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The addition of heavy, spiked, linked tickler chains (chain mat) to a 2 m beam trawl without chain mat increased the catch rates of some epibenthic species, but not others. Catch rates of the invertebrates Asten'as rubens, Ophiura ophiura, Liocarcinus holsatus and all combined flatfish species increased. In contrast, the catch rates of the epibenthic teleosts Callionymus spp. decreased, but those of Echiichthys vipera were not affected. Comparisons with data in other studies suggested that this modification increased the catch rates of epifauna to give an improved estimate of population density. Although total biomass of the catch increased with tow durations between 2.5 and 7.5 min, there was no significant effect on estimates of either standardised species abundance or biomass ha-' Although short tows reduce catch sorting time, the variation between samples was greater than for longer tows (7.5 min). Hence, it is suggested that the latter are preferable for estimating population density and community structure, although this may depend on the spatial dimensions and objectives of the study. The results are discussed in the context of the use of the gear as a sampling tool in ecological surveys of epibenthic communities In sublittoral and coastal shelf areas.

Improving quantitative surveys of epibenthic communities using a modified 2 m beam trawl