Powan,Coregonus lavaretus(L.), ova predation by newly introduced ruffe,Gymnocephalus cernuus(L.), in Loch Lomond, Scotland

摘要

Abstract.Loch Lomond, one of the few British strongholds of the powan,Coregonus lavaretus(L.), has recently been colonized by the ruffe,Gymnocephalus cernuus(L.). The ruffe are now widespread, abundant and one of the commonest fish in Loch Lomond. Analysis of the gut contents of these fish caught on powan spawning grounds in Loch Lomond showed that they, as well as native brown trout,Salmo truttaL., and powan themselves, prey upon powan ova. Ruffe maintained a high winter feeding rate compared with powan and trout and fed on a broad range of benthic prey, of which powan ova formed the greatest biomass (84 of total diet) and dominated the diet numerically (57 of prey items). The observed incidence of powan ova consumption by ruffe was significantly greater than that of both brown trout and powan (P<0·001)