VIS - Fishes in estuarine waters in Flanders, Belgium

Study Extent

Over 2,000 locations in estuaries, inland rivers, streams, canals, and enclosed waters in Flanders, Belgium have been sampled, from March to November, since 1992. In 2001, these locations were consolidated in a monitoring network (“VISmeetnet”) of 900 sampling points. Four locations in the Yser estuary and 43 locations in the Scheldt were sampled since 1995. While the Yser estuary only covers a small geographical area, the Scheldt estuary is with 33,000 hectares one of the largest estuaries in Europe. It is also one of the few remaining European estuaries that includes the entire gradient from fresh to saltwater tidal areas (Van den Bergh et al. 2009). The 43 sampling locations in the Scheldt estuary are mainly located in the River Scheldt, but also in the Rivers Durme, Rupel, Dijle, Zenne and Nete. The geographic coordinates in the dataset are those of the defined sampling locations (dwc:locationID). However, as these coordinates are not always exact the actual coordinates of the catch, which may be located further up- or downriver, the coordinate uncertainty (dwc:coordinateUncertaintyInMeters) has been set to 250 meter.

Sampling

Standardized sampling methods were used as described in Belpaire et al. (2000) and Van Thuyne & Breine (2010) and are specified in the dataset as dwc:samplingProtocol. Per water body, the same method was used for each sampling event. The default method is paired fyke netting, which has been intercalibrated by the North East Atlantic Calibration Group, but additional techniques such as anchor netting, seine netting, pound netting, electric fishing, and eel fyke netting were used as well (Breine et al. 2011). All fishes were identified to species level, counted and their length and weight was measured. Fyke nets are relatively unselective fishing gear catching demersal and pelagic species (Hamerlynck and Hostens 1994) and also they are easy to install in a great variety of habitat types. As few studies compare fyke catches with other gear (e.g. Hinz 1989, Thiel and Potter 2001), we compared presence/absence data obtained with fyke nets with presence/absence data of fish impinged at cooling-water filter screens of the nuclear power plant of Doel situated in the study area. The data was collected in the same period between 1995 and 1998. During this period we collected the same species with both survey methods but the species richness per day per fyke net was generally higher than that obtained on the filter screens (Breine et al. 2007). In addition preliminary results from a gear intercalibration exercise in different estuaries in Ireland (Whyte et al. 2007) indicated that for species diversity, the results of fyke net catches are comparable to those obtained with other gear (beach seine, beam trawl, otter trawl).

Quality Control

Strict field protocols where used. The Manual for Application of the European Fish Index (EFI) (Fame consortium 2004) served as a guideline for electrofishing and was used in support of the EU water framework directive.

Method steps

1. Water type: Estuaries Method: fyke fishing, anchor netting, pound netting, electric fishing Effort: Fykes: 2 paired nets for two successive days per site. Winged fyke: one per site for two successive days. Anchor netting: per site 4 surveys of one hour (two for each tide). Electric fishing: only in flood control areas (250 m shore transects/ha).

The dataset contains 69 fish species found in the estuaries of the River Yser and the River Scheldt, as well as 9 non-target crustacean species. The class of Actinopterygii is most represented (67 species), along with two Petromyzontida. All the crustaceans in this dataset are from the order of the Decapoda.

1. Animalia
   common name: animals rank: kingdom
2. Actinopterygii
   common name: ray-finned fishes rank: class
3. Petromyzontida
   rank: class
4. Malacostraca
   rank: class
5. Acipenseridae
   rank: family
6. Agonidae
   rank: family
7. Ammodytidae
   rank: family
8. Anguillidae
   rank: family
9. Atherinidae
   rank: family
10. Blenniidae
    rank: family
11. Callionymidae
    rank: family
12. Carangidae
    rank: family
13. Centrachidae
    rank: family
14. Clupeidae
    rank: family
15. Cottidae
    rank: family
16. Cyprinidae
    rank: family
17. Esocidae
    rank: family
18. Gadidae
    rank: family
19. Gasterosteidae
    rank: family
20. Gobiidae
    rank: family
21. Liparidae
    rank: family
22. Lotidae
    rank: family
23. Moronidae
    rank: family
24. Mugilidae
    rank: family
25. Mullidae
    rank: family
26. Osmeridae
    rank: family
27. Percidae
    rank: family
28. Pholidae
    rank: family
29. Pleuronectidae
    rank: family
30. Salmonidae
    rank: family
31. Scophthalmidae
    rank: family
32. Siluridae
    rank: family
33. Soleidae
    rank: family
34. Syngnathidae
    rank: family
35. Trachinidae
    rank: family
36. Triglidae
    rank: family
37. Zoarcidae
    rank: family
38. Petromyzontidae
    rank: family
39. Cambaridae
    rank: family
40. Cancridae
    rank: family
41. Crangonidae
    rank: family
42. Paguridae
    rank: family
43. Palaemonidae
    rank: family
44. Polybiidae
    rank: family
45. Portunidae
46. Varunidae

Flanders is one of the three administrative regions in the country of Belgium, located in the centre of Western Europe. The Flemish region is situated in the north of the country and covers an area of 13,522 km² (44,29% of Belgium). Belgium has a temperate maritime climate that is influenced by the North Sea and the Atlantic Ocean with substantial precipitation in all seasons. The summers are moderate and the winters are mild. The two main geographical regions of Flanders are the coastal plain in the North-West and the Central plain, further inland. With 470 inhabitants/km², Flanders is one of the most densely populated areas of Europe. The three major rivers are the River Yser, the River Scheldt, and the River Meuse. All rivers in Flanders flow into the North Sea, but only the River Yser drains directly into the sea within the jurisdiction of Flanders. The dataset comprises the estuaries of the River Scheldt, including tidal parts of the rivers Rupel, Durme, Zenne, Dijle and Grote Nete, and the River Yser. The River Scheldt is a 435 km long lowland river originating on the plateau of Saint-Quentin near Gouy, a small town in the French department of Aisne. The river enters Belgium close to Tournai. Then the river turns east, in the direction of Antwerp. After crossing the city of Antwerp, the Scheldt enters the Netherlands where it ends in the North Sea near Vlissingen. The tidal influence extends much further land inward than the freshwater-saltwater boundary. As a result, an extensive freshwater region under tidal influence is present. The tidal activity goes as far as Ghent, 160 km from the river mouth, where the tide is stopped by sluices. In the Zeeschelde (the Belgian part of the estuary), three zones are distinguished following the Venice system (1959): a mesohaline zone (5–18 g salt/kg) between Zandvliet and Antwerp, an oligohaline zone (0.5–5 g salt/kg) between Antwerp and Temse, including the Rupel tributary, and a tidal freshwater zone till Ghent including the Durme tributary. The marshes and mudflats create a valuable landscape for biodiversity. The Scheldt estuary is one of the last natural deltas in Western Europe and many areas near its riverbanks are marked as Natura 2000 areas (Figure 7). Especially its freshwater estuary areas are unique. The River Yser is a 78 km long river originating in Kassel, located in French Flanders. It enters Belgium in the province of West Flanders and drains into the sea near the town of Nieuwpoort. Sea and fresh water meet in an estuary, resulting in 130 hectares of tidal mud flats, salt marshes, dunes, beaches, and polders.