Factors affecting the annual abundance and regional distribution of English inshore demersal fish populations: 1973 to 1995

Abstract

The 2 m beam trawl and 1.5 m push net were used to sample the small epibenthic fish assemblage during September on the east and south coasts of England. Fishing stations were distributed along the entire coast within four depth bands to 20 m. A total of 104 species were caught between 1973 and 1995, and these included infrequent Lusitanean species such as the big-scale sand-smelt (Atherina boyeri), and the undulate ray (Raja undulata), and infrequent boreal species such as the Norway haddock (Sebastes viviparus). Fifty-four taxa were selected as representative of the small, demersal inshore fish community that would be most vulnerable to capture by the two sampling gears, and were used in subsequent analyses of community structure. The north-east coast assemblage was the least diverse (H*=1.58) and least even (J*=0.47). It also supported the least number of species (55), and the variation in catch of the only dominant genus, Pomatoschistus spp., was partly responsible for large year-to-year variations in diversity and in the total population abundance of selected demersal species. On the east and south-east coasts, both diversity (H*=1.78 and 1.93) and evenness (J*=0.50 and 0.51) were greater than in the north, as a result of larger numbers of species available to the gears, and several species with relatively high catch density, such as Pomatoschistus spp., dab (Limanda limanda), solenette (Buglossidium luteum), and dragonet (Callionymidae). As a result, thefish assemblages of these coasts showed lower inter-annual variation in evenness and diversity. Trends in mean catch density of some species were correlated with the mean surface water temperature and salinity, especially for species which were near the edge of their normal geographic distribution in the southern North Sea. In addition, mean surface water temperatures were positively correlated with the total number of Lusitanean species on the south coast. These data provide evidence that during a period of more than 20 years, hydrographic factors have not only aVected species abundance, but, at low density, also their presence or absence in catches. ? 1996 International Council for the Exploration of the Sea