Spatial patterns of whiting abundance in Scottish waters and relationships with environmental variables

This paper uses objective classification methods, a combination of principal components analysis (PCA) and cluster analysis, applied to long-term average data, to define areas of similar seasonal patterns of whiting abundance in Scottish waters, based on fishery data on landings and effort (by month and by ICES rectangle). A geographic information system (GIS) is used to qualitatively describe the relationships of these spatial patterns of whiting abundance with (a) trawl survey catch rates by age-class, and (b) environmental factors. The results show that the spatial patterns of whiting abundance are related to age, as well as to depth and to spatial patterns of sea surface temperature (SST) in winter. The area (within the North Sea) of highest whiting abundance, and the largest seasonal change in whiting abundance, corresponds to the area of highest survey catch rates for older (>2 years old) whiting in winter, a particular spatial pattern of SST in winter and water depths of 100–200 m. This spatial pattern of SST may indicate an effect of the inflow of the North Atlantic water. This study provides a guide for selecting study areas for future quantitative analysis and the methods proposed may also provide a useful management tool.