1st International Sea Trout Symposium

Immediate action to protect and conserve sea trout stocks throughout their geographical range was urged by 150 delegates from 15 countries represented at the Symposium. Research findings threw new light on the genetics and ecology of sea trout, stressing the need for urgent action to realise its full conservation and socio-economic value.  The Symposium warned that if governments, state agencies, and other potential stakeholders continue to neglect the science and management of this resource, at a time when some stocks are collapsing and others are subject to increasing attention and exploitation, then another valuable natural resource will be damaged by man. It identified a need to respond positively in three areas.

Increased Recognition of the Status and Value of Healthy Sea Trout Stocks

  • The native European trout represents a unique combination of life history diversity and range of habitat use in freshwater, estuarine and coastal waters. The life history of the sea going form, the sea trout, spans all three environments and makes it therefore a key sentinel species. Furthermore, this range of life-histories adds significantly to the biodiversity of all waters, including the many smaller, often neglected, streams which are home to juvenile sea trout.
  • The interaction of genetics and environment which triggers some juvenile trout to migrate to sea while others choose to remain in freshwater is a prime example of the complex interactions which govern the overall aquatic environment. A detailed understanding of the biology of the sea trout will prove particularly valuable in assessing ecosystem health in the context of the Water Framework Directive.
  • Sea trout often return to rivers in very large numbers. Many adults can attain a very large size, often equivalent to salmon. These larger sea trout are usually long-lived and display a unique ability to survive repeated spawning migrations between the marine and freshwater environments. This natural resource is of major importance to both recreational and commercial fisheries and can provide considerable social and economic community benefits – particularly in rural areas.
  • Knowledge of the socio-economic benefits of sea trout has been largely ignored in the past and now lags well behind that available for salmon, at a time when such information is needed in several important contexts. It is crucial that research in this area is commissioned.
  • The sea trout is commonly regarded as being of secondary importance to the Atlantic salmon. The Symposium concluded that its unique biology, robust and opportunistic life history and ubiquitous distribution all represent potentially valuable assets that should be more widely recognised and used. Sea trout stocks and fisheries should be managed so as to attain a status equivalent to that of the Atlantic salmon.

Priorities for Improved Management of Sea Trout Fisheries

Although stocks of sea trout appear to be doing reasonably well in some regions, serious stock collapses have occurred elsewhere and in some regions stocks are endangered or at risk of local extinction. Examples of stock failures caused by over-exploitation, parasite infestation by sea lice linked to marine fish farming operations and degradation of the freshwater habitat were all presented.

Recent research and advances in technology have created new opportunities and challenges to improve management policies, practices and procedures. The following management priorities were identified: –

  • The need to protect the larger adult female sea trout, which often make a disproportionately high contribution to egg deposition and which may be the genetic repository for the trait of seaward migration that characterises the sea trout.
  • The need to recognise the importance of protecting the smaller rivers, sub-catchments and streams generally favoured as spawning and nursery grounds by sea trout. Such habitats often generate a disproportionately large number of the adults produced in most systems. Their small size makes them often fragile and vulnerable to environmental damage and they may require special designation and protection.
  • The Symposium noted that many sea trout stocks in salmon aquaculture areas in Western Ireland and Western Scotland had suffered stock collapses and concluded that recovery of these stocks will largely be dependent upon continuous effective control and management of sea lice on marine salmon farms in these areas.
  • The need to monitor more closely rod and net fisheries in freshwater, estuarine and coastal zones, in order to better assess their impacts on sea trout stocks. Existing regulations should be reviewed to assess their efficacy to prevent illegal fishing or over-fishing in licensed salmonid fisheries, and to eliminate sea trout by-catch in other coastal and estuarine fisheries.
  • The need for integrated scientific advice that takes account of other species of fish and a wide range of ecosystem components.
  • The need to avoid the risks of introducing potentially harmful genetic damage by stocking with domesticated strains of farmed trout in waters frequented by wild trout. It was noted that stocking with first generation, native strains of juvenile trout to restore, maintain and enhance wild sea trout populations has proved useful in some countries. Where this is not yet possible, a precautionary approach should be adopted for all trout stocking programmes.
  • The need for more complete, accurate and systematic catch statistics for both the recreational and commercial sea trout fisheries. Data are either unavailable or of poor quality in many regions. The inclusion of information on stock composition and fishing effort is considered to be essential to complement and interpret basic catch data. Automatic fish counter systems need to be able to distinguish sea trout from salmon.

Priorities for Research to Improve Understanding and Management Ability

Considerable progress has been made in several scientific fields that could now allow rapid advances in sea trout research that were previously impossible or impracticable. The Symposium presented exciting new developments in genetics, genomics, populations dynamics, the statistical and ecological basis of Biological Reference Points and in Geographic Information Systems. These could provide a scientifically robust framework for practical assessment, modelling and decision-making. The major strategic priorities for further research and investigation were identified as follows: –

  • To explore, with novel techniques described at the Symposium, how genetic and environmental factors interact in determining incidence of the sea going migratory habit.
  • To develop understanding of stock-recruitment processes in trout, including interactions with other species, particularly salmon, in a wide range of stream types.
  • To gain a better description and understanding of the structure of sea trout stocks in different geographical regions and to quantify temporal changes in the structure and composition of index stocks. Such future studies, which should include a representative sub-sample of the many smaller river systems, will improve understanding of factors determining migratory behaviour, and stock response to environmental and fishery changes.
  • To develop and promote stocking practices that are protective of wild stocks and operationally effective, when their application is essential for management purposes.
  • To further develop models that describe the relationship between habitat availability, quality and utilisation, particularly in spawning and juvenile nursery areas.
  • To refine estimates of the socio-economic value of sea trout and brown trout fisheries and their potential for sustainable development.
  • To investigate the movements and feeding migrations of post-smolts and adults in estuarine and coastal waters and to examine the nature and extent of any overlap between the coastal feeding zones of sea trout stocks from neighbouring rivers.

Much of the work outlined here will require commissioning and supporting long-term studies on trout genetics, ecology and population dynamics, and this work should be integrated with catchment-scale, multi-disciplinary ecosystem studies. Such large-scale research is necessarily collaborative. The Symposium noted with regret that similar recommendations from previous meetings in 1984 and 1994 had not been progressed. In a wider European context, it was noted that our limited understanding of fundamental sea trout biology is still too dependent on a very few facilities where these long-term studies have taken place. When dealing with a species that exhibits such a flexible and variable pattern of life history and behaviour as the trout, the risks of extrapolating data between regions are even greater than those that apply to the Atlantic salmon.

The formal proceedings of the Symposium will be produced as a peer-reviewed publication in 2006. In order to make timely progress, it was recommended that the preliminary conclusions summarised here should be presented to the Diadromous Fish Committee of the Council for the Exploration of the Sea at its next meeting at Vigo, in Spain, this autumn for immediate discussion, seeking support and practical development of these preliminary recommendations.

Nigel Milner & Graeme Harris
9th August 2004
Symposium Convenors