Amber Moore of Puget Sound Partnership, who funneled money to King County for this project as part of the National Estuary Program, says people paying for these restoration efforts need to know they’re investing in jobs that have the greatest likelihood of success and that their money is being carefully invested. This proof will attract more money for this work.

That’s why Gregersen and a team are implementing this study to explore two questions: Are the fish even using the lower Green River or are they just crossing it? If they stick around, what section of the river do they spend their time in?

Why are you chasing fish like this now?

The new technology Gregersen is testing in beta for King County allows these questions to be asked pending useful answers – a relatively new phenomenon due to the historical limitations of tracking fish.

Researchers have been injecting adult fish with electronic tags for years. These labels, the size and shape of a Good & Plenty candy, require very little maintenance. Unlike Tile trackers that you would use to find your keys, these trackers use radio frequency identification, or RFID, technology that you would find in a credit card. They don’t need batteries and can stay in a salmon’s body for its entire life without the need for updates.

Scientists follow tagged fish by installing sensors along rivers: when fish pass a few meters from them, sensors detect tags and read their data. This is a huge improvement over traditional tracking methods. In the past, some scientists injected fish with tags that had to be extracted and read manually. Others colored the fish with ultraviolet paint. For both techniques, the researchers had to collect fish again after releasing them, says “which is absolutely impossible,” says Gregersen.

To inject a mark into a fish, environmentalists first place it in anesthesia baths like the one Gregersen installed at the Icy Creek Hatchery. Environmentalists then load what looks like a child-sized glue gun with a tag and carefully inject it into a salmon towards its tail fins. It is a delicate process.

“The more they eat, the softer they get – to the point where you start pushing and pushing, and then if it pops, obviously the needle might prick something you don’t want. So this spring we had to put our hatchery fish aside and not feed them for several days, ”says Gregersen, fish in hand.

The problem with earlier versions of RFID tagging technology was that the fish in this study – the juveniles – are small, around 2 inches when they start swimming downstream. Two could easily fit on your cell phone. Neither has much internal space for tracking devices. So when King County discovered new rice size labels, it jumped on them.

The labels are encapsulated in glass, making them inert, and the process leaves a small incision that heals within days. The fish wakes up after about a minute. The mortality rate is one in 1,000 fish, and so far no fish have lost their tags.

Gregersen started tagging in March, about a month after juveniles appeared in river systems, and has so far equipped at least 1,000 wild-caught juveniles and 3,000 hatchery fish with the technology.

The beacons are associated with a 4000 pound floating detection barge, designed by West Fork Environmental and attached with strong cables to the Southcenter pedestrian bridge. Eventually, the fish tagged today at Icy Creek will overtake it.

This barge has been tested a few times in eastern Washington, but never before in the Puget Sound area.

Umatilla Indian Reservation Confederate Tribe Fisheries Biologist Travis Olsen says the use of barge technology from 2019 has had a big impact on the tribes’ ability to track fish, including trout BC summer rainbow and spring chinook. This allowed them to follow in deeper water towards the mouth of the Walla Walla River, with fewer repair issues than they would have with things like anchored sensors.

In total, the King County project is worth $ 300,000.

Preliminary results of fish monitoring

So far, says Gregersen, preliminary data has been promising, revealing things about fish activity that we didn’t know before, including that detected fish stay in the Lower Green for two to 63 days, the smallest fish remaining the longest.

It was huge, says Gregersen: “Until now, we didn’t even know if the fish were using this highly modified habitat.

Research suggests that small fish need off-channel habitat, such as small tributaries, which can be refuges during high river flows. Fewer of these places exist in urban rivers. Built banks prevent erosion, but reduce the nooks and crannies where juveniles can rest and feed, and barriers make it difficult to enter and exit quieter tributaries.