Report on Harmonisation of freshwater biological methods

In non-wadable or large rivers, the main sampling season is also in autumn, but alsoin the summer in the Danube.Belgium – Flanders134. The fish population surveys are standardised both for wadable and nonwadablerivers. The principal method of fish sampling is electric fishing, but othermethods such as gillnets, seine netting or fyke nets are also used in large rivers, and insome specific water systems (e.g. in Polder drainage systems).135. In wadable rivers, the number of electric fishing devices and the number ofanodes are dependent on river width, from 1 anode for river width smaller than 1.5 mto 4 anodes for rivers of 6-8 m wide. Electric fishing is performed in an upstreamdirection. At each station (sampled area = 100 m long), a maximum of 200 specimensof each species are individually weighed and measured). Captures by fyke nets, seinenetting and/or gill nets are sometimes used to complement the electric fishingcaptures, principally in standing waters (channels).Belgium – Wallonia136. Despite the absence of a regular fish-monitoring programme defined at theregional level, several institutions (Universities, public administration responsible ofnatural resource management) perform frequent fish sampling operations in Wallonia.Electric fishing is used by all institutions, with relatively similar, but not standardised,sampling procedure. In addition, fish capture data obtained with gill nets, seinenetting, fake nets or fish pass control are also compiled in the regional fish database.137. In rivers, electric fishing is performed over a distance of 150-350 m,regardless of river width, with 1-3 passages depending on sampling objectives andinstitutions. Stop nets are used as far as possible, but if the water flow is too high orthe river too wide, sampling areas are selected in such a way that natural barriers(small weirs or very shallow riffles) delimit the prospected zones. The preferredsampling seasons are summer and autumn.138. In non-wadable rivers, electric fishing and horizontal bottom gill nettechniques are combined. Electric fishing is performed from a boat, in an upstream ordownstream direction along both banks, by a staff of 4 persons including the anodeoperator. Both electric fishing and gill netting are usually performed during daylight,97