Causes of spawning pattern variability of anchovy and hake on the Patagonian shelf

The hake and anchovy are the most important demersal and pelagic resources on the Argentine shelf. Both species have a common geographical range, as they are trophically linked: the anchovy is one of the main food items of the hake during their adult stages. While the hake is heavily exploited, with clear signs of overfishing, including a seriously reduced spawning biomass, the anchovy is relatively unexploited. Traditionally both species have shared the same reproductive scenarios off Patagonia characterised by tidal mixing fronts acting as larval retention areas. This paper reviews the spawning and nursery ground of both species since early 1970’s. The most striking result is the gradual disconnection of the hake from the traditional spawning grounds, which are still occupied by the anchovy. The typical hake spawning concentrations are now dispersed and located offshore, while the anchovy maintains the classical pattern in close association with the frontal system. An analysis of the hydrographical conditions prevailing in the spawning grounds shows no significant changes that could account for this anomalous hake behaviour. The implications of these changes on recruitment and population dynamics of both species are discussed in this paper.