Remote Site Incubation: An Alternative Method for Rearing the Endangered Central California Coast Coho Salmon in the Russian River Watershed

While serving as a GrizzlyCorps Fellow at Gold Ridge Resource Conservation District, I’ve had the amazing opportunity to work with the endangered California Central Coast (CCC) Coho Salmon. These fish are ecologically critical because they are highly sensitive to even small changes in their environment. As an indicator species, Coho helps us assess ecosystem health. When their numbers decline, it signals that something is out of balance. Coho require specific conditions to thrive, including adequate streamflow, cool water temperatures, high dissolved oxygen levels, and appropriate stream habitat.

The Coho Salmon life cycle begins in winter when the female lays eggs in her nest, called a redd. She turns on her side and uses her caudal fin to dig into the stream gravel, creating a divot for the eggs. Once she lays her eggs, she covers them with gravel and protects them until she dies. Her carcass releases nutrients back into the ecosystem. Once the eggs hatch, they become alevin, which means their yolk sac is attached to their bodies so they can feed off it. Over a few weeks, the yolk sac is absorbed, and the young fish are called fry. By the following spring, they will become smolts as they migrate to the ocean. They feed on shrimp and small fish, remaining in the ocean until they return to their natal streams as 2 (jacks) or 3-year-old adults to spawn.

Eggs Stage.

Alevin Stage

Coho Salmon in the Russian River are part of the Central California Coast Evolutionarily Significant Unit (ESU), meaning their population is genetically unique from other coho salmon along the Pacific Coast. In 2005, CCC Coho Salmon were listed as endangered, prompting the creation of the Russian River Coho Salmon Captive Broodstock Program (or RRCSCBP for short). The RRCSCBP raises CCC Coho Salmon to adulthood, spawns them, and releases their offspring throughout the Russian River watershed. At the Don Clausen Warm Springs Fish Hatchery, the Army Corps of Engineers (ACOE) uses a genetic matrix to spawn Coho Salmon. Each fish is spawned with a predetermined partner to maximize genetic diversity of the population. The program’s primary goal is to reestablish a self-sustaining population.

Remote Site Incubator set-up.

Remote Site Incubators (RSIs) are an alternative rearing and release method, allowing fish to develop in remote stream environments at an early age. Fertilized eggs are transferred from the hatchery to the incubator a few days before they are expected to hatch. The eggs hatch in the RSI, and the fish develop for about a month before being released into the stream. There are many potential benefits to using RSIs as a recovery tool. RSIs likely improve behavioral development and physical fitness of the fish and enable the hatchery to release more fish each year. The fish can adjust to the stream’s water properties at a young age, which improves the chances of coming back to the same watershed as an adult to spawn.

Thanks to permitting and project guidance from the NOAA Fisheries, California Department of Fish & Wildlife, and ACOE, Coho eggs were raised in a RSI this past winter. We collaborated with CA State Parks to install the RSI in a tributary of the Russian River. Meeting with the ACOE staff, we carefully transported the eggs into the RSI, using aerated backpacks. We looked a little funny hiking up the hills with the backpacks, carefully trying not to cause too much movement for the fish. During the operation, the tiny eggs hatched, growing from alevin to fry; they were quite excited to start swimming in their creek. The coho fry were released in the tributary, where Trout Unlimited will be assisting with post-release monitoring and data analysis.

The outcomes for the 2025 RSI operations are as follows:

The 78.23% egg-to-fry survival rate is considered high and aligns with the survival rates seen in the Don Clausen Conservation Hatchery. These results suggest that RSIs can be used as an additional release strategy due to their effectiveness in raising eggs to fry without taking up space and resources at the hatchery.

Crew walking to the site, looking sort of like Ghostbusters!

This method is still relatively new and depends largely on the site characteristics to plan appropriately. As this approach is repeated, it will become easier to understand the nuances of certain environments and how to best approach them. Working with an endangered species has been incredibly rewarding, and I am grateful to have this rare opportunity.