Invasion and Establishment of Freshwater Fish Populations in Scotland - the experience of the past and lessons for the future.
By Colin E. Adams and Peter S. Maitland
Abstract
Of the 42 species of freshwater fish species with established populations in Scotland only 26 could be regarded as native. 21 of these are species with marine affinities that are presumed to haev invaded Scotland following the last glaciation via a marine route with inly a further 5 being obligate freshwater species, presumed to have arrived by natural dispersal. Of the 16 non-native species comprising 38% of the Scottish ichthyofauna, 14 are obligate freshwater species. the proportion of the fauna this is alien contrasts markedly with the freshwater invertebrate fauna where around 1% of species is alien. This difference results mainly from the considerable interest in fish for recreational sporting purposes and indiscriminate introductions of species into Scottish waters. Despite the significant effect of alien fish in the species list, only few have achieved wide dispersal (e.g. grayling) or have established large populations (e.g. ruffe). Some have dispersed only slowly over decades (e.g. bullhead) but several others are now being moved around indiscriminately by anglers (e.g. dace, tench and crap) and are becoming more widespread. The irreversible impact that ruffe has had on the ecology of Loch Lomond shows the dangers of indiscriminate nmovements of fish, the inability of science to predict the outcome of any introduction reinforces the need for clear legislation to control introductions of fish and to subject introductions to an analysis of the costs and benefits.
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