Visbestandopnames in Vlaamse beken en rivieren afgevist in het kader van het 'Meetnet Zoetwatervis' 2007

In this document we report about the surveys performed within the framework of the freshwater monitoring network. We assessed the fish assemblages in 149 sites in nine different river basins. Among the rivers we fished in the Dijle, the Leie and the Zenne. Fish assemblage data were obtained by electrofishing using a 5 kW generator with an adjustable output voltage of 300 to 500 V and a pulse frequency of 480 Hz. The number of electric fishing devices and the number of hand-held anodes used was 2 except when the river was smaller than 1 m. We sampled also fish using double fyke nets (type 120/80). Fish data recorded included speciesspecific fish densities, individual total lengths (TL) and wet weights (g). On each site we recorded different abiotic parameters. We give for each river basin the results of the fishing campaigns. In the River Dijle basin we surveyed the Dijle and some of its tributaries. The ecological quality of the River Dijle downstream Leuven improved compared to previous campaigns. The upstream locations have a better quality but in general we observe a positive evolution in the fish population. For the first time fish was caught in the River Zenne which is rather a remarkable result since this river had a reputation as an open sewer for years and is only recently purified. In the other tributaries we could only observe an improvement in the Voer. In average the sites in the River Dijle basin have a poor quality. In the River Demer basin we surveyed two tributaries each of them showing a decrease in water quality which is reflected in a poor score for the index of biotic integrity (IBI). In the River Nete Basin and River Maas basin we could not see a change of quality compared to previous surveys. Most of the locations score a moderate quality. 25% of the assessed sites in the River Maas basin have a good quality. In the River IJzer basin a positive trend was observed but the IBI still scores poor in most sites. A similar trend is observed for the water courses within the Gentse Kanalen which in average score moderate. In the basin of the Schelde (upstream Gent) we recorded a status quo camparing to previous surveys. The IBI of these water courses score bad or poor. In the River Leie basin we fished in the River Leie and some tributaries e.g. Heulebeek and Mandel. For the River Leie the positive trend observed in 2003 was confirmed. Species diversity and density increased spectacularly. And in average the river obtains a moderate IBI score. A quality improvement in the section between Deinze and Kortrijk is remarkable but most fish was caught in the so called “tourist Leie”. For the first time in the River Leie basin Stone loach was caught. In the River Schelde basin downstream Gent we surveyed some tributaries. In half of the sites no fish were caught and the other sites score mostly poor. A moderate quality was recorded in the Zwanebeek and the Zuidelijke Watergang. In the Barbierbeek a slight improvement was observed

Visbestandopnames in het Lippenbroek, een gecontroleerd overstromingsgebied met gereduceerd getij in het Zeeschelde-estuarium: viscampagnes 2006-2012

Between 2006 and 2012 researchers of the Research Institute for Nature and Forest (INBO) performed several fish surveys in the Lippenbroek. This is a reduced flood controlled tidal area along the River Zeeschelde nearby Hamme. The ten acre area has been active since March 2006 with water entering and leaving the area daily. The reduction of the tide allowed the development of different habitat types and the creation of mud flats and marshes. We selected three types of habitats: the reservoir situated at the sluices an adjacent creek and a permanently flooded pool. Fish techniques used were electric fishing and fyke netting.In total 20 fish species were caught. With fykes we captured 16 species in the creek and 17 in the reservoir. With electric fishing 8 species were caught in the creek, 11 in the reservoir and 17 in the pool.Over the years smelt, common goby, flounder and roach dominated in numbers the fyke net catches in the creek. In the reservoir roach, Prussian carp and stone moroko were dominant. With electric fishing the most abundant species were stone moroko and flounder in the creek while in the other habitats threespined stickleback and stone moroko were the most abundant species.Statistical analysis with fyke net data showed that the species composition changed over the years in both the creek and reservoir. However, there was no indication of different fish composition in the two habitats. In addition, no seasonal patterns could be found.The statistical analysis with fish data from the pool revealed again a change in fish composition over the years. Although flounder and common goby disappeared from this habitat, an increase in species and individuals caught was apparent. No seasonal pattern could be seen.The length frequency distribution indicated that Prussian carp, stone moroko and roach spawn in theLippenbroek. Prussian carp larvae occur mainly in the pool while the other larvae are found especially in the creek and reservoir. These species also use the Lippenbroek as a nursery. Perch uses the creek and reservoir as a nursery while larger species are captured in the pool.Diadromous species as flounder and smelt use the area as a nursery. Juvenile smelt occurs especially in the creek. Flounder migrated from the pool to the creek and reservoir.The common goby, a typical estuarine species, also disappeared from the pool and uses now mainly the creek as a nursery and permanent residence.Seabass is a marine species using the Lippenbroek as a nursery ground. The smallest individuals are found in the creek. The larger specimens occur in the reservoir. In the pool we also caught some seabass.Pikeperch is foraging in the reservoir; the smaller individuals are growing up in the creek. This species is not captured in the pool.The habitat diversity influences the fish diversity. E.g. less frequently caught species such as white bream and carp were captured mainly in the creek. Pumpkinseed and rudd were caught especially in the pool.Bream and eel occur mainly in the reservoir while bitterling has no apparent habitat preference as it was captured regularly in all habitat types

Opvolging van het visbestand van de Zeeschelde: resultaten voor 2011

In researchers of the Research Institute for Nature and Forest (INBO) performed three fish surveys in theZeeschelde estuary. Fish assemblages were surveyed in six locations nearby the banks during spring, summer and autumn using paired fyke nets.In total 33 fish species were caught. Largest numbers of fish were caught mainly in spring. In summer we caught the highest number of individuals. Fish assemblages in each location are different.Flounder is the most abundantly caught species in the Zeeschelde. In spring smelt and three-spined stickleback are caught in large numbers. In summer flounder and common goby are the most abundant species. In autumn we mainly caught flounder and smelt.Statistical analyses indicated a significant temporal and spatial difference in fish assemblages. Even within one location seasonal and yearly changes occur.The presence of large numbers of twaite shad and smelt was remarkable.The fish-based index indicated that the mesohaline zone is no longer in the “moderate” status but in a “poor” status. The decrease in number of individuals caught is an indication of ecological degradation. The oligohaline zone remained in a “poor” status. The freshwater zone now has reached the “GEP” status.The length frequency distribution indicated that the following species use the estuary as a nursery: flounder, seabass, herring and sole. Other species spawn in the estuary: roach, bream, smelt and twaite shad.Data obtained from the volunteers added nine more species to those caught by the INBO

Opvolging van het visbestand van de Zeeschelde met ankerkuilvisserij: Resultaten voor 2013

In 2013 researchers of the Research Institute for Nature and Forest (INBO) performed three fish survey campaigns in the Zeeschelde estuary. Fish assemblages were surveyed with anchor netting in Doel, Antwerpen, Hingene and Branst during spring, summer and autumn. In total 42 species were caught. The highest number of species was caught in spring. In the Zeeschelde the mesohaline zone contains the highest number of species. Again smelt was the most abundantly caught species. The presence of larvae, juveniles and adults allows us to conclude that the estuary provides spawning habitat and act as a nursery for this species. Adult twaite shad was caught again. However, although the presence of eggs was established in spring, no larvae were caught in summer or autumn. Apparently recruitment was not successful this year. During the autumn campaign juvenile anchovy, herring and seabass were caught indicating that marine species use the estuary as a nursery habitat. Presence of glass eel confirms observations that this year was a good year for glass eel migration into our estuaries. The capture of houting is at least remarkable as this species is considered extirpated in the Zeeschelde. Shrimps and prawns are, even far upstream, abundant in the Zeeschelde