Visbestandopnames op het Dijlekanaal Leuven-Mechelen (2006)

We surveyed 8 locations in the canal Leuven-Mechelen on 2, 3, 4 and 5 October 2006 (Table 1 and Figure 1). 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 distance of 250 m. Furthermore 16 fyke nets were placed along the banks for a period of two to three days. The locations and methodology used are given in table 2.
Abiotic parameters were recorded, they are pH, oxygen concentration, conductivity and temperature (Table 3) and no aberrations were observed. Fish data include species, individual total length and weight (Tables 4 till 8). The Index of Biotic Integrity (IBI) was calculated (Table 9).
In total we caught 5262 specimens (204 kg) and 14 species: brown bullhead, perch, bitterling, roach, stone moroko, Prussian carp, white bream, eel, ruffe, rudd, pike, perch pike, ide and pumpkinseed. Perch, roach, eel, ruffe and ide were found on all site. Species diversity varies between 6 and 10 with an average of 7.9 per site. The piscivores consist of pike perch, perch and some pike specimens. The perch population shows all characteristics of a dwarf population most probably because of food competition with roach. Compared with results obtained during previous campaigns (1996 and 2001-2002) the fish assemblage remains quite stable. The same species remain dominant: perch followed by roach and eel. More species were caught during previous surveys but in 2001-2002 the sampling was very intensive and in 1996 more site were sampled.
The IBI values are slightly better in 2006 than in 1996.
If fish stocking is still considered than we suggest to stock one year old pike individuals to reduce the amount of perch and roach specimens.