Annual and diel activity cycles of a northern population of the large migratory cyprinid fish asp ( Leuciscus aspius )

Little is known about the exact movement parameters of migratory cyprinids listed as conservation priorities. A northern population of predatory asp, listed on the Bern Convention Appendix III, was studied in a near natural lake–river ecosystem by tracking adult fish tagged with acoustic transmitters for 32 months. Activity levels in terms of swimming speed, swimming distance and movement range were four times higher during the warmer part of the year (water temperatures > 12–15 °C, April/May–September), which coincides with their main feeding period, than other times of the year. All fish had an annual riverine movement range larger than 40 km (max 110 km). Asp activity was affected by light, habitat type and water discharge. For most of the year, activity levels, in terms of number of movements per time unit, were higher during dawn and dusk than during day and night. Under poor light conditions and low temperatures, activity was also relatively high during the day. Fish were more likely to swim upstream around sunrise or during the day than during other diel periods. Knowledge about high-activity periods, which may render the fish vulnerable to fishing and other impacts, can be used to develop and evaluate fishing regulations. Large annual movement ranges highlight the need for extensive continuous river systems open for migration between essential habitats. This study emphasises the need for region-specific research on the ecology and behaviour of fish populations in order to facilitate protection of the populations in the face of negative human impacts.