MEPS 546:213-223 (2016)  -  DOI: https://doi.org/10.3354/meps11636

ABSTRACT: 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 (δ¹³C and δ¹⁵N) composition of their scales. Analysis of δ¹³C and δ¹⁵N 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 δ¹³C, 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 δ¹⁵N and δ¹³C 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. mid/north Wales), and may need separate management.

KEY WORDS: Dicentrarchus labrax · Stable isotopes · Random forest classification model · Feeding ground · Stock boundaries