Knowledge of movement patterns is essential for the effective conservation of noble crayfish (Astacus astacus) and stone crayfish (Austropotamobius torrentium), two endangered species indigenous to Central Europe. Radiotelemetry was used to evaluate diel changes in ranging behaviour and local activity of both species at a locality where they occur sympatrically. Both species exhibited similar behaviour, migrating mostly in the upstream direction. Movement probability differed significantly within both species between phases of the diel cycle. Movement probability within 3-h tracking intervals was highest at dawn (18.18 %) and night (15.32 %) in A. astacus, and at dawn (37.25 %) in A. torrentium. Astacus astacus moved the longest distances during the dawn interval (3.70 m) and the shortest during the day (1.41 m) and night (1.61 m) interval. The distances moved by A. torrentium did not differ significantly in different phases of the diel cycle. Local activity was highest at dusk in A. astacus (40.6 % likelihood of activity) and during dusk and night hours in A. torrentium (30.8 % and 24.2 % likelihood of activity). Body size and environmental parameters (light intensity, weather, atmospheric pressure, water temperature and turbidity) also influenced crayfish behaviour. Both species exhibited a post-handling fright response, which (e.g. in mark-recapture studies) can lead to the overestimation of movement rates and the extent of natural migrations.
This article reports on the results of the first radiotelemetric field study comparing the movement patterns of juvenile and adult noble crayfish (Astacus astacus) over the 24-h cycle. During our study (in summer, outside the reproduction period), juveniles moved over significantly longer distances than adults; upstream movements prevailed in both groups. The longest distance covered by an individual crayfish during a three-hour interval was 110 m (in the upstream direction). Adults moved most frequently at dusk and least frequently during daytime. Among juveniles, the likelihood of movement did not significantly differ between the times of day; however, distances covered by juveniles were the longest at night and significantly shorter during daytime and at dusk. Juveniles and adults exhibited very similar local activity (motion within a single place) with high values at night and low values during daytime.
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