Fish migration
Fish are present in virtually every body of water. The presence or absence of certain species can say something about the functioning of the ecosystem. For example, species such as tench and rudd prefer to live in clear water with aquatic plants. Bream and carp are less picky. Some species live in both fresh and salt water, depending on their life stage.
For many fish, it is important that they can move freely through the water system. This allows them to travel to different areas, for example to search for food or to reproduce in shallow ditches. Or to survive a harsh winter in the deeper parts of a polder. Fish are generally very good at finding their way. However, some species depend on other water systems for their life cycle. The presence of pumping stations, locks, and weirs has made life difficult for these species. A well-known example is the eel, which swims all the way from our waters to the Sargasso Sea (near Cuba) to reproduce. By constructing fish passages at the transitions between water systems, we are trying to restore the so-called migration routes. When constructing new pumping stations, we use fish-safe pumps that allow around 95% of all fish to pass through alive.
Monitoring with volunteers
Research programs involving volunteers are being conducted along both the North Sea Canal and the Wadden Sea coast. Using a cross net, small groups monitor migration hubs for the presence of migratory fish, such as eel and three-spined stickleback. More information about this can be found at: Fish - Cross-net monitoring (Ravon.nl). Various research reports can also be found here.
Fish stocks
The fish population in an area is determined by environmental conditions. In a canal in a nutrient-rich clay area, you will see different species and often more fish than in a ditch with a sandy bottom near the dunes. Fishing activities also have an impact, of course. Fish are sometimes caught for consumption, or species are introduced, for example, if they have disappeared from a water system.
In the Hollands Noorderkwartier Fish Stock Management Committee, we make agreements with fishermen about fish stocks. The starting point for this is the water quality targets asprogramme in theprogramme .
We periodically have the fish stocks in the water bodies examined. The corresponding reports are stored in the Hydrotheek. Use the search term 'Fish stocks HHNK' followed by the name of the water body.