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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