Variability in the spatio-temporal distribution of larval European whitefi sh (Coregonus lavaretus (L.)) in two Austrian lakes

Abstract

The spatial and temporal distributions of larval European whitefish (Coregonus lavaretus, species complex) were investigated in the years 1998 and 1999 in two Austrian lakes, Traunsee and Hallstattersee. The fish communities of both lakes are dominated by whitefish, but in addition to a normal-growing form Traunsee is also inhabited by a dwarf phenotype. Larval sampling was done weekly between January and June using a push net system. Whitefish larvae showed a preference for nearshore areas at both lakes. In Traunsee, the mean catch on the first sampling date was higher than those obtained during the following sampling dates in February for both years. A local minimum in temporal occurrence was observed in mid-February (1998) or early February (1999). Catches increased again during March before reaching a maximum in early April of both years. In Hallstattersee, the sampling started at the beginning of February with very few larvae caught. During the subsequent weeks the catches increased steadily until a single peak was reached in mid-March (1998) or late April (1999). This high within-lake variability in maximum larval occurrence between two successive years is the greatest ever reported. The degree of variation in spatial distribution of larvae observed between years was also novel.