Trophic polymorphism among Arctic charr Salvelinus alpinus L., from Loch Ericht, Scotland

This article examines the morphology and ecology of Arctic charr Salvelinus alpinus in Loch Ericht, Scotland. Gill netting revealed that two forms of charr existed within the loch, a pale form and a colored form. Multivariate analysis of nine size-corrected morphometric measurements of the head regi on revealed that pale and colored charr differed significantly in the size and shape of the head characteristics and that both groups were easily disc riminated on the basis of these characteristics. Stomach contents showed th at the colored form fed predominantly on zooplankton and the pale form main ly consumed benthic macro-invertebrates, with larger pale individuals consu ming other fish. On the basis of diet and morphology, the terms planktivoro us and piscivorous were adopted for the two forms respectively. Length at a ge also distinguished the two groups, with piscivorous charr being smaller than colored charr up to age 8+ then surpassing the maximum length attained by planktivorous charr at ages of 9+ and above. The results are discussed in relation to other instances of sympatric morphs of Arctic charr.