Effects of Climatic and Density-Dependent Factors on Year-Class Strength of Coregonus lavaretus in Lake Constance

Abstract

The influences of density-dependent and density-independent factors on year-class strength (YCS) of Coregonus lavaretus in Lake Constance were studied by multiple linear regression analyses for the period from 1962 to 1982. Meteorological conditions that lead to early thermal stratification of the lake in April are of prime importance for YCS and account for 41% of the total YCS variance. Zooplankton concentration during spring has no significant influence on YCS. The extensive stocking program on the lake (50–200 million larvae stocked per year) significantly supports YCS, but this relationship becomes apparent only after the influence of meteorological conditions are removed from the data. Conspecifics of age-classes 1 and 2 have a negative influence on the age 0 year-class, but the nature of this intraspecific competition remains unknown. No stock–recruitment relationship could be detected in this study. The final model includes five independent variables and accounts for 84% of the total YCS variance.