Modelling the transport success of anchovy Engraulis encrasicolus eggs and larvae in the southern Benguela:: the effect of spatio-temporal spawning patterns

Recruitment success of anchovy Engraulis encrasicolus in the southern Benguela is thought to depend largely on the passive transport of eggs and larvae from their warm-water spawning area, located in the southern part of their distribution range (Agulhas Bank), to their cold-water nursery grounds located 500 km away on the west coast of South Africa. In order to test this hypothesis, the output of a 3D hydrodynamic model was coupled to a particle-tracking model, allowing the quantification of different factors such as the timing and precise location of spawning activity, the frequency of spawning activity within a month, the level of aggregation of the spawning stock, and the interannual variability of transport due to mesoscale processes. Results from the model indicate that spawning season and area have a major effect on transport success. The most favourable period for spawning was September to March, peaking in November, and the western Agulhas Bank was the most favourable spawning area. A low success rate of passive transport to the core inshore nursery area in the model suggests that additional processes such as swimming or advection are required for larvae to reach this area. In general, there was good agreement between observed spawning patterns and the optimal temporal and spatial strata where particle transport was most successful, suggesting that the spawning strategy of anchovy is mainly the result of an adaptation to the circulation patterns in the region. Nonetheless, some discrepancies were observed between the success of transport and actual spawning patterns, and temperature may also be an important factor to take into consideration to fully explain how this originally temperate species is able to survive in an area of highly contrasting temperatures.