Effects of fish density and size on survival, growth and production of hatchery-reared brown trout ( Salmo trutta L.) in lakes

Abstract

Four small lakes (0.9–7.5 ha) were each stocked with 500 individually tagged, 1-year-old hatcheryreared brown trout ( Salmo trutta), corresponding to densities of between 67 and 250 fish ha −1. The lakes were treated with rotenone 1 year before stocking to eliminate pike ( Esox lucius). Population estimates were carried out 14 months after stocking by the removal method, using a series of standard gill nets during two successive nights. No recaptures were obtained in a lake which still harboured adult pike. Population estimates in the three lakes ranged from 101 to 249 specimens, corresponding to survival rates of 0.2–0.5. The survival rates were positively related to initial stocking density. Both recapture rate and length at recapture were significantly correlated with initial fish length. Mean length at recapture as well as back-calculated length at the age of 2 years exhibited a negative relationship to fish density at the end of the study period. The greatest production (30.88 kg ha −1) was obtained in the lake stocked at the highest rate (250 fish ha −1). A higher growth rate in the lake with less fish could only partially compensate for slower growth in the more densely populated lakes. Hence, production in the lakes was limited by factors affecting survival.