Early Life Survival of the AnchovetaEngraulis ringensOff Central Chile during the 1995 and 1996 Winter Spawning Seasons

Abstract

For fish populations occurring in coastal upwelling areas, the timing of spawning has been proposed to occur during seasons when transport offshore is reduced. Along the coastal zone off central Chile, the anchoveta Engraulis ringens spawns preferentially during winter. Spawning in this season, however, might represent a period of increased risk to eggs and larvae due to the harsh and variable oceanographic conditions. This study determined the mortality rates of egg and larval anchoveta in an area located close to the species' southern limit of distribution during its winter spawning season. Two temporal scales of variability, interseasonal (between years), and intraseasonal (individual daily cohort mortality rates) show that (1) mean seasonal mortality rates were not different between years and (2) mortality rates considering the egg and larval stages together (96% daily in 1995 and 98% daily in 1996) were much higher than those estimated using only the larval stage (4.4% daily in 1995 and 6.8% daily in 1996). The results of the individual cohort mortality rates, especially in 1995, revealed a tendency toward a decrease in mortality rates as the winter season progressed (from 52 to 9% daily). Because the maximum egg abundance in the water column occurred early in the season in 1995, we propose that the largest fraction of the mean seasonal mortality was due to egg mortality occurring early in winter. The information on the environmental characteristics and the reported larval growth rates in different periods during the winter spawning season do not support the hypothesis of larval food limitation but, instead, suggest that oceanographic factors (e.g., cross-shelf transport, low water temperature, presence of river plumes) play a major role in the development and success of the early life stages in this southern spawning area.