Science Friday: Increased flow and spill in the Columbia River is important for more than just smolts

In Science Friday by Nick Chambers


Steelhead in the Upper Columbia and Snake Rivers undergo some of the longest journeys of any anadromous fish — some travel more than 600 miles. Returning adults must navigate numerous dams on their upstream migration to reach spawning grounds. Those offspring that survive to become smolts must make that same migration downstream, past the same dams, in order to reach the ocean.


The Columbia and Snake River dams have fundamentally altered the river’s hydrologic regime. One of the principal consequences of this alteration is reduced migration success and survival for smolts.


Given the threats these dams pose to steelhead smolts (especially summer run fish), considerable research has been conducted to improve understanding of how dam management could be upgraded to better facilitate smolt migration. In general, the results of this research thus far indicate that increased spring flow and spill improve migration rates and increase survival.


The tricky balancing act of trying to operate these dams for power and for the benefit of fish has been contentious. In recent years judges have rejected the federal management plan for the Columbia known as the Biological Opinion (BiOp). Under the BiOp, fisheries managers were directed to increase spill over the dams to aid in the survival of listed salmon and steelhead species until a review of additional alternatives could be completed.


And smolts are not the only life stage of steelhead that need help from dam operators in the Columbia system to out-migrate — steelhead kelts must deal with the same issues. Kelts are post-spawn adult steelhead that attempt to migrate back to the ocean; if successful, they may become the Holy Grail of wild steelhead runs — repeat spawners.

Kelts are rarely photographed as anglers typically, and rightfully, send them on their way quickly, but this girl had her photo quickly taken for educational purposes.


Kelts are an important and, until recently, often overlooked component of wild steelhead populations. Iteroparity, the ability to reproduce more than once, helps increase diversity of steelhead populations and helps buffer them from poor habitat conditions in both fresh and saltwater. Kelts are another vital cog in the wheel of steelhead resilience.


Bonneville Lock and Dam on the Columbia River. Photo US Army Corp of Engineers


Kelts and smolts have two choices when it comes to navigating dams in the Columbia and Snake Rivers. They can either pass downstream using a spillway or through the powerhouse located deeper in the water column.


A 2005 paper by Robert Werthiemer and Allen Evans looked at the survival rates of kelts moving through the Columbia river system on their way to the Pacific. By chance, their two-year study encompassed both a high water and low water year with varying amounts of spill. The researchers concluded that kelts, just like smolts, migrate near the surface and the majority of passage occurs over spillways when possible as opposed to through the deeper power house avenue. While kelts were able to find and use alternative passage facilities, the authors found that survival rates were significantly higher during periods of spill than no spill.


Additionally, migration rates were significantly higher during periods of spill, presumably due to the increase in current. In both years of this study the slowest migration time was in the most heavily impounded reach, and the authors suggested there were strong negative effects of the large reservoirs on downstream travel, and especially so in the Lower Snake River. This is important because kelts have used much of their fat reserves in the course of in-migrating and spawning. Reduced river current places a higher energy demand on the fish because they must actively swim instead of hitching a ride — think of a sailor harnessing the wind compared to the poor chap rowing his canoe across a wind chopped lake. Slower migration combined with low flows means fish will be in the river longer, draining their depleted energy stores and making them more susceptible to factors such as warm water and disease.


Although limited to two years, the data in this study indicate that increasing spill not only helps steelhead pass dams more easily in both directions, but also helps minimize indirect mortality. This seems particularly important in years like this, when runs are predicted to be very low and wild steelhead of all life stages need all the help they can get.


Dams provide relatively clean power and are important to our economy and our society. But so are wild steelhead. Many thousands of anglers, tribes, local communities — all depend on healthy runs of steelhead in the Columbia and Snake Rivers. The Werthiemer et al study’s findings strongly indicate that we should continue to evaluate and refine dam operations to give steelhead the best possible shot at survival.