Low success rate in re-establishing European perch in some highly acidified lakes in southernmost Norway

摘要

In order to test whether major reductions in acid inputs had improved water quality sufficiently for fish populations to recover, we stocked wild European perch (Perca fluviatilis) in there highly acidified lakes that had previously supported this species, and in one limed lake. The fish, which were introduced from a local lake (donor lake), generally ranged from 12 to 16 cm in total length, and were stocked at densities of 117-177 fish ha{sup}(-1). The untreated lakes were highly acid, with minimum pH values and maximum inorganic aluminium concentrations (Al{sub}i) during the spring of 4.6-4.7 and 118-151μg L{sup}(-1) respectively. In the limed lake, the corresponding values for pH and Al{sub}i ranged between 5.8 and 6.6 and 5 and 19μg L{sup}(-1) respectively. Gill-netting in two subsequent years after the introduction yielded only a few recuits (0+) and one adult in one of the there acidified lakes in one year only. However, stocked perch reproduced successfully in both years in the limed lake. There was a significant linear relationship between the catches (CPUE) of juvenile perch (age 0+) in the different lakes in the autumn and the water quality in May (time of hatching), both in terms of Al{sub}i (r{sup}2 = 0.934, P<0.05) and pH (r{sup}2 = 0.939, P<0.05). Our data suggest unsuccessful recruitment in waters of pH <5.1 and Al{sub}i> 60μg L{sup}(-1).