Fishing effects in northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. VI. Gale effects on vertical distribution and structure of a fish assemblage in the North Sea

The short-term effects of a gale on diversity and assemblage patterns of groundfish in a defined area in the German Eight were analysed using univariate and multivariate statistical techniques. After a gale of considerable strength, the catch rates of some groundfish species exhibited significant daily changes. Catches of the flatfishes dab (Limanda limanda), solenette (Buglossidium luteum), plaice (Pleuronectes platessa) and sole (Solea vulgaris) changed markedly between the first and the second day after the gale. In general, catches of flatfishes were significantly higher on the first day after the gale than before or after, whereas catches of the pelagic species scad (Trachurus trachurus) and mackerel (Scomber scombrus) were significantly higher on the second day after the gale. The detection of these changes in the species assemblage was supported by shifts in diversity indices and multivariate description of community structure (cluster analysis, MDS and SIMPER analysis). The observed differences could be explained by species-specific reactions to higher turbidity and bottom oscillation currents during increased wave-action in shallower waters. The results have important implications for those concerned with the analysis and interpretation of fish abundance data collected during groundfish surveys. (C) 1999 Elsevier Science B.V. All rights reserved.