What lies behind the dam? In some cases, self-sustaining salmon


A juvenile Chinook Salmon, about 9 cm FL, from the Tuolumne River above New Don Pedro Reservoir, May 18, 2012. (Perales et al. 2015)

By K. Martin Perales

Chinook salmon are a remarkably adaptable species. There is good reason to believe there are multiple populations of landlocked Chinook salmon completing their entire life cycle above Central Valley dams. We recently documented spawning above six of thirteen reservoirs that have been stocked with Chinook. In some cases, populations have persisted for several years after stocking of juvenile salmon has stopped, suggesting self-sustaining populations.

The stocked salmon are juveniles that have been stocked by the California Department of Fish and Wildlife (CDFW) to be harvested by recreational anglers. These fish seem to be using the reservoir as a surrogate for the ocean. It is likely that the stocked juvenile salmon feed in the open water and grow into adults in the reservoir. Individuals that avoided being harvested and have matured into adults can go on to reproduce in historic spawning streams and rivers, now inaccessible to anadromous fish because of dams.


Dams block about 90% of critical habitat for salmon. Map courtesy of NOAA.

What do these populations mean for anadromous salmon? For one, they serve as a reminder that above reservoirs, quality spawning and rearing habitat exists. These are streams where anadromous Chinook salmon have been absent for many years – in some cases, over a 100 years. Some estimate that dams block about 90% of spawning habitat in the Central Valley. This habitat loss, along with other changes in the landscape, has been implicated in the decline of salmon. Restoring access to this lost habitat will hopefully address a key limitation in the life cycle of salmon and other migratory fish. The current spawning activity shows that despite being isolated for so long, the habitat is still good for salmon. This validates the idea that we should increase habitat connectivity somehow.

These landlocked Chinook salmon may be a roadblock to increasing habitat connectivity. Most of these planted fish are not native to the rivers below the reservoirs in which they are stocked. Instead, they are ‘surplus’ juveniles from Iron Gate Hatchery, located on the Klamath River, outside of the Central Valley. The presence of these out-of-basin fish spawning above Central Valley reservoirs may complicate our ability to restore native salmon above the dams. Klamath River fish are genetically distinguishable from all fish in the Central Valley, including those that are below the dams where the Klamath River fish are reproducing. Mixing out-of-basin and local salmon will lead to reduced genetic diversity, which makes populations less resilient. Thus, we should avoid mixing these populations to maintain whatever is left of the genetic integrity of these runs.

Shasta Dam

The McCloud River is located above Shasta Dam which stands 602 feet high. Photo courtesy of the Bureau of Reclamation.

What now? I am not sure. We have regionally native fish that have been transplanted to streams they are not native to, and are living in an ecosystem that has never existed until recently. Their effect on the restoration of native populations is unknown, but may be detrimental. Should we get rid of these fish to facilitate future restoration efforts? Perhaps a two way trap and haul program (moving adults above and juveniles below a reservoir), such as is proposed for the McCloud River above Shasta Dam will be more viable with them gone. It’s possible that we’ve already taken steps to eliminate these unique populations. CDFW recently switched over to planting sterile triploid fish in some of the reservoirs. We shall see whether the landlocked Chinook populations will continue to self-sustain.

However, even if the populations eventually die out, we have few good options to get the desired local native salmon above our huge dams. Many of our dams are too tall for ladders. Fish elevators are inefficient. Some remain skeptical of trap and haul as a long term solution. If we can’t retrofit dams with ladders and can’t move fish easily, are we only left with removing dams as an option, as has been proposed for the Klamath River?

On the other hand, our study raises an interesting question. What if an endangered or threatened run of Chinook salmon, such as winter or spring run, were established above a dam and used the reservoir like an ocean? Can this population act as an acceptable refuge population? Could this population supplement existing runs? There are many examples of ‘feral’ self-sustaining populations of landlocked Chinook salmon around the world; why not rear some threatened varieties from California in our own reservoirs? And sure, it would be a compromise to have landlocked varieties over wild salmon. Everything is a compromise compared to the historic runs California used to sustain. It’s possible that by changing our concept of how we want salmon to persist, we may have discovered a new aid in their recovery.

K. Martin Perales worked with Dr. Peter Moyle as an undergraduate investigating relationships among water quality, slough morphology, and hydrodynamics and their effect on fish communities of the North Delta. He is currently earning his PhD at the University of Wisconsin – Madison studying human impacts on lake fish communities.

Further Reading

Perales et al. 2015. Evidence of landlocked Chinook salmon populations in California.

National Oceanic and Atmospheric Administration. 2014. Central Valley Chinook salmon & steelhead recovery plan.

Shindler et al. 2010. Population diversity and the portfolio effect in an exploited species.

Waples et al. 2004. Life-history divergence in Chinook salmon: Historic contingency and parallel evoluvtion.

Noonan et al. 2012. A quantitative assessment of fish passage efficiency.

California Trout. 2015. Officials consider trucking salmon above Shasta Dam.

This entry was posted in Biology, Conservation, Fish, Salmon and tagged . Bookmark the permalink.

4 Responses to What lies behind the dam? In some cases, self-sustaining salmon

  1. gymnosperm says:

    “CDFW recently switched over to planting sterile triploid fish in some of the reservoirs. We shall see whether the landlocked Chinook populations will continue to self-sustain.”

    Wow. In chillier periods ice has created dams. Yosemite Valley was an ice dam lake. Huge areas of Western North America were once covered by “landlocked” ice dam lakes. Species of trout evolved behind them.

    My suggestion is to embrace the change and quit trying to pretend that we can ever know what the “one true” salmon genome for a watershed is.

  2. Nicholas Clark says:

    “Klamath River fish are genetically distinguishable from all fish in the Central Valley…Mixing out-of-basin and local salmon will lead to reduced genetic diversity.”

    To me, it seems like there is a step in the process of reducing genetic diversity that is being left out here. Can somebody explain how introducing two genetically distinct populations to each other that could presumably sexually reproduce will lead to diminished genetic diversity?

  3. pacific flyway says:

    We can conclude there are four salmon runs in California each year. Winter, Spring, Summer & Fall — four. In other words, salmon are running all year round everywhere in California. Anyone with the fee can buy a salmon fishing license in California. A license to kill a so-called
    ‘endangered species’. More than 80% of the water now diverted from the Sacramento
    River passes through state-of-the-art fish screens so that salmon stay ‘safe’ in
    the rivers. Farm drains are fitted with outfall gates so that salmon don’t take detours and get
    ‘lost or stranded’ in canals. All water not taken-up by wetlands, crops, plants
    and trees returns to the river and the environment, or percolates down
    recharging groundwater aquafers. The water gets used again & again downstream by
    multiple species and cities. The striped bass and the black bass are voracious
    predators of salmon smolts. California has restrictions limiting how many can be caught. Striped bass are a non-native introduced fish prized by sport fishermen. Sport fishermen join-in with environmental lawyers to help file lawsuits on behalf of billionaire donors who seek to seize control over the water distribution system in California for profit. Peer-review science one on side of the debate lend credibility and create an echo-chamber. Water fines and
    settlement payments collected from farmers for ‘violations’ are handed directly
    over to environmental justice organizations which help rail against the 1% farmland owners in harmony with the sport fishermen & science community. 1% Wall Street titans okay – 1% farmers not okay.The goal is to hand control of California’s water distribution system, and the money we pay for it, over to an elite class of non-elected billionaires who can raise
    prices on water with impunity – turning water into gold. Over 200,000 tons of gravel has been reintroduced into the Sacramento River for spawning habitat. Farmers & taxpayers continue to spend more & more on environmental enhancements to protect salmon to please an increasingly
    hostile electorate. Sport fishermen spend on boats, bait, beer & gear. Billionaires make super PAC contributions and tax-deductible donations to environmental organizations to employ armies of tax-deductible of lawyers to advance their pursuit of more power and personal wealth.

  4. Pingback: Training Scientists to Be Better Science Communicators | UW-Madison Center for Limnology

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