A fascinating article, with profound implications, from the California Water Blog.
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.
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.
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.