A stable isotope analysis of trophic polymorphism among Arctic charr from Loch Ericht, Scotland

Analysis of nitrogen stable isotope ratios (delta(15)N) in white muscle and liver shows temporal stability in the trophic levels at which the two sympatric morphs of Arctic charr Salvelinus alpinus from Loch Ericht feed. The results confirm an ontogenetic dietary switch to a more piscivorous diet, occurred in all individuals of one of the morphs, above a size threshold of 16.5 cm fork length, indicating that this Occurs at a high frequency in this population and that once made, the return to feeding to a lower trophic level is infrequent. (C) 2004 The Fisheries Society of the British Isles.