Local salmon struggle to survive

Folsom and Nimbus dams wiped out sensitive habitat and Nimbus Hatchery tries to compensate

(Bottom to top) Andy Heape, Ron Desilva, Justin Mather and Jason Rodgers trim the adipose fin off fry to mark them as hatchery fish.

(Bottom to top) Andy Heape, Ron Desilva, Justin Mather and Jason Rodgers trim the adipose fin off fry to mark them as hatchery fish.

SN&R Photo By Anne Stokes

Join Jennifer Davidson tonight for a discussion on artificial spawning at Nimbus Hatchery on 90.3 FM, KDVS’ Radio Parallax, between 5 and 6 p.m. or listen to the podcast at www.radioparallax.com under “Shows.”

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Eight miles of the American River stretching between Ancil Hoffman Park in Carmichael and the Nimbus Dam in Rancho Cordova are all that remain of a once robust 125 miles of Chinook salmon spawning habitat in the Central Valley.

Although California’s salmon populations have declined since early settlers colonized the region 150 years ago, nothing has had a greater impact on the species than the construction of the Folsom and Nimbus dams.

In the 1940s, Congress identified the untamed spirit of the Sacramento River as a flood hazard to the region and ordered the U.S. Bureau of Reclamation to dam the river and regulate its flow. The dams were designed to complement a growing population’s infrastructure with flood control, energy generation, drinking water for nearly 1 million people and a culture of aquatic recreation that is a signature of our region, said Jeff McCracken of the Bureau of Reclamation. However, the salmon would lose more than 100 miles of precious habitat in the deal.

To compensate for the habitat loss and the direct impact on the species, the Bureau of Reclamation provided funds to build and operate the Nimbus Hatchery, built in 1955 at the time of Folsom Dam’s completion, to artificially spawn and raise Chinook salmon to propagate declining wild species, McCracken explained. As part of its mitigation, the Bureau of Reclamation is required to meet minimum flow levels in the American River, as well as water quality criteria and regulation of temperature for salmon populations. The bureau works with the California Department of Fish and Game to implement these requirements.

“The dam allows us to keep the American River flow up by releasing excess water into the river when it gets extremely low during the dry season,” McCracken said. Minimum flow levels stimulate salmon to migrate and help maintain clean spawning grounds and overall water quality by washing away pollutants and sediment.

For cold-water species such as salmon, temperature is imperative to its reproductive cycle. Five years ago, the Bureau of Reclamation installed a device to allow cold water to be withdrawn from the bottom of the reservoir and released into the river to meet temperature requirements for salmon migration, McCracken explained. Though this year, salmon ready to spawn returned to Nimbus Hatchery later than usual due to warmer river temperatures.

In November, the river temperature reached the required 61 degrees Fahrenheit for spawning and the first fascinating, but brutal, egg-take and fertilization of the season finally took place at the hatchery. In a little less than one year, these newly fertilized pea-sized, bright orange eggs will be among 32 million, 6-inch salmon smolt raised at the hatchery and ready for release.

Nimbus Fish Hatchery fry.

SN&R Photo By Anne Stokes

As part of the management strategy, some of the smolt are released into the American River at the hatchery, while the majority of the 32 million are trucked and released at key locations in the Delta and Bay Area, close to the Pacific Ocean, explained Harry Morse, Public Information Officer for the California Department of Fish and Game.

“This reduces the in-river mortality rate of the smolt and ensures that most of the fish will make it to the ocean,” he said. A smolt’s journey downstream is the most perilous leg of a salmon’s life. The staggeringly low rate of salmon that return to the hatchery to spawn makes this management strategy imperative to propagate the species as efficiently as possible.

“We see less than 1 percent and sometimes less than one-half of 1 percent return rate,” Morse said. On the low end, that’s fewer than 160,000 fish out of 32 million that are genetically pre-determined to return to Nimbus Hatchery.

Solving the mystery of salmon’s declining numbers challenges even the best Ph.D.s in the field, according to Morse. Loss of habitat due to dam construction poses the greatest threat, though biologists target sedimentation, altered stream flow, loss of streamside vegetation, rise in water temperature and pollution—all the result of human activity—as the categorical biggies that account for dozens of complex threats to the species.

The Department of Fish and Game will soon undertake a major project to tag a quarter of the salmon raised and released at the hatchery to track where they go and how many survive to help biologists understand what is happening to the hatchery stock, Morse explained.

While the conundrum has captured the attention of the scientific community, there is still plenty the average citizen can do. One of the easiest methods to protect the health of salmon and waterways is to prevent pollution through storm drains, which empty directly into rivers without receiving treatment. Animal and green waste, trash, motor oil, detergent from washing cars and residual pesticides from lawns are typical storm drain pollutants.

“A pollutant itself may not directly kill a salmon,” Morse said, “but it can destroy or affect small invertebrates and plant life,” which in turn impacts the food supply and alters the landscape of sensitive salmon habitat.

Most importantly, Morse pointed out that to save the salmon, we must generate a collective voice that understands the needs of the species and recognizes its value as a natural resource with historical and cultural importance, and a species that deserves its place on the planet.

Salmon are arriving at the hatchery daily, completing their journey from the Pacific Ocean and ready to spawn. Come face to face with these magnificent creatures and watch them make their way up the ladder into the hatchery. The Nimbus Hatchery is located near Hazel Avenue and Highway 50, off Gold Country Boulevard and is open from 10 a.m. to 3 p.m. daily. Call (916) 358-2820 for more information.