Natural and anthropogenic effects on the early life stages of European anchovy in one of its essential fish habitats, the Guadalquivir estuary

Essential fish habitats (EFHs) are all aquatic habitats and substrates fundamental for spawning, breeding, feeding and/or growing to maturity. Estuaries are a good example of this because they play an important role as nursery grounds for several marine species. Despite their importance for completing the life cycle of some fish stocks, little is known about how early stages of these species respond to changes within estuarine environments. Understanding the response of fish juveniles to combinations of multiple drivers in these highly dynamic ecosystems is not straightforward. By analysing an 18 yr time series of European anchovy Engraulis encrasicolus and 3 mysid species in the Guadalquivir estuary (SW Spain), we quantified the effects of both natural and anthropogenic factors on the early stages of this small pelagic fish and its prey. Of the factors assessed, freshwater discharges and turbidity-both influenced by human activities- showed a remarkable effect on the abundance of anchovy. Natural environmental variables such as temperature, salinity, winds and prey abundance were also important. The relationship between anchovy and mysids suggests that the Guadalquivir food web is predominantly resource-driven and that indirect environmental effects can cascade up through a web of interactions. This study provides empirical information on the response of anchovy to environmental changes within its main essential habitat in the Gulf of Cadiz. Since the human-influenced variables can be managed to some extent, we discuss their implications for maintaining a healthy EFH, which in turn would contribute to developing an ecosystem approach to fisheries management in the region.