Here, we briefly go through things that are important to consider when creating spawning sites and spawning beds. In this field support, we focus on the species trout, grayling, and salmon. In the training section of this webpage, you can deepen your knowledge about creating spawning sites and spawning beds.
Water Depth and Velocity
The water depth should be between 0.1 and 0.7 meters, and the water velocity should be between 0.2 and 0.9 meters per second. The optimal water velocity is between 0.2 and 0.5 meters per second. Keep in mind that the water velocity can change relatively easily when you add spawning material. Also consider the current flow. If it is low, the velocity may become too high at higher flows, and vice versa.
Size
The size of the spawning bed naturally varies depending on the size of the fish that will spawn there. For example, for stationary trout, a rule of thumb is 0.5 to 1 square meter, and for salmon, it is 1 to 4 square meters.
Appearance and Thickness
Spawning beds are almost exclusively constructed with a slope, becoming shallower the further downstream you go. The thickness of the spawning bed should be at least 30 centimeters, but preferably up to 50 centimeters. If the spawning bed is sloped, it is easier to achieve water flow with oxygen-rich water, which is crucial for the survival and development of the eggs.
Site Selection
Choosing the right location is very important. Factors to consider include:
- Keep in mind that a high flow can wash away a spawning bed if the water velocity becomes too high. Therefore, try to choose a site where the watercourse does not become narrower, causing the water velocity to increase at higher flows. The site should allow the water to rise without increasing velocity. Good locations include downstream from pools or stretches of the watercourse with low confinement and floodplain areas.
- Choose a site that will not become too shallow or even dry out, or experience excessively low water velocities during lower flows.
- Position spawning beds near good rearing areas. Avoid placing them just upstream of hard rapids or pools that are unsuitable as rearing habitats.
Protection and Structures
It is beneficial to have areas where the spawning fish can feel safe near the spawning site. These could include deep pools, boulders, dead wood, or overhanging riparian vegetation. It is also a good idea to enclose spawning beds with stones to prevent competition between individuals, which is especially useful if you have several spawning beds near one another.
Barriers and Support
The most common method is to use a natural or artificial riffle neck to hold the gravel in place during high flows. Start by digging out a depression upstream of the riffle neck where you plan to place the spawning gravel. Be sure to dig deep enough so that the spawning bed is not too shallow when you add the material. Fill the area with spawning material and ensure you create a sloping bed that is properly supported. You can now check the flow and depth, making adjustments to achieve the best possible conditions.
