Are Portuguese coastal fisheries affected by river drainage?

Abstract

The Portuguese coast is particularly adequate for studies on the impact of climate change on fisheries, as it has faced an increase in both air and sea surface temperature and a decrease in intensity and frequency of rainfall. Ecological responses to climate change have already been observed in Portuguese waters, with consequences in fisheries. Regional climate models have predicted a further decrease in rainfall in Portugal by the end of the century, which will have a strong impact on the runoff into coastal areas. River drainage affects the physical, chemical and biological properties of coastal ecosystems, regulating habitat availability and favouring their productivity. The present study analysed the influence of river drainage on landings of coastal ports in the vicinity of four hydrologically distinct estuaries. Unlike previous results obtained for the Mediterranean, no significant relationships between river drainage and landings were found. Relationships between drainage and landings can be inconsistent among regions and dependent on how strongly a food web relies on nutrients and organic matter of river origin. In the Portuguese coast, an upwelling regime is of particular importance for the richness and diversity of the coastal ecosystem and for fisheries. The complexity of the coastal upwelling phenomenon together with a possible interaction of several other smaller scale factors acting on recruitment of commercial species may mask the effects of river drainage on landings. Nevertheless, as accentuated decreases in rainfall have been predicted for Portugal, the resulting reduction in river drainage may still strongly impact fisheries in the future.