Results of whitefish,Coregonus lavaretusL., fingerling stocking in the lower part of the Sotkamo water course, northern Finland

摘要

Abstract.The efficiency of stocking with whitefish,Coregonus lavaretusL., fingerlings was assessed in a large lake system with a naturally reproducing local whitefish stock. After the start of the stocking programme, the whitetish catch increased. The proportion of stocked whitefish in the catch was ca. 50. The calculated yield per thousand released fingerlings was 57 ± 18kg. Further, the efficiency of stocking may be indicated by the following facts. Prior to stocking, the whitefish catch decreased, evidently due to recruitment overfishing. It was suggested that this situation was corrected by stocking with fingerlings and the whitefish catch then increased. The catch per unit of effort (CPUE) generally decreases with increasing fishing effort, but in this case the CPUE remained at the same level in spite of a considerable increase in fishing effort. The growth rate depends on the density of the fish stock. In this case the growth rate declined, possibly due to the fact that fingerling stocking increased the population density