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INBO researchers surveyed fish assemblages in several future flood control areas along the Zeeschelde estuary (Fig. 1, Table 1). Two survey periods were performed at 11 sites (117 surveys in toal). Fish assembvlages were assessed using electric fishing and fyke netting. Physical and chemical recordings showed that the 25% of the sites had a too low oxygen concentration. Some sites had no fish. In total 25 fish species were recorded. In the text fish results are explained for each area. In genral bitterling, stone moroko, Prucian carp, three-spined stickleback, roach and pumpkinseed dominate in numbers. The results indicate the presence of a diverse fish assemblage of mainly eurytopic and limnophilic species in some sites.

De mens maakt gebruik van een brede waaier aan diensten en grondstoffen die door ecosystemen worden geproduceerd. Deze zijn algemeen gekend onder de noemer ‘ecosysteemdiensten’. In Vlaanderen zijn ecosysteemdiensten nog maar weinig ingeburgerd. Toch bezit het concept een heel groot potentieel om een bredere basis te geven aan het natuurbehoud in Vlaanderen. Al te veel wordtnatuurbehoud nog gezien als een fenomeen met beperkte maatschappelijke relevantie: economische ontwikkeling gaat dikwijls voor omwille van de korte-termijn winsten. Het beschrijven en evalueren van ecosysteemdiensten laat toe om meer onderbouwde beleidskeuzes te maken in functie van een duurzame ontwikkeling van Vlaanderen, waarbij de vereiste integratie van economie en ecologie wordt gemaakt. Om deze benadering ook in Vlaanderen ingang te doen vinden is er dringend behoefte aan meer inzicht in de ecologische processen, meer kennis over de status van de ecosysteemdiensten en van de eindigheid van de winsten die eruit voortvloeien. Het begrijpen van ecosysteemdiensten vereist een stevige basis in de ecologie, die de onderliggende principes en interacties tussen organismen en hun omgeving beschrijft. Deze opdracht wil hiervoor de basis leggen.

The protection of nature values and functioning of aquatic ecosystems is the subject of several legal commitments and international agreements. European legislation includes the Water Framework Directive (WFD) as well as the Wild Bird and Habitat Directives (BHD). In addition, different competences derive from local, regional, national or multilateral and international initiatives, each with its own objectives and targets. Clearly these commitments apply on different spatial scales (Europe, North Sea area, country, river basin). Consequently, evaluations of present regulations that aim to protect environments optimally adopt an integrated, hierarchical structure. Under this approach, particular commitments aim at sustainable and integrated management but may focus on a different spatial level of the ecosystem and its functioning. Accordingly, objectives at each level aim at proper functioning of the ecosystem in a way that the commitments are respected. Each level feeds back to the higher level in order to avoid contradictions. Once the objectives are set, quantitative indicators or measurement endpoints have to be defined to measure the actual status and to compare the ecosystem state with references set by the conservation goals. Depending on the scale, indicators are either based on integrated data or represent an explicit measure of the state of the ecosystem. Therefore, any monitoring scheme should provide a wide range of information so that for each level of assessment the necessary information can be deduced. Restoration measures will then aim at restoring the processes that generate the required habitats and species populations. The potential for recovery remains since most species and functional groups persist, albeit in greatly reduced numbers. This proposal describes habitat needs for fish in estuaries, defined as parts of a river under tidal influence, to assure a good status of fish populations as defined by the Water Framework Directive (EU Water Framework Directive, WFD, 2000). This good status is obtained when the conservation goals are fulfilled. A good habitat quality, a proper ecosystem functioning and a good carrying capacity will assure that conservation goals are achieved. Conservation goals for fish are refined. The tidal Schelde is taken as a case study but this approach can be applied to all North Sea estuaries. As such, this report informs to the objectives of the HARBASINS project. In particular, the HARBASINS project addresses the question as to how different approaches by regions in Europe, with respect to legal implementation of European law and site specific management experiences, result in improved estuarine functioning and health as reflected by the structure of the estuarine fish community. In this context, estuarine fish are used as a top component in the ecosystems and one which has a high public and political resonance, hence often being (with wading birds) the end point for the management of the systems. An accompanying report will consider similar aspects for estuarine wading birds. HARBASINS - Conservation goals. In this report, and in order to make the method widely applicable and thus not reliant on the particular species inhabiting any single estuary, we firstly classify fishes into guilds with relevance for the formulation of conservation goals. We describe general and guild-specific conservation goals for fish. Based on literature, habitat requirements are defined and then this information is used to define habitat needs allowing a general functioning of the estuarine ecosystem and provide some suggestions to achieve these needs. In addition we describe habitat needs at a guild level. A fish-based tool to assess the present status relative to the conservation goals will be developed and reported in another document.

This paper presents a new approach which was developed to find an optimal combination of candidate metrics for creating a fish-based estuarine biotic index (EBI) for defining the quality status of an estuarine area. The key idea was that a powerful index should minimise two prediction errors simultaneously: falsely declaring the status of a site as disturbed while it is not (Type I error) and the reverse, falsely declaring a disturbed site as undisturbed (Type II error). The balance between both errors is an inherent characteristic of an index and can be displayed as a curve. The area under this curve (AUC) is a measure of the misclassification rate (smaller = better). This criterion was the basis for a stepwise approach whereby in each step a metric resulting in the highest reduction of AUC was added. Five metrics were selected and the distribution of their average was the basis to derive the thresholds for the classes of the EBI. This paper presents the fish-based index (EBI) for the brackish Schelde estuary in Flanders (Belgium). The index was calibrated against fyke net data from five sites during the period from 1995 to 2004. The sites ranged in quality from moderately impacted to very disturbed, classes 3 to 5 respectively. Despite there being neither of the highest classes 1 (high) and 2 (good), the EBI presented can serve as an evaluation tool in the highly impacted situation in Flanders as it discriminates well between moderate and highly impacted sites. In addition, its definition complies with the biological status classes of the European Water Framework Directive (WFD).

We surveyed the River Rupel and River Durme, Flanders, between 10 and 13 April 2006. Both rivers are transitional waters belonging to the Scheldt estuary. The Durme River is a tributary of the Scheldt River in Flanders. It is a relatively small tidal river. Dredging occurs in certain areas. The valley consists of generally low-lying terrain, which is currently nearly entirely protected by dykes against the tides. The Rupel connects the Rivers Nete, Dijle, Zenne, Demer and Gete with the River Scheldt. It is notorious for being heavily polluted. Fish assemblage data were obtained using fyke nets placed for a period of 24 hours. The nets were placed at low tide, emptied the next day at low tide and removed. We surveyed three sites in each river using two fyke nets per site. Table 1 and the map in annex provide the co-ordinates of the sites. Table 2 gives the methodology used.Table 3 provides the descriptive information of the sampled sites and the abiotic variables (oxygen concentration, conductivity and water temperature) which were recorded during the survey.Fish data include species, individual total length and weight. Table 4 gives an overview of the collected species according to the methodology used. Table 5 represents morphometric information of the species per location.Table 6 presents the catch per unit effort per species. In the River Rupel ten different species were collected. This is due to the incoming Scheldt water. In general the water quality is bad due to the River Zenne.Although more species and specimens were collected in the River Durme, there were still less species than one would expect in a pristine water of this type. In total 12 species were collected. In 2006 the purification of the River Zenne should lead to an increase of the water quality. This should have its effect on the River Rupel and the River Scheldt too. Further surveys will allow us to assess the trends in these very dynamic systems.This report is a contribution to the European Interreg IIIb North Sea project Harbasins, aimed at harmonising European river basin management.