Spatio-temporal distribution of vendace (Coregonus albula (L.)) larvae in Finnish lakes

Newly hatched vendace larvae were sampled annually from 1990-2005 from 10-20 sampling sites in 10 Finnish lakes or basins. The larval densities obtained were analyzed to reveal their spatial distribution. Two sequential surveys were performed in order to estimate the temporal stability. Significant correlations of vendace larval densities were found between the first and second surveys of the same year and between the different sampling years. Spatial distribution analysis showed that the squared differences of larval densities between different sampling sites were high and fairly constant at a scale of distances from 2 km and greater from their site origin. Thus, a minimum distances 2 km between sampling sites produces a random sample of independent observations. In contrast, small distances between sampling sites can be utilized by interpolating the areal pattern of density via geostatistical methods. Fixed and random sampling site procedures were compared. Use of fixed sampling sites from year to year produced more accurate within-season mortality estimates and increased detectability of between-year variation in larval vendace density than random sampling.