The use of winter refuges by roach tagged with miniature radio transmitters

Adult roach (Rutilus rutilus) (13-25 cm) from two shallow lakes, one turbid and one with high water transparency, were tagged with surgically implanted miniature radio transmitters and their habitat use was monitored. Repeated tracking series over the course of the year provided information on seasonal changes in behaviour of roach in the two lakes. The results showed that the roach generally used the lakes only as summer habitat, whereas they moved into specific sheltered, restricted areas during winter. This behaviour was most pronounced in the lake with clear water, where roach gathered in large numbers in the stream in- and outlets as well as in other sheltered habitats where they remained rather passively during the 48 h tracking periods. In the turbid lake, many of the tagged roach, were even found in underground channels during the tracking in November. We see this behaviour as a response to low food abundance, decreased food demand and high predation risk, especially from birds. The tracking data from the clear lake showed that some tagged roach undertook swift habitat shifts from one refuge to the other. The traditional perception of the roach as a 'lake fish' with an important structuring role in the lake ecosystem is undoubtedly true, but the present results suggest that roach are able to migrate between different habitat types and will do so if they can profit from this behaviour.