When Steelhead Go Too Far

11/25/2014  By Alex Conley - YBFWRB
When we wrote the 2009 Yakima Steelhead Recovery Plan, NOAA planners assumed that 90% or more of our steelhead made it up the Columbia and directly into their home tributaries. Since then, more steelhead are being implanted with Passive Integrated Transponder (PIT) tags. These electronic tags are a little bigger than a grain of rice. When a tagged fish swims past a detector, the tag number is recorded. With all the new data coming from these detectors, we’re realizing that the assumptions about adult migrations that were made back in 2009 were rather simplistic.

On November 19, fisheries managers and recovery planners from throughout the Mid-Columbia and Snake Basins met in Walla Walla to share this new data and the surprising conclusions that it is leading us to. So what did we learn? The short answer is that adult steelhead movements are anything but simple.

It is clear that steelhead from the Yakima- and other rivers- like to dip into the Deschutes and the Klickitat on their way up the Columbia, no doubt to cool down in the water draining straight off the high Cascades.  Just about all of these fish move back out and head up the Columbia towards home. This means that fisheries managers in these popular rivers need to remember that many of the fish that are caught in them may not be from these rivers at all!

More surprisingly, many steelhead make it to the mouths of their home rivers (as determined by where they were tagged as juveniles) and then keep on going further up the Columbia and Snake Rivers. Fish from the Yakima pass four big dams in the Columbia to get home, and PIT-tags show us that some keep going past as many as four more dams, almost all the way to Canada- and then turn around to come back to the Yakima! Some fish that overshoot never do make it home.

In some areas, this overshooting is clearly having a negative impact. The John Day River in Oregon is probably the most extreme case. There, over 50% of the tagged adult steelhead go up the Columbia past McNary Dam, which is 70 miles upstream of the mouth of the John Day River. 40% of those fish are never detected making it back to the John Day. They may be harmed coming downstream through dam turbines, or caught in fisheries, or simply die after the long migration. Add in the fish that never make it up to the John Day, and the reduction in the numbers of adults spawning in the John Day is dramatic.

The Tucannon River is an example of a more complicated situation. Based on PIT-tag data, only 40-50% of the steelhead that enter the Snake actually make it home to the Tucannon- and almost half the run goes up the Snake way past the Tucannon and never makes it back down. This is a lot like what is happening on the John Day. At the same time, of the fish that do make it into the Tucannon, as many as 40% of the wild fish may be strays from other populations, like the John Day and Umatilla. What does it mean for meeting recovery goals when a population is both losing fish, and gaining strays from elsewhere? If the abundance goal is 500 wild fish, does it matter where they came from?

So what happens in the Yakima? Pretty much any PIT-tagged fish that comes up the fish ladder at Chandler Dam in Prosser is detected by the antennas mounted there, so we’ve got good data. We do see about 15% overshoot- with most headed up the Columbia towards Wenatchee, and a few going past Ice Harbor Dam on the Snake River- but at least 2/3 of our overshoots are making it back to Prosser. Only 5% don’t make it back, and we appear to get few strays from elsewhere. While we don’t have the same big issue with overshoot that other parts of the Mid-Columbia do, we need to remember that for our Yakima steelhead to be delisted, all other parts of the Mid-Columbia also need to be ready to delist- and that may not happen until we figure out how to respond to the overshot issue.

So why do fish overshoot, and what can we do about it? It’s generally assumed that they are looking for appropriate holding habitat, to rest in and wait for the best conditions to migrate up their home rivers, but that they are not finding it, either in the warm and highly altered lower ends of their home rivers, or in the big reservoirs that now make up most of the mainstem Columbia River. It’s likely at least some of this wandering would have occurred before the dams went in, but it is now they have to pass through the dams when they try to move back downstream to home. That makes the #1 priority figuring out how to pass adult fish downstream in the fall through early spring- a season when spill, bypass and sluiceway operations are limited. Mainstem managers are conducting research on how best to do this, with the least impact to hydropower generation. We’ve already seen real successes in improving downstream passage for kelts (post-spawn steelhead) later in the spring, so chances are good that real solutions can be found.

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