Salmon imprint on their home using magnetism and scent as they swim downstream to the ocean. Years later, this imprint guides anadromous fish back to where they hatched as they travel inland from the ocean to their spawning grounds. Their arduous journey against strong currents and rapids can cover hundreds of miles up many thousand feet in elevation. Traditional salmon survived the upstream migration for millennia but humans have added obstacles. Contemporary salmon living in a human-dominated landscape might begin life in hatcheries and travel to the ocean in trucks, thus missing the chance to learn the imprint of home. Biologists wonder how many trucked salmon will swim upstream and find natural spawning grounds or reach the hatcheries. In the past few years, this question was especially pertinent when drought conditions meant all hatchery salmon migrated inside the steel climate-controlled tank trucks.
Salmon have been evicted from their historic homes and lifestyles as we dammed major rivers, cleared riparian habitats, built levees to control flooding, and diverted water for agriculture. In California, dams block access to 90 percent of salmon spawning habitat. To compensate, wildlife officials truck about half of the Sacramento River basin hatchery salmon to the ocean in a normal year. The other hatchery-spawned salmon are released to migrate down rivers to the ocean.
But the ability to successfully migrate requires adequate water flows and suitable water temperatures. The recent drought in California, diminished habitat conditions making downstream migration dangerous or impossible. For two years all the salmon raised each year — 30 million Chinook salmon — traveled by truck from Sacramento River basin hatcheries to the ocean.
Does iron in the steel fish tanks or electrical cables in hatcheries disrupt salmon’s magnetic GPS system? How many of them will be able to find their way home? How do they define home when they began in a hatchery tank and migrated in a truck? What do hatchery salmon sense when they dream of home?
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Salmon brought us good news at the end of 2016 when high numbers of chinook salmon arrived in the natural spawning grounds of Putah Creek. The good news relates not only an increase in salmon, but also our abundant fall rains and restoration of the creek’s ecosystems.
Putah Creek begins high on Cobb Mountain in the Coast Ranges northeast of San Francisco and extends about 85 miles to the Sacramento River (at the Yolo Bypass), then into the Sacramento-San Joaquin River Delta, and finally the Pacific Ocean. Sixty years ago, 90 percent of the creek’s watershed (576 square miles) was impounded by Monticello Dam to form Lake Berryessa and provide irrigation water for adjacent downstream counties. European settlers began the process in the late 1800’s and by the late 1900’s nearly all hydrology, geology and vegetation of Putah Creek’s historical condition had changed.
Decades of habitat destruction created stagnant water and other conditions inhospitable to salmon. Monticello and smaller dams held back gravel sediment that forms loose beds in which salmon lay their eggs. Water diversion limited flows. Channel straightening, levees, mining, and riparian vegetation removal destroyed shade, extensive flood plains, and shallow riffle spawning grounds.
The Putah Creek Diversion Dam in the lower portion of the creek diverted water to UC Davis and Solano County Water Agency (SCWA)
Lower Putah Creek, which once supported over 22,000 acres of lush riparian forest, has been modified over the years into a regulated stream following an unnatural channel….
During the summers of 1989-90 nearly 23 miles of the creek below the diversion dam was dry, in part due to a seven year drought but also because flows were not required from upstream dams. Cottonwood and willow trees, tadpoles, fish, crustaceans and other life died. Beaver dams and lodges were abandoned in dried mud.
In the early 1990’s negotiations began between conservation groups and SCWA to increase minimum flows in the creek below the Diversion Dam although adequate terms of water releases to support fisheries weren’t finalized until 1999-2000. The agreement was credited when “a record number of 70 salmon nests” was documented in the creek in 2004. In 2013 during another drought, however, only eight salmon were found.
This year 1,000 to 1,600 chinook salmon are spawning in Putah Creek. The new record high salmon run is thought to be due to increased flows, habitat restoration efforts and, oddly, California’s recent drought that forced CDFW to truck all salmon from the hatcheries to the Delta for the ocean phase of their lives. The normal watercourses these salmon would have used to reach the ocean were too dry or warm for the past few years. At least a quarter of this year’s salmon in Putah Creek are thought to be trucked hatchery fish. A portion of hatchery salmon have a small tag inserted into their nose that identifies the hatchery, river system, and release strategy. After spawning, biologists collect the tags and track how many salmon returned to spawn and where they ended up.
“Most places in the Central Valley, the numbers are down,” said Peter Moyle, a distinguished professor of wildlife, fish and conservation biology at UC Davis. “The fact that we’re getting a new run is a positive sign.” [...]
As the fish travel back to their spawning grounds from the Pacific Ocean, they might be able to find the right river, but the exact tributary they were born in isn’t clear to them. Most fish end up settling in a place that looks like good habitat, and this year, Putah Creek appears to fit the bill.
Putah Creek Council began restoration efforts in the mid 1990’s to improve habitat for native fisheries, including features aquatic invertebrates need to reproduce. The Army Corps of Engineers had removed much of the riparian vegetation until the late 1950s, resulting in bare creek banks that eroded easily and were colonized by exotic invasive plants such as Himalayan blackberry, arundo, eucalyptus, and tree-of-heaven. Many of these plants don't lose their leaves in winter and thus don't respond to rain and storm flows the way deciduous native plants do. Native riparian vegetation is flexible and bows over during high water flows while the non-natives are rigid. This traps sediment and causes erosion as flow is diverted onto the creek's banks.
Streamside restoration also provides better habitat for terrestrial insects, birds and mammals. Bird populations have doubled since the 1990’s. Minks and bobcats are seen more often in the riparian habitat. At least 25 species of reptiles and amphibians, 40 species of mammals (plus 11 bats) and 114 species of birds have been documented in the area. As Putah Creek is restored, it becomes a good home for salmon.
What they need for their full life cycle is returning to the creek. The water flow and stream quality will be suitable for salmon if we have enough rain and manage upstream releases properly. Putah is supporting the aquatic invertebrates and smaller fish that salmon eat at the beginning of their lives. It provides the clean, cool waters shaded by riparian trees needed for migration, and stream beds with just the right size sedimentary gravels salmon require for spawning at the end of their lives.
No matter where they hatched, anadromous salmon now can dream of swimming to Putah Creek. They won’t need to Uber home.
Watch 2014 salmon truckin’ down the valley from hatcheries to begin their ocean life.
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