Sardine and horse mackerel recruitment and upwelling off Portugal

The results of preliminary investigations on the possible relationships bet ween coastal upwelling variability observed with satellite remote sensing, and sardine and horse mackerel recruitment dynamics in the west coast of Po rtugal are presented. The analysis of a sardine-recruitment time-series fur the period 1976-1998 shows that there has been a decreasing trend since 19 83 (with the exceptions of 1991 and 1992), the years from 1993-1995 represe nting the lowest values in that time series. Horse mackerel exhibited a dec rease from 1986 until 1990. and from 1992-1995, the latter representing the lowest value For the period 1986-1998. Sea surface temperature (SST) deriv ed From satellite data were used to compute monthly SST upwelling indices a long the Portuguese west coast over a period from 1987-1997. The analysis f ocused on seasonal and annual upwelling variability of Portugal, and its po ssible 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 observe d off Portugal during winter months, which correspond to the spawning seaso n for sardine and horst: mackerel, had a negative impact on the recruitment of these fish species. This effect on recruitment could be due to an incre ase in conditions favourable to the offshore transport of larvae and conseq uently an increase in their mortality. Prior to 1992, when no upwelling eve nts occurred during winter, recruitment dynamics was closely linked with th e spring-summer seasonal upwelling variability off the Portuguese west coas t. (C) 2001 International Council for the Exploration of the Sea.