Modelling the effect of environmental and anthropogenic factors on the abundance of early life-history stages of the European sardine in the Guadalquivir estuary

Abstract

Estuarine coastal areas play an important role in the recruitment of some small pelagic fish populations mainly when stable salinity-gradients are present. Damming of these ecosystems results in major alterations in this natural hydrological regime. Therefore, changes in the marine/freshwater balance can result in services loss, like the nursery habitat estuaries provide to small pelagic fish, such as sardines. Our previous work showed that the main important recruitment of sardine occurs in spring when this water balance is more variable. However, the drivers of sardine recruitment and particularly the interactive effects of environmental (temperature, salinity, turbidity and winds) and anthropogenic (freshwater discharges) factors are largely unknown. We modelled these effects on the abundance of sardine larvae and juveniles in the Guadalquivir estuary, the most southwestern one in the Atlantic Europe. Sardine early stages tend to occur at the most seaward and more saline sampling site in our study area. The best selected models included the freshwater flow and the wind regimen (northern-southern component) as main drivers explaining their abundance. Freshwater input –tightly controlled by a dam– had a negative short-term effect on the abundance of juvenile sardines above a critical threshold. On top of this, the wind-speed variability in the northern-southern direction showed a clear linear effect: with strong northerly winds enhancing the sardine abundance in the Guadalquivir estuary. These results contribute to the knowledge of the recruitment process of the European sardine and eventually to implementing an ecosystem approach to its fishery in the Gulf of Cadiz.