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Research Document 1998/161

A review of the potential effects of sea lice infestation among aquaculture salmon on wild salmon

By A. McVicar

Abstract

The prevention of Lepeophteirus salmonis infection on farmed salmon is likely to be an unachievable objective, at least in the foreseeable future. Although conclusive evidence is lacking, it is realistic to assume that lice from farmed salmon will contribute to lice in wild fish populations. The extent of this contribution and the consequences are the areas of current intense controversy. Much of this controversy can be attributed to an inadequate data-base. There is a concerning tendency for researchers to be selective in the interpretation of available data and to take highly polarised stances where any proper consideration of an alternative interpretation is avoided as being a sign of weakness of their position. It is essental that realistic dialogue between different groups involved in this topic area is fostered at every opportunity.

The general absence of historical (pre-fish farming) data on lice levels in wild salmon populations, and of an adequate more recent time-series on fish farms, prevents evaluation of temporal changes in lice levels and the factors (including farms) which may be contributing to these. Similar difficulties are found with spatial variations in lice levels. The pathogenicity of lice to salmon is well established in experimental and farm situations, but such information is difficult to obtain for wild populations. A focus of effort on achieving a reduction farm lice levels and on understanding the biology of transmission of infection to new hosts could maximise output from resources allocated to this field.

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