Validation of a numerical model for the study of anchovy recruitment in the Bay of Biscay

Some responses of the sea to the forcing agents actuating on it can be represented as differential equations in partial derivatives. Equations most frequently used to describe sea currents are the shallow water equations (SWE). These SWE are derived from the equations for the conservation of momentum and continuity making the assumptions that the pressure distribution is hydrostatic and that the terms referring to the vertical velocity are negligible. Unfortunately, the analytical resolution of the SWE is impossible and requires of the use of numerical approximation algorithms. The method used for the calculation of currents induced by the wind and by the astronomical tide in the area of the Bay of Biscay is the quasi-3D approximation using finite elements. Anchovy is a species of high economic interest for the Basque Country's fleet. Eggs and larvae of this species behave as passive particles and are drifted around close to the surface (first 50 m) by sea currents. The behaviour of these particles can be represented by means of the general convection/diffusion equation, and by adding a source-decay term, the mortality of larvae can be represented. The Taylor-Galerkin technique adequate for problems in which convection dominates, allows the application of the finite element method to solve the dispersion in the marine environment. In this paper the preliminary results are presented concerning the numerical simulation of the drifting process of anchovy eggs and larvae from spawning areas, towards areas where they are fished. Results will be compared with survey data.