Spatio-temporal dynamics of growth and survival of Lesser Sandeel early life-stages in the North Sea: Predictions from a coupled individual-based and hydrodynamic–biogeochemical model

Abstract

Accounting for the individual variability and regional variations are important when predicting recruitment in fish species. Spatially explicit descriptions for recruitment in sandeels are necessary and sandeel growth and survival depend locally on zooplankton prey. We investigate the responses of larval and early juvenile Lesser Sandeel (Ammodytes marinus) in the North Sea to local feeding conditions by an adapted version of a generic bioenergetic individual-based model for larval fish describing growth and survival. Prey encounter and physiological processes are described explicitly in the model, which allows analyzing the influence of prey on the growth and survival of sandeel. The model is coupled to a hydrodynamic–biogeochemical model with physical and prey fields and implemented in temporal and three-dimensional spatial settings. Zooplankton biomass simulated by the biogeochemical model is validated by Continuous Plankton Recorder survey time series data. Spatio-temporal dynamics of the sandeel cohorts are simulated by the integrated model framework for the period 2004–2006 and five major area divisions of suitable sandeel habitats in the North Sea. This allows obtaining insight into the influence of temperature variation and zooplankton availability on the growth and survival. To determine areas promising for recruitment, area divisions are compared and optimal time of hatching for higher survival to recruitment due to match–mismatch with prey is determined by comparing different hatching times. The effect of vertical diel migration behavior of sandeel on the model outcomes is also examined. Vertical migration of sandeel results in increased feeding ability and growth and decreased starvation mortality of individuals. Results show that areas of German Bight and Southern Bight with high zooplankton production support high growth of sandeel. Most sandeel survive to settling in the Dogger Bank area that has large retention on average and still productive in zooplankton. Hatching at the optimal time of March/February with matching zooplankton peak concentrations enhances the growth and survival. Growth correlates positively with the observed temperature trend. Survival correlates negatively with temperature and prominently, when the hatching is in winter.