Idaho fall Chinook recorded slowest Columbia–Snake dam passage since PIT tagging began

There were high hopes for the Chinook salmon season in Idaho. But then unseasonably high water temperatures disrupted the expected migrations along the Columbia and Snake River basins. 

The number of adult salmon that passed the Bonneville Dam was counted at around 36,000. This is way short of the 47,000 noted in the preseason forecast. The fish making their way through the dam system are moving at the slowest pace ever recorded, according to electronic PIT tags. The projected survival rate in the river has now dropped to 48 percent, and urgent fishery management solutions have been activated. 

How raised water temperatures mean slow upstream migration

Adult salmon have been tracked with integrated transponder tags. This data shows that they are choosing to stay put in cooler pockets of water rather than brave the discomfort of moving upstream through warmer channels. This means the Chinook trying to return for the fall have to use up their energy reserves while they wait for cooler currents to pass through.

In previous slow migration years, overall survival between Bonneville Dam and Lower Granite Dam hovered around 50 percent. Current mathematical projections indicate an even steeper decline down to 48 percent, meaning only 24,000 adult fall Chinook will reach Lower Granite Dam—well below the ten-year average of 34,000 fish.

The wild adult fish return count is sitting at around 4,700. This is the lowest wild return rate in the state since 2009. Slower migration speeds have an effect on the count of healthy spawning adults, with fewer reaching the upper tributaries of the Snake River. 

Adaptive management is urgently needed for wild run protection

There is a flexible sliding scale put in place by state and federal authorities to protect naturally spawned fish. This governs wild salmon mortality. It is a management framework that ties the impacts of allowed catches to the total number of wild adults that pass over the Lower Granite Dam.

When the wild returning fish number is above 5,040, sport fishing activities may catch up to 10 percent. If this is maintained, no mid-season rule changes are imposed. However, a drop below this threshold means an automatic drop in allowed harvesting to six percent.

The latest wild fish count projection is sitting at 4,700. Fishery managers are under a restriction on unclipped, natural salmon. State officials have decided that all wild adult Chinook salmon must be returned to the water as soon as possible after hooking and with minimal harm. But they are allowing hatchery-bred salmon to be kept (identified by clipped adipose fins). This way, conservation mandates can be met while recreational angling along the Snake River can continue. 

Hatchery propagation is the most viable option for population maintenance

Artificial salmon breeding is essential to maintain population baseline levels, and these programs are already in place along the Columbia River and Snake River system. There are three regional hatcheries in operation that, together, produce 5.65 million juvenile Chinook smolts for release each year. Of these, 80 percent are placed above Lower Granite Dam. Facility operators have production targets to fulfill, so they use specialized traps along fish ladders to collect the broodstock returning upriver with as little stress as possible.

Ongoing environmental tracking is needed for long-term salmon resilience

There are jurisdictional rules that apply to anglers on the boundary between Idaho and Washington. Some anglers have licenses for both states, but they can only fish under the privileges of one of those states at a time. Fish that they want to retain must be landed on shore, and only then may they switch permits. The anglers also have to know how to tell the difference between Chinook salmon on their return trip from other species like coho, wild steelhead, and protected sockeye salmon.

The vulnerability of wild salmon migrations to raised water temperatures is open to environmental stress, according to the Idaho Fish and Game Commission. The reductions in wild returns require immediate restrictions on fishing of unclipped salmon.