Sustainable management of a coastal lagoonal system (Ria Formosa, Portugal): An ecological model for extensive aquaculture

Abstract

Abstract. The Ria Formosa lies in southern Portugal, extending for about 55 km. It is a true barrier island system, comprising mainland, backbarrier lagoons, inlet deltas, barrier islands, barrier platforms and shoreface. Of the Ria Formosa system, which covers a total area of 163 km% 20 km 2 are occupied by salinas and aquaculture ponds. The main water reservoir of the salinas and the extensive aquaculture ponds behave like small lagoons where there are one or more openings to a tidal channel. These small lagoons have the advantage of being easy to study and to model.An ecological model was developed to estimate the potential production of the gilthead seabream in the Ria Formosa, in an extensive aquaculture regime. This model was based on information concerning chemical and physical factors (forcing functions) and secondary production estimates from four sites in the Ria Formosa with different environmental conditions, where extensive aquaculture is practised. Published information on optimal growth parameters of the gilthead was used to build the model, which was based on some assumptions concerning the detrimental effect of an excessive increase of salinity and other environmental factors both on gilthead growth (one state variable) and on prey production (divided into two state variables), which is essentially benthic macrofauna.Reservoirs with low water renewal undergo large environmental fluctuations. The growth of gilthead or other fish can be difficult, not only because of the adverse environmental conditions but also because of the low secondary production. The maximum yield of fish is predicted to be less than 6 g m -2. In reservoirs where the water exchanges on almost every tide, the maximum yield of gilthead can be in excess of 22-25 g m -2. Nevertheless, the high productivity of these sites in terms of secondary production of benthos and fish, as well as primary production, can lead to oxygen depletion during the night or at day-break. An attempt to further improve fish production by fertilisation or by adding food could provoke a rapid deterioration of the water quality and endanger all production.

Use of hydrodynamic and benthic models for managing environmental impacts of marine aquaculture

“…• Portugal: ecological models for extensive aquaculture in Portugal have linked high aquaculture activity with oxygen depletion, with fish production being dependent on natural food availability and environmental conditions (Gamito 1997). No regulation takes place using these models.…”

Effects of dietary protein levels on the long-term growth response and fitting growth models of gibel carp (Carassius auratus gibelio)

“…In animals, growth curves are generally S-shaped and based on long-term growth datasets ( De Graaf and Prein, 2005 , Ersoy et al., 2006 , Yang et al., 2006 ). Gompertz, logistic, Richards and von Bertalanffy models are often used to fit growth curves of fish, especially for the time-growth response estimation, which much better than ANOVA or broken-line models ( Jiang and Qin, 1996 , Gamito, 1997 , Gamito, 1998 , He and Stewart, 2002 , Hernandez-Llamas and Ratkowsky, 2004 , Ersoy et al., 2006 , Russo et al., 2009 ). Studies on long-term growth curves of animals are of major importance for dynamically understanding the process of growth and responses on dietary nutrient density as well.…”

Using Model‐Based Inference to Select a Predictive Growth Curve for Farmed Tilapia

“…The Gompertz growth model (Gompertz 1825) is a sigmoidal growth curve that derives from models of self-limited growth where rate of growth decreases exponentially with size (Karkach 2006). It has been applied successfully to wild, juvenile fishes (Andrade 1992;Gamito 1997). At the early stage of the life cycle, fish growth is very fast compared with later stages.…”