Nimbus Fish Hatchery

The Nimbus Fish Hatchery is located in eastern Sacramento County, built on the left side of the Nimbus Dam.^[1] It is one of the 21 fish hatcheries the California Department of Fish and Wildlife oversees.^[2] Chinook salmon and steelhead are raised, and about 4 million Chinook salmon and 430,000 steelhead released each year.^[3]

History

Salmon once spawned at the head of the rivers of California but with the era of dam building came the loss of spawning ground. Upstream rivers have been damned to control flooding. This has greatly diminished the availability of space appropriate habitat for the fish to spawn and live in. The regional salmon used to migrate up the American river to mountain lakes and now the hatchery is the end of the journey. The hatchery is located along the American River in East Sacramento. The Nimbus Dam cut off historic salmon runs, so in return an artificial system was established. In 1955 the Nimbus Dam was completed. Then, only a year later in 1956 the Folsom dam was completed. This nearly cut off all historic spawning areas. In 1958, the Nimbus hatchery was established to mitigate the impacts the Folsom and Nimbus dams have on the migratory fish, Chinook Salmon and Steelhead Trout, populations in the American River. This was to insure a spawning habitat and to be able to maintain a stable population.^[4] The dam holds sediment and gravels, which change the river habitat below the dam. Gravels needed for historic spawning grounds lead Salmon to look elsewhere to lay their hatch. The Nimbus Fish Hatchery mitigates the loss of upstream habitat.

Nimbus hatchery programs

The hatchery is operated by California Fish and Wildlife, and owned by the Bureau of Reclamation. The purpose is to manage the natural species populations. The hatchery sustains species and gives the opportunity for habitat restoration in the process. Each year over 50 million juveniles are raised in hatcheries and then released to complete their journey down the river.^[5] Funded by the U.S. Congress, the Fish Hatchery programs are focused on seasonal steelhead, Chinook, and Coho salmon. Anadromous Fish hatchers like the Nimbus Hatchery are designed to have minimal impact on natural fish populations. The fall and late fall salmon runs are part of the federal species of concern. As of 1998 ESA listed Steelhead as a threatened species.

Spawning habitat

Wild salmon look for a specific spawning habitat. The size of the gravel influences the survival of their young. The Folsom Dam impacts salmon spawning. Salmon require 7ppm of oxygen to survive in waters. During development small salmon need side pools on the river to get rest in the cool shade and to hide from predators. Salmon eggs are said to need 2-30 centimeters deep water, where drys need anywhere between 20-40 centimeters of water. Salmon need a pH between 6.5 and 8 in waters between 5-8 °C. Thick vegetation along the waters edge provides shade to keep the water cool enough to survive in warmer months. Many spawning habitats have been destroyed or are threatened. Because of this the fish hatchery programs have been put in place to sustain fish populations.^[6]

Impacts on salmon and steelhead

• Number of fish released annually: Salmon (4 million) Steelhead (430,000)
• Number of fish spawned (average): Salmon (2,600) Steelhead (200)
• Number of eggs taken: Salmon (6 million) Steelhead (1-2 million)
• Average number of eggs per female: Salmon (5,200) Steelhead(5,600)
• Average weight at spawning: Salmon(15-35 lbs) Steelhead(6-10 lbs)
• Record weight: Salmon-138 lbs (Alaska) 107 lbs (California) 62.5 lbs (Nimbus) Steelhead-42 lbs (Alaska) 23 lbs (California) 20 lbs (Nimbus)
• Incubation time: Salmon (45 days) Steelhead (35 days)
• Spawning season: Salmon (Oct.- Dec.) Steelhead (Jan. –Mar.)

Figure2. At the Hatchery, one can see the early life stages the salmon undergo while staying at the Hatchery.

Hatchery structure

Figure3. These structures in the middle of the river direct the fish toward the salmon ladder leading to the hatchery during each of the seasonal runs.

The hatchery is part of a greater interconnected network within the region. The dams upstream from the hatchery generate power, supply water, and are a main source of flood control.^[7] As shown in figure 3, the weirs guide salmon in the direction of the ladder to enter the hatchery. The ladder brings them up to harvest and spawning tanks. In November through March the fish Ladder is filled with water to allow for the fish to move up to the ladder. The gates close when the raceway is full, and there is potential for overcrowding. From here workers harvest milk from the adult salmon and fertilize the eggs. There are separate holding tanks for each species, Chinook salmon, steelhead, and rainbow trout. As the fish grow in size they move down the holding tanks. There is a one way gate leading to the holding ponds. The fish then move into a tranquilizing tank on the spawning deck. Only mature salmon are harvested. The holding tanks simulate the natural river flow. The fish jump up the flow to move between tanks. Once the fish grow large enough to survive on their own, between four and six inches, they are carried in tanks further down the river. From here they make their way down stream and eventually journey out to sea.^[8] The hatchery is there to provide adequate space, afterflows, and temperature regimes.^[9]

Contributions

Each year the hatchery raises around 4 million baby salmon. Winter runs of steelhead trout produce nearly 430,000 annually. Fish grow to about 4-6 inches in length at the hatchery before being released into the Sacramento River.^[10] These are grown and released back into the delta. Integrated hatchery programs increase the abundance of species, but are able to minimize genetic divergence in the maintenance of fish populations.^[11] The creation of the Nimbus Hatchery has mitigated for impacts on the steelhead and salmon populations. To measure impacts, the salmon are clipped with a fin clip for analysis if movement, and survival.^[12] Nimbus Fish Hatchery is one of many interconnected Hatcheries in the state of California that are put in place to mitigate impacts on sensitive species. Other Salmon and Steelhead Hatcheries include: Iron Gate Fish Hatchery, Mad River Fish Hatchery, Trinity River Salmon and Steelhead Hatchery, Feather River Fish Hatchery, Warm Springs Fish Hatchery, Silverado Fisheries Base, Merced River Salmon Hatchery, and Mokelune River fish Hatchery.^[13]

Goals

The Nimbus Fish Hatchery was established as part of a greater habitat mitigation network. Currently in the system small Chinook fry from the hatchery are being released lower down river in the American and Sacramento river to avoid predation from larger fish, such as bass. The small fry are often targets of other fish and water fowl in the environmental corridor. A goal of the hatchery is to increase the annual salmon return by releasing closer up river near the hatchery. With this comes a further distance to the ocean, but it may be a safer one. By doing so it would imbed in the hatchery salmon the migratory route to come back to the hatchery from which they came. The Hatchery also plans to find colder water sources for summer runs to minimize the water temperature in regards to the warming climate.^[14] The hatchery is there to provide adequate space, afterflows, and temperature regimes.^[15]

Concerns of Hatchery

The hatchery supplements the natural population but also draws up many concerns on its potential effects. One concern is how the hatchery population relates to the natural population. Main concerns focus on competition, predation, effects of behavior, and potential disease. Due to a varied type of rearing, hatchery fish populations may react to the natural environment differently. They are coming from a controlled environment and entering habitats not only impacted by nature, but societies urban impacts also. In some land locked populations they fight greater for survival. Ever since a small egg first laid in gravel the natural population has had to fight for survival and food. This does give natural populations an advantage to regional familiarity^[16] The hatchery is there to provide adequate space, afterflows, and temperature regimes.^[17] To greater understand the impacts of the hatchery population, monitoring teams need to be put in place. This will allow for special groups to ensure cohabitation without detriment to the naturally occurring population.

Related links

• California Hatchery Program
• Hatchery Review
• California Salmon Spawning^[18]

References