Abstract

Previous studies on clupeiform reproduction have suggested that in upwelling areas of permanently high wind speed, winter spawning could be selected to promote the retention of offspring close to the coast, where more benign conditions are supposed to exist. The role of winter environmental characteristics, other than those conducive to retention, that could represent trade-offs within this strategy (i.e, larval food limitation, water temperature, intrusion of oceanic predators), however, have traditionally not been assessed. In the present paper, we assess the role of environmental variability on the winter reproductive strategy of the anchovy Engraulis ringens in an area close to its southern limit of distribution. A series of 8 cruises were conducted during the winter of 1995 in the coastal zone off Talcahuano (37 degrees S). Wind field, satellite sea surface temperature and hydrographic characteristics of the water column revealed strong short-term variability of oceanographic conditions in the nearshore area. During winter, upwelling events, a broad river plume and a cross shelf circulation were determined. Peak anchovy egg and larval densities occurred regularly at the nearshore stations. Increases in larval densities at an offshore station (12 nautical miles offshore) coincided with periods of coastal upwelling and the presence of a broad river plume, suggesting rapid transport of larvae from the coast. Maximum densities of gelatinous predators, in turn, coincided with the periods of minimum larval densities offshore, creating an apparent inverse relationship. Predators and larvae, however, did not co-occur in the same water masses, as revealed by the sea surface temperature and hydrography. Despite winter conditions, overall microplankton density in the water column was high during most of the season, with maximum anchovy egg and larval densities co-occurring with peak periods in larval food abundance. The coupling between maximum egg and larval fish density and specific meteorological and oceanographic conditions, the temporal and spatial decoupling between potential gelatinous predators and larval anchovies, and the overall benign larval feeding conditions close to the coast suggest that the timing of spawning and location of young anchovies nearshore may be part of a larger reproductive strategy of this species in the area.