The structure of North Sea benthic invertebrate and fish communities is an important indicator of anthropogenic and environmental impacts. Although North Sea fish stocks are monitored regularly, benthic fauna are not. Here, we report the results of a survey carried out in 2000, in which five nations sampled the epibenthic and fish fauna at 270 stations throughout the North Sea. The aim of the survey was to investigate the diversity and community structure of epibenthic and fish communities and to identify relationships with environmental factors, including the frequency of commercial otter and beam trawling disturbance. Epibenthic species diversity was lower in the southern North Sea than in central and northern areas. Fish, conversely, were more diverse in the south. The 50 m, 100 m and 200 m depth contours broadly defined the boundaries of benthic and fish communities. The abundance of epibenthos of the southern North Sea was dominated by free-living species, whilst north of the 50 m contour sessile species prevailed. A hybrid area, with sessile species typical of the north and free-living species characteristic of the south, was found off the Norfolk and Flamborough coast stretching towards the Dogger Bank. Large-scale hydrodynamic phenomena were most likely to be responsible for the main divisions between communities, especially the boundary between mixed and stratified water masses. However, bottom temperature, sediment parameters and beam trawling were closely correlated with species richness and diversity, as well as community patterns, and may modify regional species composition. Our study shows that effective large-scale sampling of benthic communities can be conducted during existing fisheries surveys. Since annual fisheries surveys are conducted throughout the northeast Atlantic shelf seas, concurrent benthic surveys would allow benthic sampling on unprecedented spatial and temporal scales. The samples would help to monitor the environmental impacts of trawling disturbance, climate change, pollution and other natural and anthropogenic factors

The assemblages of attached and freeliving epibenthic species in the North Sea are described, based on analysis of samples collected with a small beam trawl. Clustering of survey sites based on the presence or absence of attached species indicated that three regions had characteristic assemblages: the northern North Sea, the central North Sea from 55 to 57°N and the southern North Sea. Clustering of sites based on counts of free-living epibenthic species also revealed that the sites formed three major groups but these corresponded to regions in the north-east North Sea, the northern and western central North Sea and the southern and eastern central North Sea. Species which contributed most to the similarity within and dissimilarity between groups were identified. The environmental factors which best accounted for the grouping of sites were depth, winter temperature and the temperature difference between winter and summer for attached species and depth and the temperature difference between winter and summer for free-living species. The species richness of attached and free-living epibenthic species was higher in the central and northern North Sea than in the south. The number of abundant (Hill's N1) and very abundant (Hill's N2) free-living species also increased from south to north.

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-Fisheries research monitoring surveys provide an ensemble of measurements on fish stocks and their environment. Because the interannual variability in such survey-based indicators is high and because diagnostics on fish stocks cannot be based on noise, our concern is to make use of what is continuous in time to obtain a reliable diagnostic. In this paper, we show how min/max autocorrelation factors (MAFs) can be useful for assessing the status of a fish stock. Indeed, MAFs will allow us to (i) summarize the multivariate indicator signals into orthogonal factors that are continuous in time, (ii) select those indicators that carry the major signal in time, and (iii) forecast stock status by modelling the time continuity of the MAFs. These different potential uses of MAFs in an indicator-based approach to assessment were illustrated with North Sea cod, for which a suite of biological and spatial indicators are available over a 21-year survey series.

In 1999 the epibenthic fauna of the North Sea was investigated using the 3rd quarter 'International Bottom Trawl Survey' of five European countries. Altogether 241 stations were sampled covering 143 ICES rectangles. The objectives of the projects were (i) to analyse epibenthic diversity patterns in the North Sea, (ii) to identify the spatial distribution of faunal communities and (iii) to relate environmental factors as well as fishing effort to species diversity. Epibenthic fauna was clearly divided between the southern North Sea and the central-northern North Sea, roughly along the 50 m depth line. The separation was based on an overall higher number of species in the central and northern North Sea and a change in the species composition from north to south. Sessile fauna including erect, branching species like bryozoans and hydrozoans were particularly diverse along a corridor in the central-northern North Sea between 56° and 58°N, coinciding with the area between the 50 m and 100 m depth line. Cluster analysis, based on the structure of the community, confirmed the north-south gradient found for species diversity. Separation of clusters was driven to a great extent by species occurring predominantly or exclusively north of the 50 m contour line. Few species were exclusive to the south, but a number of scavenging species were found here more frequently and in higher numbers. Depth was positively correlated with the diversity of free-living fauna, whereas the type of sediment showed no significant relationship with variations in numbers of species. Beam-trawling effort was negatively correlated with the diversity of sessile fauna