Between fall and spring, spawning grounds are full of salmon redds, gravel nests dug by spawning females, containing thousands of eggs, (which develop into alevins). The redd protects eggs and alevins from predators and from washing away in heavy stream flows, but being well hidden on the ground makes them susceptible to unwitting trampling by people, pets and livestock.
How bad is it if you step on a redd and how can you avoid it?
Limited data has been collected on the impact of human activity on salmon redds. However, studies on trout redds show that trampling can cause mortality rates between 43 – 96 per cent. A similar rate applied to wild salmon redds could be disastrous, especially for endangered populations.
Though trampling of redds isn’t a large cause of the decline of wild salmon, it is one of the few threats that we can easily remedy with a bit of awareness.
Here are some tips for identifying and avoiding salmon redds.
Be especially vigilant for salmon redds between September and March in most locations in B.C.
Do you see adult salmon?
If you visit a waterway and adult salmon are present, it is likely a spawning stream. Keep out of the river and keep pets on leashes to prevent damage to redds.
Know where redds are found in a stream
- Pools vs. riffles. Pools occur where stream depth increases and flow decreases. Riffles are shallower sections of the waterway where the water moves more quickly. Riffles are preferred locations for salmon redds as the increased flow of water helps keep the redd well-oxygenated for baby salmon.
- Substrate. Salmon redds are made in gravel 15- 35 mm in diameter (pea to peach pit size). It needs to be small enough for the females to be able to move it and create their nest, but large enough that it doesn’t smother the eggs by getting too densely packed.
- Location. Be more vigilant when walking in or through the middle of a stream. Salmon often spawn close to the centre of streams, not close to the banks.
- Water depth. Most salmon spawn in relatively shallow water of a few feet or less.
What does a redd look like?
- Look for clean gravel. The act of creating a redd involves the female salmon disturbing gravel, which makes the circular area of about 1-2 m in diameter that has cleaner looking gravel than the surrounding area.
- Look for a combination of a mound and a depression in the gravel. The mound, where the eggs are located, will be downstream of the depression.