The chart above illustrates dramatic rises and drops in California’s Central Valley salmon population over the years. Survival of California’s iconic salmon, as well as the $1.4 billion salmon industry, which supports 23,000 jobs in most coastal communities in Northern California, is in serious danger of collapse.
Because salmon are anadramous (they live part of their lives in fresh water, part in the ocean), they show us strong signs of the health or damage to both freshwater and marine environments. When dams were built, Central Valley salmon lost about 80 to 90 percent of their historic spawning habitat. They also lost very valuable rearing habitat in side channels and former floodplains.
All of these rivers in California used to produce salmon. Now only parts of a few do
Every major Central Valley river was dammed with none being fitted with a fish ladder
At the same time Central Valley salmon rivers were largely straightening and river banks were armored with heavy rock, or diked and leveed, mostly to create more farmland. This denied baby salmon access to the banks, edges, side channels, and floodplains where they’d historically found rich feeding grounds and safe refuge to hide from predators.
Miles of river banks have been straightened and armored with rock denying baby salmon places to feed and shelter
Today, dams capture and stop much of the spring rain and snow runoff needed to carry baby salmon from the Central Valley to the ocean. Only in the wettest years, when reservoir operators are forced to release water to prevent over topping of dams, is there the type of spring runoff baby salmon evolved to take advantage of. (It’s interesting to note that after years of litigation to bring salmon back to the Columbia and Snake Rivers in WA, OR and Idaho, a federal judge finally granted salmon advocates one wish. What they chose was to release water from upstream reservoirs in the spring to aid the downriver out migration of the baby salmon every year and runs there have rebounded as a result.)
Gone too is the natural turbidity created by sediment suspended in runoff that provides natural camouflage that baby salmon need to hide from roving predator fish and birds.
Instead, all too often during spring, rivers run slow and clear and baby salmon become easy prey for predators.
Dams and water diversions in our rivers give a heavy advantage to predators that eat baby salmon
One of the biggest problems for today’s Central Valley salmon are the mammoth water diversions in the Delta. Both of California’s Central Valley major rivers, the Sacramento and San Joaquin, meet in one large Delta some 60 miles east of the Golden Gate Bridge. Decades ago the state made a decision to tap the Delta waters and export them south to southern California cities and to dry desert lands in the western San Joaquin Valley for agricultural use. This decision was made with no thought about the harm this would do to salmon.
A series of massive pumps are strong enough to make the San Joaquin River run backwards
Top graphic shows natural out migration route for baby Central Valley salmon. Big fish icons near state and federal pumps represent predators that eat baby salmon.
Second graphic depicts how baby Central Valley salmon are pulled off their natural migration course when the state and federal Delta pumps are turned on. When this happens, most are lost to predators in interior Delta.
The National Marine Fisheries Service (NMFS) recognizes the pumps as salmon killers and has required restrictions on pumping to minimize damage to winter and spring run salmon, both protected under the federal Endangered Species Act. NMFS estimates that as much of 90 percent of baby salmon pulled off their natural migratory route to the bay and ocean are lost to predators in the interior Delta or when pulled into the pumps. Put differently, for every baby salmon captured at the pumps, nine other likely died from the effects of the pumps.
Of the fish captured at the pumps, most are dumped back into the Delta at locations where predatory fish have become accustomed to feeding. Changes in the river bottom throughout the Delta leaves deep scour holes where predators congregate and feast on baby salmon. Other problems beset Central Valley salmon.
In today’s Central Valley salmon try to spawn in rivers that are often too hot to successfully incubate fertilized eggs. River temperatures above 56 degrees kill incubating salmon eggs.
Salmon eggs die when river temperatures exceed 56 degrees
Starting in September and historically peaking in mid-October, fall run salmon lay eggs in nests (called redds). The redds are often left high and dry and eggs killed when water managers drastically cut reservoir releases later in the fall when agricultural demand for water is over for the year.
Massive water diversion intake pipes dot Central Valley rivers. They suck in untold numbers of baby salmon, some of which wind up deposited in agriculture fields as part of irrigation water. In recent years this problem has been recognized with the bigger diversions now screened to avoid this loss. But many smaller unscreened diversions still exist and are easy to spot all along the Central Valley rivers.
Human development and competition for the water from Central Valley rivers has been no friend to salmon. But they persist in spite of the all the environmental destruction around them. There are things we can do to make it better.