An automated system for monitoring fish activity patterns

Passive integrated transponder (PIT) tags potentially allow the automated recording of the movements of individual animals. Here we describe a system designed to log the activity patterns of fish that use a discrete refuge when they are not feeding. The system was demonstrated with juvenile salmonids, which in winter seek shelter during the day in crevices under stones in the streambed but emerge to feed at night. The PIT tag antennae monitored a tube connecting a refuge to a standard hatchery tank and recorded each movement of a fish in or out of the refuge. This method allowed the quantification of individual time budgets for a group of fish sharing the same tank. The efficiency of the system was high, but occasionally the direction of movement could only be ascertained by referring to the previous position of the fish. The technique revealed very synchronized movement by Atlantic salmon Salmo salar out of the refuge at dusk and into it at dawn and intermittent brief excursions from the refuge during daylight hours. The system could be adapted for any species that is large enough to be given a PIT tag and that uses a refuge or burrow (e.g., for breeding or predator avoidance).