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Riverine survival
Riverine survival
Problem Statement
Fifty to ninety percent of Snake River yearling and subyearling chinook
salmon die at dams and reservoirs as they migrate downstream to the ocean.
Even when juvenile salmon are barged around hydro-power dams, adult return
rates are less than the rates of return before dam construction.
Critical factors
- Fish mortality at dams and reservoirs impacts rebuilding of sustainable
salmon populations throughout the Columbia River Basin.
- Currently, many juvenile salmon are barged or trucked around the dams.
- Transporting fish around dams seems to increase juvenile rates of survival
but adult rates of return remain lower than expected.
- The relationship between downstream survival rates and adult returns
is unclear.
Status of research
The Northwest Fisheries Science Center (NWFSC) conducts research to
determine accurate juvenile survival rates for Columbia Basin salmon
populations and collects the data needed to compare the survival of
transported and non-transported fish when river flows and spill volumes
increase.
Loading juvenile salmon at Lower Granite Dam
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NWFSC research indicates that juvenile survival through the Snake River
dams and reservoirs is substantially higher than it was during the 1970s when
the lower Snake River dam system was completed. Researchers have collected
juvenile salmon during their downstream migration, implanted transponder
tags (PIT-tags) in them, released them, and detected them at downstream dams.
NWFSC scientists have evaluated the transportation of juvenile salmon
around dams on the Columbia and Snake rivers for more than two decades,
and have found that transported fish survive their downstream journey
at much higher rates than non-transported fish. NWFSC scientists are
currently evaluating survival differences be-tween transported and
non-transported fish when river flows and spill volumes increase. They
collect migrating juveniles at Lower Granite Dam on the Snake River and
mark them with PIT-tags. Some of these juveniles are simply re-released at
the collection site, while others are barged past Bonneville Dam and released
there. The rates at which adult salmon from these two groups return to Lower Granite
Dam are used to evaluate the benefits of transportation. Data indicate that
this benefit appears to vary within the migration season.
Future considerations
Fisheries managers need updated survival estimates for juvenile fish in
order to make rational recommendations for managing hydropower system flow,
spill, turbine operations, and juvenile fish transportation. Additional
research is also required to discover why fish with equally-high juvenile
survival rates have substantially different rates of adult return.
The Center will expand its juvenile survival studies to the entire
Columbia River hydropower system and compare survival rates of transported
and non-transported fish under a variety of environmental conditions.
Key Players
Fish Ecology (FE) Division, NWFSC
Columbia Basin Fish & Wildlife Authority
Columbia River Inter-Tribal Fish Commission
Washington Departmenf of Fish & Wildlife
Oregon Departtment of Fish & Wildlife
Idaho Department of Fish & Game
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National Biological Service, U.S. Geological Survey
Northwest Power Planning Council
Pacific Fishery Management Council
U.S. Army Corps of Engineers
U.S. Fish & Wildlife Service
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Contact: John Ferguson, Director, FE Division (206/860-3270) 
NWFSC Issue Paper FE 6303 (HQ ID 274/275)
Issue Papers Home
last modified 2002-07-29
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