Characteristics of anadromous whitefish (Coregonus lavaretus (L.)) rivers in the Gulf of Bothnia.

In order to study anadromous whitefish spawning river requirements, we sampled 41 rivers in the Gulf of Bothnia for newly hatched whitefish larvae for one to three consecutive years. Chemical and morphological data (e. g. flow rate, topography, pH, estuary fetch and distance to coastal sandy areas) were collected for each river. Newly-hatched whitefish were caught in 19 rivers whereas whitefish were not confirmed present in 22 rivers. By applying partial least squares discriminant analysis (PLS-DA), data for rivers confirmed to support whitefish were contrasted with data for rivers in which whitefish were not found. The single most important factor was annual average water flow rate. Whitefish larvae were observed in 93% of the rivers with annual mean flow rate > 5 m3 s-1 (N = 14). In contrast, newlyhatched whitefish were only found in 22% of the smaller rivers (N = 27).