Fishing effects in northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. III. International trawling effort in the North Sea: an analysis of spatial and temporal trends

This paper describes trends in beam and otter trawling effort in the North Sea from 1977 to 1995. Data are presented as total hours fishing by English, German, Norwegian, Scottish and Welsh vessels for the period 1977–1995, and by Danish, Dutch, English, German, Norwegian, Scottish and Welsh vessels for the period 1990–1995. Analyses of temporal trends indicated that total international trawling effort in the entire North Sea has increased slowly since 1977 and that it is currently (1995) 2.25 million h yr⁻¹ of which 55% is due to beam trawling. Spatial analyses indicate that the proportion of beam trawling effort increases from north to south. Plots of annual fishing effort by ICES statistical rectangle (211 boxes of 0.5° latitude×1° longitude) indicate that the majority of fishing effort in the North Sea are concentrated in a very few rectangles. Thus mean annual total fishing effort (1990–1995) was less than 2 000 h in 29% of rectangles and less than 10 000 h in 66% of rectangles. Total effort exceeded 40 000 h in 4% of rectangles. The results indicate that assessments of the average area swept by trawls in the North Sea give a poor indication of the direct impacts of trawling on the biota. Some areas are intensively fished but many others are not. Our dataset is likely to underestimate trawling effort in the southern North Sea (ICES Area IVc) because data for Belgian and French vessels were not available. However, the absence of French and Belgian data would not significantly alter total trawling effort estimates from the central (IVb) and northern (IVa) North Sea.