Amber Moore of Puget Sound Partnership, which funneled money to King County for this project through the National Estuary Program, says the people paying for these restoration efforts need to know they are investing in work that has the highest likelihood of success and that their money is being carefully invested. This evidence will attract more money for this work.
And so Gregersen and a team are implementing this study to explore two questions: Are fish even using the Lower Green River or just passing through it? If they do stick around, in which section of the river do they spend their time?
Why track fish like this now?
New technology that Gregersen is beta-testing for King County makes it possible to ask these questions with the expectation of useful answers — a relatively new phenomenon because of historic limitations in tracking fish.
Researchers have been injecting adult fish with electronic tags for years. These tags, about the size and shape of a Good & Plenty candy, are extremely low maintenance. Unlike Tile trackers that you would use to find your keys, these trackers use the radio frequency identification, or RFID, technology you would find in a credit card. They don’t need batteries and can sit in a salmon’s body for its entire life without needing updates.
Scientists track tagged fish by installing sensors alongside rivers: When fish pass within a few feet of them, the sensors detect the tags and read their data. That’s a huge improvement over traditional methods of tracking. In the past, some scientists injected fish with tags that you had to extract and read manually. Others colored fish with ultraviolet paint. For both techniques, researchers had to re-collect fish after releasing them, says “which is absolutely impossible,” Gregersen says.
To inject a tag into a fish, ecologists first place them into anesthesia baths like the one Gregersen has set up at the Icy Creek hatchery. Ecologists then load up what looks like a child-size glue gun with a tag and carefully inject it into asalmon toward its tail fins. It’s a delicate process.
“The more they eat, the squishier they get — to the point where you start pushing and pushing and then if it just pops, obviously, the needle could poke something you don't want it to. So this spring we actually had to set our hatchery fish aside and not feed them for several days,” Gregersen says, fish in hand.
The problem with earlier versions of RFID-tagging technology was that the fish in this study — juveniles — are small, about 2 inches when they start swimming downstream. Two could easily fit on top of your cellphone. Neither has much internal real estate for tracking devices. So when King County found out about newer rice-sized tags, it jumped on them.
The tags are encapsulated in glass, making them inert, and the process leaves behind a small incision that heals in a few days. The fish wake up in about a minute. The mortality rate is one in a 1,000 fish, and they haven’t documented any fish losing their tags so far.
Gregersen started tagging in March, about a month after juveniles show up in river systems, and has so far equipped at least 1,000 wild-caught juvenile fish and 3,000 hatchery fish with the technology.
The tags pair with a 4,000-pound floating sensor barge, designed by West Fork Environmental and attached with strong cables to the Southcenter pedestrian bridge. Eventually, fish tagged today at Icy Creek will pass it.
This barge has been tested a few times in Eastern Washington, but never before in the Puget Sound area.
Travis Olsen, a fisheries biologist with the Confederated Tribes of the Umatilla Indian Reservation, says using the barge technology beginning in 2019 made a big impact in the tribes’ ability to track fish, including Middle Columbia summer steelhead and spring chinook. It allowed them to track in deeper water toward the mouth of the Walla Walla River, with less repair concerns than they’d have with things like anchored sensors.
Altogether, the King County project clocks in at $300,000.
Preliminary fish-tracking results
So far, Gregersen says, preliminary data have been promising, revealing things about fish activity that we didn’t know before, including that detected fish are staying in the Lower Green anywhere from two to 63 days, with smaller fish sticking around longest.
This was huge, Gregersen says: “Up until now, we didn’t even know if fish used this highly modified habitat.”
Research suggests smaller fish need off-channel habitat, like small tributaries, which can be refuges during high river flows. Fewer of these places exist in urban rivers. Built-up shorelines prevent erosion, but reduce nooks and crannies where juveniles can rest and forage, and barriers make it hard to get in and out of them from calmer tributaries.
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