Effects of the river discharge management on the nursery function of the Guadalquivir river estuary (SW Spain)

Abstract

Within the Guadalquivir estuary, young recruits of marine species seem to respond to changes in freshwater flow by moving with the mass of estuarine water that is most ''suitable'' for them. The control of the river flow, from a dam 110 km upstream from the river mouth, has an immediate effect on the estuarine salinity gradient, displacing it either seaward or upstream. Consequently, there is a reduction or enlargement of the estuarine area that is used as nursery grounds. The analysis of the temporal estuarine recruitment and spatial distribution of young stages of marine species, during six annual cycles, provides evidence that the estuarine zone used as nursery grounds is mainly that part situated seaward from an isohaline value of 5. The relationship between the position of that isohaline (D 5 ) and the freshwater discharges from the dam was also examined during high and low tides. It was found that a high percentage of the isohaline position variation (75% and 73% at high and low tides, respectively) can be explained by the freshwater volume discharged from the dam during the previous week. These preliminary results suggest that an accurate model of the relationship between these two variables may be a useful tool for future management strategies of freshwater discharges to the estuary.

Modelling the possible effects of climate change on an Australian multi-fleet prawn fishery

“…The impact of changes to river discharge levels is of particular importance for several species, both in terms of the sustainability of the species and the fisheries that exploit them (Esmaeili and Omar 2003;Fernández-Delgado et al 2007). Fortunately, improvements in both technology and assessment techniques have given scientists greater capacity to evaluate the possible impacts of such changes.…”

Daily otolith growth and ontogenetic geochemical signatures of age-0 anchovy (Engraulis encrasicolus) in the Gulf of Cádiz (SW Spain).

“…1), where eggs are found in large concentrations (Rubín et al, 1997;Bellido et al, 2000;Baldó et al, 2006;Catalán et al, 2006a;Ruiz et al, 2006). Early larvae are primarily found in the Gulf close to the estuary (Baldó et al, 2006;Ruiz et al, 2006), and late larvae and juveniles are captured in large amounts in the first 32 km upstream of the river mouth Sobrino et al, 2005;Drake et al, 2007;Fernández-Delgado et al, 2007). The role of the Guadalquivir estuary as a nursery ground for anchovy has been postulated for some time (see references above), but whether all or part of the fished stock is linked to the estuary, and at which life stages, remains unknown and is crucial for management.…”

Temporal and spatial variability in the Guadalquivir estuary: a challenge for real-time telemetry

“…In spite of its importance, until very recently, only a few studies have been carried out in the estuary; these have focused mainly on fisheries, crustacean decapods Fernández-Delgado et al 2007;González-Ortegón et al 2010), and chemical contamination following the Aznalcollar mining waste spill (Grimalt et al 1999;Blasco et al 1999). Three years ago, to obtain a better understanding of the physical and biological processes governing the estuary ecosystem, an interdisciplinary research program was established, with the following main goal: "to develop an integral method to diagnose and forecast the consequences of human actions on the Guadalquivir estuary."…”