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SONCC Coho salmon are identical in appearance to Central California Coast Coho, and are distinguishable only by genetic differences.

About 75 years ago, between 100,000 to 300,000 SONCC Coho returned to spawn in freshwater each year. Currently, populations are less than 5% of historical abundance, or less than a generous estimate of 5,000 wild individuals. The number of streams capable of supporting Coho salmon runs have declined 40-50%. Accurate abundance estimates covering a large timespan are uncommon, which makes population trend analysis difficult.

Virtually all female and most male SONCC Coho salmon in California are three years old when they spawn, with some males returning as two year-old “jacks.” Spawning migrations begin in September through late-December in Northern California, with a peak in October-November, while spawning occurs mostly in November and December. In some years, spawning can occur as late as March in some watersheds, especially if stream flows are low or access is limited because of drought. Females deposit 1,400-7,000 eggs. Eggs hatch in early spring, and alevins slowly absorb their yolk sac before seeking out prey. Unlike most other salmonids, juvenile SONCC Coho salmon use parts of their spawning streams and estuary habitats throughout the year. These young salmon require very cold, clean water between 10-15.5°C (50-60°F) to grow. In the spring-fed Shasta River in Northern California, juvenile SONCC Coho salmon can flourish in warmer waters of 18°-20°C (66°-68°F) because food is abundant and habitat conditions are favorable. Juveniles generally feed and grow in slow-moving, off-channel habitats, small, clear tributaries, and estuaries before undertaking ocean migrations in the spring. They generally express three life history strategies: 1) juveniles up to one year of age feed and grow in their natal streams and migrate to sea in the spring; 2) juveniles up to two years old feed and grow in estuaries and off-channel habitat during winter and spring before migrating to sea during the first major fall rainstorm; and 3) yearling juveniles move downstream to other streams or estuaries in spring and grow in the main channels during summer and fall before migrating in the winter. Once at sea, Coho from different regions school together as they migrate to the North Pacific to feed on small fish, shrimp, crabs, and invertebrates before returning to spawn after 6-18 months.

In California, Punta Gorda (Humboldt County) separates California’s two Evolutionary Significant Units (ESUs) of Coho salmon: SONCC Coho and Central California Coast (CCC) Coho salmon. Coho have strong homing instincts to their natal rivers, and so populations from neighboring streams are closely related to one another. Historical widespread stocking of non-CCC Coho salmon has not appeared to reduce the genetic integrity of remaining wild fish.