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RESEARCH PRODUCT

Use of stable isotope analysis to evaluate the possible impact of fish migration on a lake biomanipulation

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1. A lake restoration project involving mass fish removals was started to improve further the water quality of a lake recovering from severe eutrophication. The effectiveness of such biomanipulation as a lake management option could be compromised if removed fish are rapidly replaced by large-scale immigration from a connected lake. 2. Stable isotope analysis (SIA) was used to examine the migrations of perch (Perca fluviatilis L.) and roach (Rutilus rutilus (L.)) between two connected lakes in central Finland, Jyvasjarvi and the larger Paijanne. Baseline δ15N signatures in primary consumers were significantly higher in Jyvasjarvi and this difference was reflected further up the food chain in fish. 3. Spring fish spawning migrations from Paijanne resulted in a significant decrease in mean δ15N signatures of both perch and roach in the adjacent part of Jyvasjarvi, but by summer these mean δ15N signatures in fish muscle tissue had increased again to match those in the rest of the lake. δ13C signatures of both fish species were more variable and were of less value for tracking fish migrations. 4. A robust discriminant analysis was used to classify perch and roach caught from Jyvasjarvi into fish originating from either Jyvasjarvi or Paijanne. The greatest proportions of immigrant perch and roach in Jyvasjarvi were observed in spring 2004 (71% and 56%), when biomanipulation of Jyvasjarvi had started. Immigrant fish percentages in the following spring were considerably lower (24% and 14%, respectively), most likely dueto effective biomanipulation. 5. Results indicate that the current biomanipulation has decreased the extent of the spring migration, and that immigrant fish have not significantly repopulated Jyvasjarvi after the intense fishing. More generally, the data illustrate how stable isotopes offer the possibility to track migrations of common fish species between adjacent freshwater lakes. Copyright © 2007 John Wiley & Sons, Ltd.