A reduction of inflow to the Guadiana River on the border between Portugal and Spain may directly contribute to the degradation of fish habitats. Changes are expected to the spawning behaviour of Engraulis encrasicolus adults, to the migration patterns of larvae in the estuary, and to the catches of fisheries in the lower part of the river and adjacent coastal areas. Spawning of E. encrasicolus occurs in the lower part of the estuary and in the adjacent coastal areas. However, high abundances of larvae have been registered in the middle and upper parts of the estuary, the most productive region of the estuary, that with the estuarine turbidity maximum (ETM). In a year of normal inflow, such as the hydrologic year 1987–1988, some retention of larvae occurred in this area. However, in an abnormal hydrologic year with a low inflow (1999–2000), and with an increase in freshwater inflow during the spring months, a disturbance to the migration pattern seems to have affected the survival of larvae in the estuary. High river inflow, probably associated with an increased input of nutrients, appears to have an important and positive effect on adult numbers, because anchovy fishery catches in the adjacent coastal area increased under these conditions.
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