Rushing Water PIT Tag

Scientists conduct a spill test of the embedded PIT tag antennas at Lower Granite Dam.

Although new PIT-tag antennas were installed in December in only one spillbay at one of eight dams on the lower Columbia and Snake rivers, scientists say the data being gathered from the effort will be very helpful.

The new data, which started rolling in during the spring from fish going over the spillway at Lower Granite Dam, will make current estimates more accurate and enable new studies that couldn't be done without this new system in place.

Funded by BPA and the U.S. Army Corps of Engineers, the 11 PIT-tag readers embedded in the concrete spillbay in three arrays (CU No. 1933 [14]) were operating beyond expectations in the spring. It's the first-ever PIT-tag detection system to be installed in a high-velocity spillway, and is powerful enough to capture electronic signals through seven inches of concrete from the rice-sized tags implanted in salmon, steelhead and other fish dropping over the dam at 70 feet per second.

The $7 million system began operating in early April, and by June 25 it identified more than 153,000 juvenile salmon and steelhead that had spilled over the dam on their migratory journey to the ocean.

This total includes 75,498 Chinook, 64,971 steelhead, 10,384 sockeye and 2,470 coho. Without it, scientists would have detected slightly more than 33,000 salmon and steelhead that have gone through the dam's juvenile bypass system, and would have to assume that the rest either didn't make it to the dam, or passed over the spillway.

Throughout the Columbia Basin, more than 1 million fish are fitted with PIT tags each year. They can be tracked when they pass by any of about 250 detection sites, and their information is kept in the PTAGIS database, funded by BPA and administered by the Pacific States Marine Fisheries Commission.

PTAGIS has been operating as a regional database of information on fish marked with PIT tags for 25 years, marking the journeys of some of the 33 million tagged fish through about 150 million detections.

But as spill has increased over the eight lower dams in the Snake and Columbia rivers, the number of juveniles detected through their bypass systems has decreased. Ben Sanford, a data analyst for NOAA Fisheries, said that this spring, with higher levels of spill than ever before, scientists would be scratching their heads without the new data from Lower Granite Dam's spillway.

"The spill program has drawn a lot more fish away from the bypasses and turbines, so the detection rates at all the other dams is lower than usual," he told Clearing Up. "It's really low."

And with fewer detections, he noted, scientists have to make more assumptions.

Sanford said environmental conditions in the Snake and Columbia rivers are already so dynamic that when you add in changing operations at hydroelectric projects and how fish respond, there are a lot of variables for scientists to consider.

"When we don't have lots of data, it can be very hard to learn things," he said. The new detection system at Lower Granite is a huge gain in absolute detection—a 500 percent increase, he noted.

Sanford said when looking at the survival rates of fish tagged and released above the dam, and their survival rates to Lower Granite Dam, the standard errors were 10 times lower when combined with data from the detections over the spillway.

"The estimates were pretty similar—the mean survival—but the standard error is much smaller," he said. That will change with different water years, or different spill programs, he noted, adding, "But in a year like this year, the timing of having that system come on line was fantastic for those of us who work in this."

And, there are many other uses for the data besides survival rates. Scientists can start comparing fish that pass through the spillway with those that pass through the bypass system in the same time period, Sanford said. They can start to test some of the assumptions made about juvenile fish that travel past dams through the different routes.

"We've been asking those questions for years," he said.

They can also get a better understanding of the fallback issue—when adult salmon or steelhead are migrating upstream, and fall back to the tailrace of a dam after making it through the fish ladder. "Now, we actually have the information on those that fall back," he said. "It's just one little piece, but it's the kind of data you can get" with the new detection system.

In general, Sanford summarized, "More data is better, and different data is informative."

Dave Swank, fish biologist for the U.S. Fish and Wildlife Service, and a member of the Columbia River Technical Management Team, agreed. "Certainly, anything we can do to increase the sample size is helpful," he said.

Swank said the most obvious initial use for the new data is estimating the survival rates of fish released above Lower Granite Dam.

"Biologists try to estimate how many of the fish released from a hatchery made it downstream to Lower Granite before starting to make their way through the FCRPS system. We want to know what the starting survival rate is," he said.

With a background in steelhead biology, Swank said he's struck by the number of adult steelhead already detected going over the spillway. Unlike salmon, steelhead have the ability to go back to the ocean and then make the arduous journey back upstream to spawn again. Those repeat spawners are called kelt.

"This is showing a lot more kelts out there than some people realized," he said, adding, "This will start to fill in the picture of what's going on with steelhead kelts."

He said he also expects to see bull trout, both sub-adults and adults, which can travel upstream and downstream.

With a new set of data, Swank said it's also important to keep in mind what not to expect from it. "The limitation is that it's only at Lower Granite, and it's only in one spillbay, and it's only detecting PIT-tagged fish," he noted. That means more hatchery fish will be counted compared to wild fish, although not all hatchery fish are marked with PIT tags, either.

The Fish Passage Center outlined some of the differences between detections from the new system with a passage index in an April 24 memo.

"It's not going to be a perfect representation of the juvenile run-at-large," Swank said, but added, "It is still very useful, I think."

He said the new detection system is also a big deal because it's the first detection over a spillway at any of the Federal Columbia River Power System dams.

"It was a big technical challenge for the Corps and NOAA to build it," he said, and the success marks an important technological advancement. Scientists are already talking about where they'd like to see the next spillway detection system installed, he said.

"We're probably to the point of still figuring out how best to use the data," Swank said. "It's a whole new data source, so it'll take us a little while to really dig into it and figure out what it's telling us. I'm personally excited about what it's telling us already."

K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.