TROPHIC POLYMORPHISM AMONGST ARCTIC CHARR FROM LOCH-RANNOCH, SCOTLAND

This paper describes the results of a multivariate and univariate morp hometric analysis of three groups of Arctic charr Salvelinus alpinus f rom Loch Rannoch, Perthshire, Scotland, distinguished a priori on the basis of coloration (bright v. cryptic) and site of capture (From two locations 12 km apart). The analysis produced a clear and highly signi ficant distinction, not only between brightly and cryptically coloured charr, but also between the two cryptically coloured groups, one of w hich was more robust in terms of several size-independent head measure ments. Stomach analysis showed that the brightly coloured charr fed en tirely on zooplankton, the less robust, cryptically coloured fish, fed on benthic macroinvertebrates, whereas a significant proportion of th e diet of the more robust cryptically-coloured form consisted of other fish. Differences in length at age also distinguished the three forms , with the robust, piscivorous charr, which live longer and potentiall y reach a larger final size, attaining smaller sizes at a given age. T hese data clearly confirm the previous identification of a distinct pl anktivorous morph of Arctic charr in Loch Rannoch and extend the morph analysis by distinguishing two additional morphs, a benthivorous morp h and a piscivorous morph that are morphologically and ecologically di stinct. The results are discussed in the context of other systems in w hich sympatric morphs of Arctic charr have been described. (C) 1998 Th e Fisheries Society of the British Isles.