A three dimensional, full life cycle, anchovy and sardine model for the North Aegean Sea (Eastern Mediterranean): Validation, sensitivity and climatic scenario simulations

Abstract

We present the development of a 3D full-lifecycle, individual-based model (IBM) for anchovy and sardine, online coupled with an existing hydrodynamic/biogeochemical low-trophic level (LTL) model for the North Aegean Sea. This IBM was built on an existing 1D model for the same species and area, with the addition of a horizontal movement scheme. In the model, both species evolve from the embryonic stage (egg+yolk sac larva) to the larval, juvenile, and adult stages. Somatic growth is simulated with the use of a “Wisconsin” type bioenergetics model and fish populations are computed considering reproduction and mortality (natural, fishing, starvation), along with an adaptation of the ‘super individuals’ (SI) approach. The 2000-2010 period was selected for the reference simulation and model calibration, in terms of fish growth and population biomass. The interannual biomass variability of anchovy was successfully represented by the model, while the simulated biomass of sardine exhibited low variability and did not satisfactorily reproduce the interannual variability observed in acoustic surveys. The spatial biomass distribution of both species was in relatively good agreement with field data. Additional single-species simulations revealed that species compete for food resources. Temperature sensitivity experiments showed that both species reacted negatively to a temperature increase. Anchovy, in particular, was more affected since its spawning and larval growth periods largely overlap with the period of maximum yearly temperature and low prey concentration. Finally, simulation experiments using IPCC climatic scenarios showed that the predicted temperature increase, and zooplankton concentration decrease will negatively affect anchovy, resulting in sardine prevalence.