Natural and anthropogenic factors in the Guadalquivir estuary affect the abundance of anchovy in the Gulf of Cadiz (SW Spain)

Abstract

The Gulf of Cadiz socio-ecosystem is characterized by a focal ecosystem component –the estuary of the Guadalquivir River– that has an in uence on the marine ecosystem –serves as a nursery area– and at the same time concentrates a great number of sectoral human activities. This nursery role particularly affects the anchovy fishery, which is the most economically and culturally important fishery in the region. As a transition zone between terrestrial and marine environments, estuaries are particularly sensitive to human activities, either developed directly at the aquatic environment or its surroundings. A dam 110 km upstream from the river mouth regulates freshwater input (mainly for agriculture purposes) into the estuary with consequences on turbidity and salinity. Using time series analysis on 18 years of monthly data from an estuarine monitoring program we (1) quantify the effects that natural (plankton, temperature, winds) and anthropogenic-influenced variables (freshwater volume, turbidity, salinity) have on the abundance of anchovy larvae and juveniles, and (2) relate the abundance of these estuarine-resident early stages to the abundance of adult anchovy in the sea. Water management stands out as a key node where potentially con icting interests (agriculture, power generation, aquaculture, fisheries) converge. Linking land-based activities to its impact on stock biomass represents the main challenge to ecosystem-based management in this particular regional sea. By focusing on the effects that these activities ultimately have on the anchovy fishery –via recruitment– our study aims to contribute to the process of making the ecosystem approach operational in the Gulf of Cadiz.