The distribution and movements of intertidal butterfish Pholisgunnellus were studied on the westcoast of Scotland in relation to the foraging tactics of one of its major predators, the otter. Fish were individually tagged and released at low tide in restricted areas of 5 m wide running from the top of the shore towards the sea. Population density increased from 015 fish m" at the top of the shore to 1–1 fish nv in the Laminaria zone. The median total length of all fish examined was 92 mm (N=369) with a very distinct length class of 70–80 mm. There was no relationship between length and position on the shore. Only 24 out of 156 tagged fish were recaptured inside the restricted areas. The recaptured fish had moved a mean of 21 m (SD 1–9 m) in 1–6 days (SD 1–0 days), the directions of movement being randomly distributed. Repopulation rates were studied by removing all fish from three areas of approximately 180 m each. Fish of the same size moved into the cleared areas within two tidal cycles although in much smaller numbers (only 27–52% of the initial populations). Disturbance of the habitat probably played an important role because there was a general decline in numbers in regularly visited areas throughout the experiments. It is concluded that, even allowing for this disturbance intertidal butterfish are mobile and relatively unrestricted in their movements. From the point of view of predators like the otter and the heron, more butterfish are to be caught lower down the shore and each butterfish caught will soon be replaced by another of about the same size.