Life Cycle and Habitat Needs

Coast coho salmon (Oncorhynchus kisutch), also referred to as silver salmon, spawn in tributary streams and rear in the rivers, streams, lakes, and estuaries that drain into the Pacific Ocean along the Oregon coastline. The river systems that support Oregon Coast coho flow from the rain-drenched coniferous forests of the Coast and Cascade mountain ranges, while rivers that support Oregon’s populations of Southern Oregon Northern California Coast coho rise in the Klamath-Siskiyou ranges to the south.

Since coast coho salmon spend up to half of their lives in freshwater, the quality and quantity of winter and summer rearing habitats is critical to their productivity and survival. Illustration by Elizabeth Morales.

Coho normally begin life in small tributaries. After emerging from the gravel, the fry seek cool, slow-moving off-channel habitats, such as backwater pools, beaver ponds, and side channels. The “standard” coast coho life history type generally spends one summer and one winter in natal tributaries before migrating into the mainstem rivers and eventually into low-salinity reaches in the estuaries. There they slowly acclimate to saltwater before moving to the ocean. (Other life history strategies may move more rapidly into mainstems, non-natal tributaries, and estuaries). Off the Oregon coast, the fish are strongly influenced by ocean conditions, especially by the timing and intensity of upwelling, a process in which near-shore ocean currents bring cool, nutrient-rich water from the ocean floor, stimulating food production for coho and other salmonids.

Coast coho salmon rely on a variety of different habitat types during the freshwater portion of their life cycle. These habitats are generated and maintained by a dynamic, inter-connected system of watershed “components”. When the watershed processes that connect these components are broken or impaired, habitat degradation or loss ensues. The Strategic Action Plans focus on repairing these processes, so each component can generate the high quality habitats necessary to sustain coho. CLICK on the titles above for definitions of these components.

Several watershed characteristics – or key ecological attributes (KEAs) as they are called ─ such as habitat complexity, riparian function, water quality, and floodplain connectivity are used to define healthy freshwater and estuarine habitats that are essential to supporting a viable coho population.

Complex stream habitat is particularly important for winter survival of juvenile coastal coho because it provides shelter from predators and high winter flows, which can prematurely flush juveniles downstream. It is also important during summer months when high water temperatures can threaten the fitness and survival of juvenile salmon. Similar conditions support coho survival and productivity during their stay in the estuaries. Habitat conditions that create sufficient complexity for juvenile rearing and overwintering include large wood, pools, connections to side channels and off-channel alcoves, beaver ponds, lakes and wetlands.

These habitats (and the benefits they provide) are maintained through watershed processes that connect them to the surrounding landscape, especially riparian areas, hydrologically connected wetlands, and upland stands of timber that deliver pulses of large wood and gravel. Beavers are particularly important to coho in creating critical off-channel rearing habitats. In addition to creating high quality physical habitats, beaver colonies also drive essential watershed process that sort gravel, filter sediments, and maintain cold water and base flows in summer. Finally, the unimpeded movement of coho between stream reaches and off-channel habitats is essential.