The National Marine Fisheries Service released four draft white papers from its Northwest Fisheries Science Center on aspects of salmon survival through the Columbia/Snake River hydropower system that it says will provide scientific background for the upcoming NMFS 1999 biological opinion.
NMFS will take comments on the studies until Oct. 29, and after that the papers will influence both the 1999 BiOp and the way the Columbia River power system will operate in the coming years.
The studies look at passage of both juveniles and adults past the dams, the relationship of survival to flow and time, transportation of juveniles around Snake River dams and predation. A summary of each of the report's conclusions follows:
"Passage of Juvenile and Adult Salmonids Past Columbia River and Snake River Dam" - (link is no longer active)
For juvenile salmon:
- Survival is better today than it was in the 1960s and 1970s, with these caveats: better survival occurs in those years with good flow conditions and with the measures suggested in the 1995 and 1998 BiOps. However, there is evidence that traveling through multiple dams reduces the smolt to adult return (SAR) ratio.
- Survival is highest through spillbays, followed by mechanical screen bypass and turbines.
- Spill survival is 98 percent to 100 percent, except at The Dalles Dam, where, since 1997, it's ranged from 76 percent to 99 percent.
- Screen bypass works without much harm to fish. Survival is higher than through turbines, except at the Bonneville Dam (one test only).
- Although stress in a fish can rise while traveling through bypass facilities, stress levels generally return to normal within several hours. But, during that time, it could contribute to a limited ability to respond to some in-river conditions, such as predators.
- Other findings are that scaling could be a problem when debris is present and high temperature at McNary kills fish.
- Further testing and improvements to bypass facilities are required.
For adult salmon:
- Limited information about adult spring and summer chinook survival between Ice Harbor Dam and spawning grounds or hatcheries indicate there may be little difference between survival now and before the dams were in place. However, low survival in 1991 and 1993 requires further investigation.
- Fallback rates at lower dams are high and should be addressed through more research.
- It is uncertain whether migrating through a series of dams affects reproductive success.
"Salmonid Travel Time and Survival Related to Flow Management in the Columbia River Basin"
- (link is no longer active)
- There is a stronger flow to travel time relationship for fish that migrate in the spring than those that migrate during the summer.
- Fall chinook juveniles from the Hells Canyon section of the Snake River begin their migration 4 to 6 weeks later than before the dams were in place. Warmer water in the fall and cooler water in the spring delays adult spawning in the fall and juvenile emergence in the spring. Outflows from Brownlee Dam that would more closely approximate historical temperatures could affect this timing and improve survival.
- Higher flow may result in better survival downstream from the hydropower system, such as in the estuary.
- SARs are lower when flows fall below 85,000 cubic feet per second in the Snake River, 135 kcfs in the mid-Columbia River and 200 kcfs in the lower Columbia River.
- The hydropower system affects the Columbia River estuary, pointing out the need to manage flows "toward a more natural spring hydrograph."
- Flow management is providing benefits to smolt survival, but they are difficult to quantify.
- Impoundments create delays in travel time which flow management cannot entirely correct.
- Downstream migrants continue to suffer high mortality. Therefore, additional flow augmentation to benefit Snake River fall chinook would increase the likelihood of survival.
"Summary of Research Related to Transportation of Juvenile Anadromous Salmonids Around Snake River and Columbia River Dams"
- In most studies, fish that were barged or trucked through the lower Snake River dams survived better than in-river fish.
- Over 90 percent of transported fish are barged.
- One test of yearling chinook on the Snake River found that trucked fish return 5.8 times better than in-river, while barged fish return at a rate 8.9 times more, but the researcher suggested more tests should be done because another study of steelhead and fall chinook showed no significant difference.
- The potential for delayed transport mortality will require further study.
- In-river juvenile hatchery chinook migrate faster than barged hatchery fish, and they travel in tighter groups.
- Straying is no more a problem with barged fish as with in-river fish and there is no evidence that increased straying of steelhead into the Deschutes River is a result of barging.
- Nearly every part of barging, from handling and collection, to mixing wild and hatchery fish, to release causes stress.
- There is uncertainty about levels of post-transport and post-bypass mortality that should be evaluated.
"Predation on Salmonids Relative to the Columbia River Power System"
- Dams and their reservoirs increase predation on salmon.
- Conditions in reservoirs favor introduced competitors. Passage conditions at dams can increase exposure time of juveniles to predators.
- The most important fish predators are northern pikeminnow (dominant predator below the Snake River), smallmouth bass (dominant predator in lower Snake River) and walleye.
- Recent estimates of pikeminnow predation in the Columbia and Snake river basins extrapolated from a John Day reservoir study predict that 16.4 million, or 8 percent, of juveniles are eaten by pikeminnowannually. Smallmouth bass and walleye each eat an estimated 1.4 million juveniles.
- Predator control of the pikeminnow has resulted in a reduction in predation of 13 percent.
- Basin-wide losses to avian predation "constitute a substantial proportion of the juvenile salmonid outmigration."
- Principle avian predators are Caspian terns, double-crested cormorants and several species of gulls.
- Terns eat 6.4 to 24.7 million salmon smolts every year in the Columbia River estuary. Most are hatchery fish, but about 100,00 to 600,000 are wild fish.
- Predation by marine mammals is not a large factor and is largely unknown, but can be a factor locally when adult salmon runs are low or at obstructions, such as dams or fish passage facilities.
NMFS Northwest Home Page:
Northwest Fisheries Science Center
All White Papers are posted in PDF format.
Predation on Salmonids Relative to the Federal Columbia River Power System
Salmonid Travel Time and Survival Related to Flow Management in the Columbia River Basin
Summary...Transportation of Juvenile and Anadromous Salmonids around Snake and Columbia River Dams
Passage of Juvenile and Adult Salmonids Past Columbia and Snake River Dams
NMFS Releases Draft White Papers
Columbia Basin Bulletin, October 15, 1999
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