Modelling sardine and anchovy ichthyoplankton transport in the Canary Current System

The Canary Current System, centred along the north-western coast of Africa, is one of the four major eastern boundary currents of the world ocean. It sustains a large amount of small pelagic fish, mainly sardine (Sardina pilchardus; Sardinella spp.) and anchovy (Engraulis encrasicolus). One of the particularities of this system is the presence of the Canary archipelago, which is close enough to the continental coast to allow exchange of biological material between the two areas. We used intermediate-resolution (7 km) hydrodynamic simulations as inputs for an individual-based model to assess the transport of ichthyoplankton (i) along the African coast and (ii) from the African coast to the Canary archipelago. We explored different scenarios of passive versus active vertically swimming larvae to assess the possible impact of vertical migration on transport and retention. Transport along the coast was essentially southward. The zone located between Cape Draa (similar to 28 degrees 45'N) and Cape Juby (similar to 27 degrees 56 N) had relatively high levels of retention in autumn and winter. The zone extending from Cape Boujdor (similar to 26 degrees 12'N) up to Cape Blanc (similar to 21 degrees N) had high retention levels during the entire year. Larvae transported from the coast to the archipelago came mainly from the area located between Cape Ghir (similar to 30 degrees 38'N) and Cape Juby, whereas larvae retained in the eddy field downstream of the islands originated mainly from the area between Cape Juby to Dakhla (similar to 24 degrees N). The results are discussed in relation to available field data of anchovy and sardine egg distributions over the continental shelf, and compared with oceanic surveys of larval presence near the Canary archipelago.