Re-establishment of perch in three lakes recovering from acidification : rapid growth associated with abundant food resources

In 2002, we reintroduced perch (Perca fluviatilis) into three small, previously heavily acidified and fishless lakes. Test fishing indicated that released perch had survived in all three study lakes and reproduced successfully in two of them. Growth of introduced individuals had increased sharply after introduction. The increased growth of perch was an apparent consequence of high abundance of macroinvertebrates in the fishless lakes. Activity traps indicated even a 90% decrease in the numbers and size of invertebrates upon the fish releases: a very likely response to the predation by the stocked perch. Our observations indicate that the chemical recovery of the study lakes from acidification has been remarkable enough to allow recolonization by aquatic organisms. For perch, and probably for other acid tolerant fish, this means the possibility of a successful re-establishment of populations in previously acidified fishless lakes which, in turn, increases the value of such lakes for fishing.