The influence of oceanographic conditions and larval behaviour on settlement success—the European sea bass Dicentrarchus labrax (L.)

The European Seabass (Dicentrarchus labrax) is a slow-growing late maturing fish. The northern stock has been declining since 2010 and is thought to be caused by a combination of fishing and weak year classes. Large inter-annual variation in settlement has been observed, so a better understanding of the mechanisms driving settlement success will aid interpretation of the variation between years, and help to improve the stock assessment models and management strategies. In this study, an individual-based model (IBM) was developed to investigate the factors affecting sea bass settlement on nursery grounds of the northern sea bass stock. The IBM was coupled with hydrodynamics to track particles, whereas egg and larval development, and vertical migration behaviour are fully incorporated. The IBM successfully predicted inter-annual differences in settlement regardless of larval behaviour. The highest settlement success was predicted with neutrally buoyant eggs, hatchlings, and larval stages, in combination with tidal migration at the final larval stage. Dispersal was driven mainly by the influence of wind on residual currents and water temperature, with warmer temperatures reducing the duration of the pelagic phase and stronger current increasing the potential to drift further. Eggs spawned in the central western English Channel settled in both England and France, with movement from the central to the eastern English Channel occurring only in warm years. Larval duration was driven by water temperature and showed an increase in duration from the southwest to northeast areas of the northern stock. The results are discussed in the context of sea bass management and conservation strategies.