Fishing or the environment - what regulates recruitment of an exploited marginal vendace (Coregonus albula (L.)) population?

Fish populations inhabiting marginal areas are generally highly susceptible to environmental variation and therefore show large fluctuations in recruitment. The commercially important, and usually freshwater, vendace (Coregonus albula (L.)) occupying the brackish waters of the Bothnian Bay forms one such marginal population and shows large annual variation in recruitment. Here, we investigate the relative importance of fishing (trawling time), hydro-climatic factors and species interactions in explaining the variability in vendace recruitment using three sets of models. A comparison of the best models in the hydro-climatic model set and the fishing model revealed that the hydro-climatic variables were overall superior to the anthropogenic model in describing recruitment variability. Trawling time and water temperature in winter combined with salinity explained 33 and 63.7% of the variation in recruitment, respectively. The importance of water temperature and salinity, in combination with the effects of trawling time, calls for catch levels to be set with caution in this vendace fishery.