The federal agency that regulates water releases from the Shasta Dam in Northern California drastically cut those releases in November, and one fisheries group is afraid that the move could have killed millions of eggs laid by fall-run chinook salmon in the Sacramento River below the dam.
According to the Golden Gate Salmon Association (GGSA), the U.S. Bureau of Reclamation (BuRec) cut releases from Lake Shasta from 6,000 cubic feet per second (CFS) to 3,750 CFS between November 1 and 25. This caused river levels downstream to drop dramatically, which means that any salmon eggs laid in parts of the river that died up will almost certainly be lost.
This isn't the first year BuRec has cut November water releases from the dam, and those cuts have hurt salmon in previous years. As many as 15 percent of the Sacramento river's fall-run eggs were lost after a similar move in 2012, and almost a quarter of the run's 2011 eggs were killed the same way, according to GGSA.
Like other Pacific salmon, the Sacramento's fall-run chinook salmon (Oncorhynchus tshawytscha) re-enter the streams in which they're born at the ends of their adult lives to spawn. When they reach a suitable spawning ground, the females prepare patches of suitable gravel in which to lay their eggs with sweeps of their powerful tails. The gravel patches, called "redds," provide the eggs some protection from the elements and predators while allowing sufficient water circulation to keep the eggs oxygenated. Once the eggs are laid in the redds, male salmon fertilize them with a cloud of what fisheries biologists call "milt."
The fertilized eggs hatch out after 90-120 days, depending on the temperature of the water. The hatchlings, called "alevin," may then remain in the gravel beds for three or even four months, gaining additional protection from predators and living off the contents of egg sacs attached to their bellies when they hatch.
It's not until the alevins completely consume their egg sac contents that they emerge from the gravel, swim to the surface to gulp some air into their swim bladders, and do their best to survive in the open water of their natal stream. Until that time, which may be several months after spawning, the young salmon have no way to survive if their redds dry out.
"Once salmon have laid their eggs in the river, it's up to water managers to keep them safely under water until they hatch," GGSA Executive Director John McManus said in a press release. (Full disclosure: John and I are former co-workers.)
McManus and GGSA had attempted to negotiate with BuRec to curtail water releases earlier in the season. If that suggestion had been carried out, fall run salmon would have been less likely to lay eggs in redds that would later dry up.
BuRec likely cut the releases from the dam because the San Joaquin Valley growing season had come to an end for the year. The less water BuRec releases from Lake Shasta during the off-season, the more water will be in the lake at the beginning of the next season to water Kern County cotton.
"Killing the offspring of naturally spawning salmon is what you don't want to do if your goal is to reduce reliance on hatchery fish and rebuild wild runs," said McManus. "It's hard to rebuild natural runs when water releases are managed this way."
The fall run of Sacramento River chinook salmon needs rebuilding, though numbers have climbed since a near-catastrophic failure of the 2007 run prompted the Paciﬁc Fishery Management Council to prohibit commercial and sport fishing of chinook south of Portland, Oregon for two years. Unlike the Sacramento winter-run and Central Valley spring run, fall run chinook in the Sacramento River aren't protected under the Endangered Species Act. However, NOAA Fisheries does monitor the fall run as a "species of concern," a semi-formal status in which the agency places populations it fears are at risk of becoming endangered.
If the number of young fish returning to the ocean is hammered by a loss of eggs in Sacramento River redds, another closure could well result, potentially putting thousands of people out of work and threatening the welfare of the $1.4 billion California salmon fishing industry, not to mention the salmon themselves.