Using the delta C-13 and delta N-15 of whitefish scales for retrospective ecological studies: changes in isotope signatures during the restoration of Lake Geneva, 1980-2001

The scales of whitefish Coregonus lavaretus were used in place of dorsal muscle, which necessitates killing the fish, to study food webs from the delta(13)C and delta(15)N isotopic ratios in the organic fraction. As scales are composed of both organic and calcified fractions, a protocol for scale decalcification was first devised. The delta(13)C and delta(15)N values of the decalcified scales were then shown to be closely correlated to those of the dorsal muscle, demonstrating that scales could be used in place of muscle to study food webs. Changes in the delta(13)C of whitefish were determined from a scale collection that extended over the period during which the trophic state of Lake Geneva was recovering. (C) 2003 The Fisheries Society of the British Isles.