Visbestandopnames op enkele waterlopen gelegen in de Brugse polders

In Total we surveyed 27 sites spread over 18 water courses situated in the basin of the Brugse Polders (Table 1, Figure 1). We were assisted by the provincial fishery commission of West- Vlaanderen and the Agency for Forestry and Nature. On 6, 7 and 8 April fish assemblage data were obtained by electric fishing from a boat or wading using a 5 kW generator (DEKA 7000) with an adjustable output voltage ranging from 300 to 500 V. The pulse frequency is 480 Hz. The locations and methodology used are given in table 2.
Abiotic parameters were recorded, they are pH, oxygen concentration (DO), conductivity, temperature and stream velocity (Table3). Fish data for different surveys (2002, 2003 and 2006) include species, individual total length and weight (Tables 4 till 7). The Index of Biotic Integrity (IBI) was calculated for this and previous campaigns (2002 and 2006) (Table 8). In total 14 species were caught: three-spined stickleback, nine-spined stickleback, perch, roach, stone moroko, bream, gibel carp, carp, white bream, eel, rudd, pike, stone loach and tench. In 2002 the same species were collected and in addition chub, ide and belica.
In general we observe that most sites have a poor ecological status. Compared to 2002 the number of dead sites (no fish) halved and fish densities increased in 14 sites. Six sites decreased in status from moderate to poor. Only one site in the Bornebeek scores good. In a fair amount of the sites we discovered a thick mud layer. This does not improve chances to obtain a sustainable and diverse fish population. Though the presence of a good structure and a varied vegetation indicates that there is a potential to obtain a good status for these rivers.