redds

Redds are nests formed by female salmonids during spawning in gravel substrates of rivers and streams. The nest, or redd, is excavated by the female using her tail and fins to create a shallow depression and an underground egg chamber beneath the stream bed; eggs are deposited in the chamber and then covered with gravel to protect them from currents and predators.

Redds are typically located in clean, well-oxygenated gravel in moderately fast-flowing water, often at riffle-pool transitions. Substrate size is important; gravels ranging from coarse gravel to small cobble are common, while excessive fines can reduce oxygen flow and harm developing embryos. The exact shape and size of a redd vary by species and site.

Many salmon and trout species construct redds, including Pacific salmon (Oncorhynchus spp.), Atlantic salmon (Salmo salar), brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis), and other salmonids. Spawning timing is species-specific; in temperate regions, it commonly occurs in fall or winter, with eggs incubating through winter and hatching in spring. Incubation duration depends on water temperature and species.

Redds are used as indicators of spawning habitat quality and salmonid population status. Biologists conduct redd surveys to estimate abundance and distribution and to monitor habitat changes. Redds are vulnerable to habitat disturbance such as sedimentation, gravel removal, and altered flow regimes, which can reduce oxygen delivery to eggs and increase post-spawn mortality. Restoration efforts may involve protecting spawning grounds, reducing sediment input, and gravel augmentation to restore suitable redd substrates.