Analysis of cod, haddock and whiting distribution in UK waters in relation to environmental variables
This study systematically analysed the spatial distribution of cod (Gadus morhua, [Linnaeus, 1758]), haddock (Melanogrammus aeglefinus, [Linnaeus, 1758]) and whiting (Merlangius merlangus, [Linnaeus, 1758]) in UK waters, with particular reference to the North Sea and west coast of Scotland, in relation to environmental variables: sea surface temperature (SST), sea bottom temperature (SBT) and depth using a combination of qualitative (geographic information systems) and quantitative (statistics) methods. Fish abundance data were derived from both survey and fisheries records. The analysis showed: 1. There is a great heterogeneity in spatial and temporal (seasonal) distribution of whiting. The spatial distribution of whiting in winter is related to age, as well as to depth and to spatial patterns of SST at the same time. The area (within the northern North Sea) of highest whiting abundance (derived from fishery data), and the largest seasonal change in the abundance, corresponds to the area of highest survey catch rates for older (>2 years) whiting in winter, a particular spatial pattern of SST in winter and water depths of 100-200 m. 2. Generalised additive models (GAMs) fitted to whiting abundance (derived from fishery data) in the northern North Sea in relation to SST, SBT and depth showed marked seasonal changes in the spatial relationships between whiting abundance and these environmental variables. In the northern North Sea, SST apparently has important influence on the spatial distribution of whiting, especially during winter and spring (from December to April): where the water is relatively warm (reflected in SST), whiting abundance is relatively high. In summer, this relationship disappears. The inter-annual changes in the strength of the warmness in winter and spring seem to have effect on the inter-annual changes of whiting abundance at 0-2 years lag time. The relatively warm areas in winter and spring in the northern North Sea result partially from the Atlantic current. SST acts as an indicator of the effect of Atlantic currents on local waters.