Rice-sized computer chips help track success of fish passage
June 15th, 2010In April 2008, I wrote about tagging fish with tiny chips and placing downstream fish traps on rivers and streams feeding Lake Billy Chinook for future fish migration studies. Well, the future is now.
PGE’s Megan Hill and her fisheries studies crew have been extremely busy keeping the six downstream-migrant fish traps operating on the Metolius, Deschutes and Crooked rivers and tributary streams feeding Lake Billy Chinook.
All of these downstream-migrant fish traps are designed to capture steelhead and Chinook smolts instinctively moving downstream from natal rearing streams toward Lake Billy Chinook en route to the Pacific.
When captured, smolts are implanted unique computer-chips about the size of a grain of rice. These Passive Integrated Transponders, better known as PIT tags, allow us to recognize individual fish that pass by a “tag reader.” The traps and tags are important tools to study the effectiveness of our new fish facilities.
Addressing the problem: Confusing currents
When Lake Billy Chinook was created by the construction of Round Butte Dam in 1964, it created a barrier to downstream migration because the deep outlet, in combination with the three spring-fed inlet rivers with different temperatures, caused confusing surface currents. Because young salmon and steelhead use surface water currents to guide migration, it was these confusing currents that stopped the anadromous fish runs in the late 1960s.
The new Selective Water Withdrawl facility is designed to correct the problem by pulling the dam’s intake water from the surface instead of the bottom. To assess how it’s performing, we are studying how the water moves through the reservoir and how quickly and successfully the fish migrate to the dam.
Success with trapping and tagging smolts
Though the fish traps in the Metolius and Crooked rivers are sometimes plagued by floods, debris or low water due to irrigation, they have worked well. Megan reports that 899 spring Chinook smolts have been tagged and released at the two traps on the Metolius River. Another 608 spring Chinook smolts have been captured and tagged at the two traps in the Crooked River Basin.
Steelhead are still being tagged in both the Crooked and Deschutes basins, but challenging water conditions have put the trap out of service at Whychus Creek. Steelhead numbers captured at the dam are lagging behind the Chinook, but since steelhead migrate later in the spring and early summer, we expect numbers to increase throughout June and July.
Nearing the goal: 50 percent passage rate
One of the initial goals of the Selective Water Withdrawl facility is to capture at least 50 percent of the smolts of one species (spring Chinook, steelhead or kokanee/sockeye salmon) from one of the three major tributaries to Lake Billy Chinook to demonstrate the new currents support successful fish passage.
Of the 608 Chinook smolts tagged in the Crooked River, 223 (37 percent) had been captured at the new fish transfer facility as of June 7. And we are capturing more tagged fish daily. Although 2010 is a transition year and we expect much improved reservoir passage conditions in 2011, we have a good chance of reaching the 50 percent goal this year with this group of fish.
The capture of 50 percent of one group is a prerequisite set by regulatory agencies before returning adult salmon and steelhead can be passed back upstream. This is because these adults may be harboring parasites and diseases that do not occur upstream. Everyone wants to be relatively certain we have a successful fish passage facility before risking passage of potentially infected adults to waters where these parasites and diseases do not occur now. Achieving a 50 percent passage rate, especially during this transition year, will demonstrate that our facility is working as planned and we’re ready to begin passing adult fish upstream.
- Don Ratliff, PGE senior fish biologist
