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As part of a long-term study to examine the ecological effects of beam-trawling, we investigated the immediate impact of fishing on the megafaunal component of a benthic community and the extent to which it had recovered 6 months later. A quantitative dredge was used to collect megafaunal samples following a replicated, paired control and treatment design to maximize the chances of detecting any effects due to trawling. There were two different habitats with distinct communities in the experimental area, one with stable sediments and a rich fauna, the other with mobile sediment and a relatively impoverished fauna. Immediately after fishing the composition of the community in the stable sediments was significantly altered. While the abundance of some species decreased (e.g. sea mice Aphrodita aculeata), others apparently increased (e.g. hermit crabs Pagurus bernhardus). Variation between samples from the fished areas was higher than those from the control areas. This suggests that the effects of trawling were not uniform, even though the treatment area was entirely swept at least once. The effects of fishing were not detectable in the mobile sediments. Six months later, seasonal changes had occurred in both communities and the effects of the trawling disturbance were no longer evident.British Crown copyright 1998

Closed circuit underwater television observations showed that, in summer, large numbers of Carcinus maenas performed daytime tidal migrations up and down a small mudflat in the Menai Strait, North Wales. At the observation point, 25 m above mean low water mark of spring tides, numbers of crabs moving upshore on flood tides averaged 84 m -1 of tideline, ranging from 48 to 126 m^1. Most crabs were of 20-50 mm carapace width (1 and 11 groups); none smaller than 15 mm was seen. Peak movements occurred in at least 0.5 m depth of water. Over the high tide period, most crabs were dispersed over the upper half of the mudflat where crab population densities of 1-8-2-5 m ~2 were indicated by diving observations.

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