Spatial synchrony in the inter-annual population variation of vendace (Coregonus albula (L.)) in Finnish lakes

We analysed the spatial scale of synchrony in the inter-annual variation of vendace population indices from time-series of 21 Finnish lake basins. We detected significant positive correlation between lakes in the variation of abundance of young-of-the-year recruits, residuals of a density dependence model for recruitment, newly hatched larvae and spawning stocks. The spatial scale of correlation was typically 100-300 km and anisotropic, being shorter along the north-south vector of distance than along the east-west vector. The outcomes did not change when the data were restricted to rule out cases with a possibility of dispersal between populations. The scale and anisotropy structure of synchrony in mean temperature during the four week period after the local ice break date closely resembled that of the vendace population indices. Regionally correlated exogenous factors synchronise the recruitment variation either directly or perhaps also through environmentally induced synchrony in predator stocks. The effective scale of correlation for these factors, especially along the north-south axis, can be short if a large proportion of the prerecruit mortality occurs during a short period and the timing of this period at different latitudes varies by weeks due to differences in time of ice break and vendace hatching.