Environmentally caused variability in the fluctuations of the European lobster, Homarus gammarus, fishery in Scottish coasts

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Variability in the fluctuations of two Scottish lobster populations, the Hebrides and Southeast, was investigated from available long data series of fishery and environmental variables. In a multivariate context, relationships between selected environmental variables and the fishery data were studied at different spatial and temporal (annual, spring and autumn) scales and from individual and overall sampled fleet. Multivariate techniques such as cross correlation function (CCF), principal components analysis (PCA) and redundancy analysis (RDA) confirmed that the capture of lobsters was strongly influenced by sea surface temperature (SST), wind speed (WS), and sea level pressure (SLP) throughout the year, and this dependence affected the duration of the fishery. In the Hebrides, the total variation (42%) of the interaction fishery-environmental variables for the spring and autumn fisheries could be attributed to the environmental variables in an 89%. For the Southeast, the spring fishery was more affected by changes in the environment, with a total variation of 34%, from which 85% could be explained by the environmental variables tested, than the autumn fishery where density-dependent processes were more important. From the analyses, it is deduced that the Hebrides lobster population is strongly influenced by densityindependence processes at large and small spatial scales. Density-dependent processes at all spatial scales mainly drive the Southeast lobster population and environmental variables are important in spring.