Indicator in the spotlight: Trend of fish in streams and rivers
The indicator ‘Trend of fish in streams and rivers’ tracks the trend in the occurrence of 39 fish species and lampreys in streams and rivers in Flanders. This occurrence is expressed as a percentage: the percentage of measurement locations where a fish species occurs. The trend is based on sampling data from more than 300 locations between 1994 and 2024.
After six sampling periods, we have not observed any major shifts in the composition of fish stocks. However, a number of common species are being caught in more and more locations compared to the early periods. This increase seems to have levelled off in the last period. The number of locations with protected species remains virtually stable. Three-spined stickleback, eel, river gudgeon, roach, and perch are the most common species.
Among the strongest risers are several exotic species. For example, the stone moroko is now found at almost half of all measurement locations. Invasive non-native species can pose a threat to native species, including the European protected bullhead. In recent years, new exotic species such as the monkey goby, the North Asian weatherfish, and the shimofuri goby have also appeared in Flanders.