Stable isotope signatures reveal small-scale spatial separation in populations of European sea bass

摘要

Scientific information about European sea bass Dicentrarchus labrax stocks in the NE Atlantic is limited and a more accurate definition of the stock boundaries in the area is required to improve assessment and management advice. We investigated the connectivity and movement patterns of D. labrax in Wales (UK) using the stable isotope (delta C-13 and delta N-15) composition of their scales. Analysis of delta C-13 and delta N-15 values in the last growing season was performed on 189 adult sea bass caught at 9 coastal feeding grounds. Fish > 50 cm total length (TL) caught in estuaries had very low delta C-13, which is characteristic of freshwater (organic/soil) input, indicating the primary use of estuaries as feeding areas. A random forest classification model was used to test for any differences in delta N-15 and delta C-13 values between north, mid and south Wales and whether it was possible to correctly assign a fish to the area where it was caught. This analysis was restricted to fish of a similar size (40-50 cm TL) caught in open coastal areas (n = 156). The classification model showed that about 75% of the fish could be correctly assigned to their collection region based on their isotope composition. The majority of the misclassifications of fish were of fish from north Wales classifying to mid Wales and vice versa, while the majority of fish from south Wales were correctly assigned (80%). Our findings suggest that 2 sub-populations of sea bass in Welsh waters use separate feeding grounds (south vs. midorth Wales), and may need separate management.