Do goldeneye and perch compete for food?

We tested Eriksson's (1979) hypothesis that goldeneye and perch compete for invertebrate prey. (1) Diet overlap was high on both prey type (71%) and prey size (80%). Ephemeroptera nymphs and Trichoptera larvae made up over 65% of the stomach contents of goldeneye and perch, and over 80% of the diets of both species were organisms in the 0-20 mm size range. (2) Goldeneye and perch co-occurred on all three study lakes but there was an inverse relationship between their abundances on nine study plots within those lakes. This reciprocal density trend was not due merely to differences in habitat use by perch and goldeneye. When variation in habitat structure was controlled via partial correlation techniques, the reciprocal density trend remained. (3) An alternative hypothesis that density dependent predation maintained habitat separation of perch and goldeneye was not supported. (4) Food resources were limited in at least some sites. (5) Sites which supported populations of both perch and goldeneye had a significantly greater diversity of resources and a tendency toward higher levels of food production than sites in which only one or neither species occurred. (6) We cannot reject Eriksson's (1979) hypothesis. Our results are in agreement with his studies in Sweden and suggest that interactions between goldeneye and Perca spp. may be comparable over large geographic areas.