Sardine and horse mackerel recruitment and upwelling off Portugal

Abstract

The results of preliminary investigations on the possible relationships between coastal upwelling variability observed with satellite remote sensing, and sardine and horse mackerel recruitment dynamics in the west coast of Portugal are presented. The analysis of a sardine-recruitment time-series for the period 1976–1998 shows that there has been a decreasing trend since 1983 (with the exceptions of 1991 and 1992), the years from 1993–1995 representing the lowest values in that time series. Horse mackerel exhibited a decrease from 1986 until 1990, and from 1992–1995, the latter representing the lowest value for the period 1986–1998. Sea surface temperature (SST) derived from satellite data were used to compute monthly SST upwelling indices along the Portuguese west coast over a period from 1987–1997. The analysis focused on seasonal and annual upwelling variability off Portugal, and its possible effects on sardine and horse mackerel recruitment to the fishery. An increasing trend in SST upwelling indices during the winter (January–March), especially between 1992 and 1995 was found. The upwelling events observed off Portugal during winter months, which correspond to the spawning season for sardine and horse mackerel, had a negative impact on the recruitment of these fish species. This effect on recruitment could be due to an increase in conditions favourable to the offshore transport of larvae and consequently an increase in their mortality. Prior to 1992, when no upwelling events occurred during winter, recruitment dynamics was closely linked with the spring–summer seasonal upwelling variability off the Portuguese west coast.