 with the Williamsburg Resolution, developed to ensure that the measures taken by NASCO Parties to minimize the impacts of aquaculture, introductions and transfers, and transgenics were consistent with the Precautionary Approach. The development of the Williamsburg Resolution drew on information presented at a second major international symposium held in Bath, England, in 1997, which reviewed the scientific and management aspects of interactions between salmon culture and wild stocks (Hutchinson, 1997).
Aquaculture is certainly not the only threat to wild salmon stocks, and NASCO is addressing a wide range of other issues relating to salmon conservation and management (e.g. the management of fisheries and habitat protection and restoration) and has recently established an International Atlantic Salmon Research Board to investigate the factors influencing the mortality of salmon at sea. It was felt that the progress now being made in managing the interactions between wild and cultured salmon must be maintained, enhanced, and given more urgency to ensure that all aquaculture practices are conducted in a sustainable manner that does not threaten wild stocks. ICES and NASCO, therefore, agreed to hold a third international symposium in Bergen, Norway, 18–21 October 2005. The objectives were
- to summarize available knowledge of the interactions between aquaculture and wild salmon stocks and other diadromous fish species;
- to identify gaps in current understanding of these interactions and to develop recommendations for future research priorities;
- to review progress in managing interactions, the remaining challenges, and possible solutions; and
- to make recommendations for additional measures to ensure that aquaculture practices are sustainable and consistent with the Precautionary Approach.
The aim was to build on the existing collaboration between farmed and wild salmon interests so as to identify the remaining challenges and possible solutions in moving towards sustainable culture of Atlantic salmon. In all, 111 participants from 17 countries attended the symposium, including delegates with experience of research into and management of interactions between cultured and wild salmon in the North Atlantic Ocean, Baltic Sea, and Pacific Ocean. Although the focus was on interactions between cultured and wild Atlantic salmon, several contributions presented information about other diadromous fish species.
The symposium was opened by Janne Sollie, Director General of the Directorate for Nature Management in Norway, who noted that the understanding of interactions between cultured and wild salmon has increased markedly since the first ICES/NASCO symposium in 1990 and that it is now generally recognized that salmon farming can pose a serious threat to the wild stocks. There is improved cooperation between the salmon farming industry, the authorities, and various stakeholders, and some progress is being made in addressing interactions. However, she referred to two significant events in Norway during 2005, which had resulted in the escape of approximately 600 000 farmed salmon into the wild. She emphasized that additional measures, therefore, are essential to move towards sustainable aquaculture.
The symposium was structured in four plenary sessions and a poster session. The first of the plenaries set the scene with reviews of the value of wild Atlantic salmon, developments in the sustainability of the salmon farming industry, the stock status and management of wild Atlantic salmon, and the ecology of cultured Atlantic salmon and their interactions with wild fish. A number of points emerged from this keynote session, including:
- In addition to the significant social and economic values associated with salmon fisheries and eco-tourism, the general public cares about and is willing to pay to conserve the Atlantic salmon. If the salmon farming industry is perceived as damaging the wild stocks, consumers may reject its products.
- Worldwide production of farmed salmon has trebled in the past decade, and the industry's future success requires that the product is perceived to be safe and healthy, that it is not associated with degradation of the natural environment, and that the industry is perceived as open, transparent, and willing to focus on welfare issues and environmentally sustainable practices.
- Wild Atlantic salmon stocks are very vulnerable, with many stocks in a depressed state and some critically endangered. Much has been done to reduce exploitation, but many factors are influencing the stocks. Given the status of the stocks, it is vital that human activities, including those arising from aquaculture, do not exacerbate the situation.
- Cultured fish compete with wild salmon in nature for space, food, and breeding partners. They may partly displace, increase the mortality of, and reduce the growth rate of wild fish with effects on life history traits, biomass, and production.
Following this keynote session were sessions focusing on genetic and ecological interactions and their management, and on disease and parasite interactions and their management.
From the session on genetic and ecological interactions, it emerged that:
- Although there have been considerable improvements in containment and reporting, the number of escaped farmed salmon is still very large relative to the abundance of wild salmon.
- Escaped fish disperse quickly from the site of release, moving predominantly with the currents; their fate is highly variable and affected by a variety of factors.
- In Norway, the number of salmon in cages appears to be a better predictor of escapees in fisheries and spawning stocks than the reported number of escapees, suggesting that there may be significant unreporting, possibly because of small scale but frequent escapes (trickle losses) during handling, net changes, etc. Storms were identified as a major cause of escapes, and the implications of climate change for future containment management measures will require careful consideration.
- Theoretical modelling, comparing wild salmon populations exposed to salmon farming with those not exposed, indicates reduced productive capacity of wild salmon in areas with farms, with the size of the reduction linked to the scale of farmed production.
- Genetic change has been observed in some wild salmon populations exposed to escapees but not in others, suggesting that impacts from aquaculture are influenced by the number of escapees spawning and the abundance of the wild fish population in the river. Simulations, based on simplified input data with fixed annual intrusion rates of 20% farmed escapees, suggest that substantial changes can take place in wild salmon populations within ten salmon generations and that these changes may be irreversible.
- Risks are posed by the stocking of cultured fish, and the goals of such programmes need to be carefully considered.
- Solutions to escapes from freshwater facilities are available and are inexpensive to implement. Improved physical containment measures required for marine sites and biological containment should be considered.
From the session on disease and parasite interactions, it emerged that:
- Increased understanding of all aspects of the biology of sea lice, which has led to better tools for identification of sea lice, is facilitating the development of increasingly effective integrated louse management strategies and may lead to the development of an effective vaccine in future.
- Sea lice infestation pressure from salmon farms is an important issue affecting wild salmonids in many areas. Infestation levels on emigrating salmon smolts are highly site-dependent, and the risk of infestation varies from year to year and with hydrographic conditions, etc.
- Sea trout are highly susceptible to sea louse infestations, with susceptibility decreasing with distance from marine salmon farms.
- For salmon and sea trout, the burden of sea lice is now recognized as a strong predictor of mortality in areas with farms.
- Sea louse management has evolved considerably in recent years, but there are concerns about the reliance on a handful of key medicines. Although there have been notable improvements in louse management strategies in recent years, challenges remain if wild salmon and sea trout stocks are to be effectively protected. The use of wrasse may be an important option in integrated louse management regimes.
- It is essential to prevent the further spread of the parasite Gyrodactylus salaris and to eliminate it from infested rivers.
The final plenary session was a synthesis session intended to highlight the remaining challenges and their possible solutions. Following a summary of the preceding sessions by each Session Chair, six participants from different interests were asked to give their perspectives on the information presented during the symposium, i.e. their "take-home" messages. There were two representatives of non-governmental organizations, two representatives of the fish farming industry, and two representatives of administrations involved in the management of salmon farming or wild salmon. In their messages, the salmon farming industry representatives acknowledged that it can no longer be claimed that salmon farming does not pose a threat to wild salmon, but the industry has evolved considerably, and there are causes for optimism based on evidence that good farm management can ensure that the wild and farmed salmon sectors can coexist in harmony. The key challenges remaining include the introduction of further measures, including effective area management and fallowing to protect wild salmon and sea trout stocks from sea lice, and measures to minimize escapees, including improved cage designs, risk assessments, awareness campaigns in relation to trickle losses, and third-party audits. Furthermore, they recognized the need to avoid confrontation and to build trust by seeking constructive dialogue and developing increased cooperation between wild and farmed salmon interests. That process has started, and we hope that the emphasis now will be on moving forward with solutions to the remaining issues.
The symposium was closed by Peter Gullestad, Director of the Norwegian Directorate of Fisheries and a vice-president of ICES.
In all, 35 invited and contributed papers and 13 poster papers were presented. This publication contains those papers that were submitted to the ICES Journal of Marine Science and accepted following peer review under the direction of Peter Hutchinson, Guest Editor. We have prepared a separate report containing our conclusions, the conclusions of the Session Chairs and the take-home messages. The Conveners express their sincere thanks to the symposium Steering Group: Malcolm Beveridge, Mary Colligan, Tom Cross, Knut Hjelt, Peter Hutchinson, Arni Isaksson, Geoff Perry, and Chris Poupard. The excellent work of Peter Hutchinson in editing these proceedings is also acknowledged. The Conveners also thank the participants who provided their take-home messages during the final session: Katherine Bostick, Fiona Cameron, Knut Hjelt, Jens Christian Holm, James Ryan, and Øyvind Walsø.
Finally, ICES and NASCO acknowledge with gratitude the generous support of the following organizations:
Research Council of Norway, Directorate of Nature Management (Norway), Directorate of Fisheries (Norway), Norwegian Institute for Nature Research, Royal Norwegian Ministry of Fisheries and Coastal Affairs, Royal Norwegian Ministry of the Environment, Scottish Executive, Defra (UK), Fisheries and Aquaculture Research Fund (Norway), Directorate of Freshwater Fisheries and Salmonid Enhancement Fund (Iceland), National Marine Fisheries Service (USA), the Worshipful Company of Fishmongers (UK), Atlantic Salmon Trust (UK), Intervet International BV (the Netherlands), Marine Institute (Ireland), Pharmaq AS (Norway), ScanVacc AS (Norway), Norwegian Farmers Union, Norwegian Salmon Rivers, and the City of Bergen.
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In Hansen L.P., Håstein T., Naevdal G., Saunders R.L., Thorpe J.E. (Eds.). Interactions between cultured and wild Atlantic salmon. Proceedings of a symposium hosted by the Directorate for Nature Management and Norwegian Institute for Nature Research held in the Hotel Alexandria23–26 April 1990Loen, Norway (1991) Aquaculture 98:(1991) 1–324.
In Hutchinson P. (Ed.). Interactions between salmon culture and wild stocks of Atlantic salmon: the scientific and management issues. ICES Journal of Marine Science (1997) 54:963–1225.
ICES. (2005) Report of the Working Group on North Atlantic Salmon (WGNAS)5–14 April 2005Nuuk, Greenland ICES CM 2005/ACFM:17.
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