Visbestandopnames op de bovenschelde

The INBO, Provincial Fisheries Committee East-Flanders, the Provincial Centre for Environmental Research East-Landers and the ANB East-Landers, surveyed 36 locations of the River Bovenschelde between 29 Mai and first of June (Table 1 and Map). Fish assemblage data were obtained by electric fishing from a boat using a 5 kW generator (DEKA 7000) with an adjustable output voltage ranging from 300 to 500 V. The pulse frequency is 480 Hz. Electric fishing was carried out along both banks over a variable distance. In some locations we also placed fyke nets for one or two days. The locations and methodology used are given in table 2.
Abiotic parameters were recorded, they are pH, oxygen concentration (DO), conductivity and water temperature (Table3). Fish data include species, individual total length and weight (Tables 4 till 7). The Index of Biotic Integrity (IBI) was calculated for this and previous campaigns (1996, 2002, 2006) (Table 8).
During this campaign 19 different fish species were collected: three- and nine-spined stickleback, brown bullhead, perch, brown trout, gibel carp, carp, white bream, bitterling, roach, stone moroko, bream, eel, ruffe, rudd, gudgeon, pike perch, belica and tench. The most common species was roach which is present in 16 locations. We collected fish in 22 sites and the species diversity ranged between one and 13 (5.2 average).
Two main observations were made:

1. electric fishing seems to be inefficient in this type of river (lower catches than fykes)
2. the ecological quality for the locations in the part between Pottes and Oudenaarde is obviously worse than that in the stretch between Oudenaarde and Gent.

In 1996 the ecological quality in the River Bovenschelde was generally bad (Table 8). In 2002 we observed an important increase in the ecological quality. However, in 2006 apparently a decrease in ecological quality is recorded, but the lower catch effort may be also a result of the abnormaly dry en cold weather of the spring of 2006.