Publication Abstract

Development of a system to evaluate the risk of establishment of Gyrodactylus salaris at sites across England and Wales.

R.A. Duguid, J.F. Turnbull, N.G.H. Taylor*, J.E. Bron,  and A.P. Shinn.

The ectoparasite Gyrodactylus salaris has been responsible for large-scale mortalities of juvenile salmon in Norway, where stocks appear to have little or no natural immunity to the parasite. Eradication of the parasite in the wild is difficult and expensive, and the measures used often cause further biological, environmental and economic stress to the affected systems. G. salaris is thought to have spread widely across Europe in recent years. The UK however currently remains free of the parasite. Given the economic and social importance of British Atlantic salmon fisheries, a high priority has been given to design measures to reduce the risk of importation and also to improve contingency plans to better understand and prevent the establishment and transfer of the parasite should it be inadvertently introduced.

The parasite is usually assumed to become readily established in the wild following its introduction, and the majority of Norwegian rivers which have received infected fish have followed this pattern. However, several authors have noted that environmental factors are likely to play an important role in governing whether or not this is the case. Laboratory studies have shown that temperature, salinity, pH and aluminium concentration in particular have an important effect on population dynamics of G. salaris. Empirical field data from several Atlantic rivers in Scandinavia also suggests that the pattern of parasite population growth may differ between locations, and in some instances the parasite may even become naturally eradicated.

The current project has been designed to complement existing work on probable introduction and transmission routes by identifying and evaluating the possible risk factors involved in the successful establishment of the parasite. Work to date has involved collating data on possible factors such as water quality, fish species assemblages and geomorphology at several thousand sites, in addition to Gyrodactylid data from several hundred sites across England and Wales. We will describe the nature of the data which has been collated, outline the modelling work which has begun, and describe future applications of the work, which will include a spatially explicit GIS-based mapping system to predict establishment risk across the region.