CAMP SHERMAN, Ore. — Sitting on the banks of the Metolius River with a black garbage bag covering her head and hands, biologist Megan Hill shone an ultraviolet light on a tiny chinook salmon.
Swimming in a plastic bucket, the fry look like any other — light brown with dark spots and a pale belly.
But look at some under an ultraviolet light, and their bones glow a neon green.
Two thin, curved lines of green pop out on either side of the fish’s head, illuminating the jaw bone. Fainter splotches of green appear behind the lines.
The green is the result of an experimental dye that biologists used to mark and identify the fish. About 70,000 of the fluorescent-dyed fish are now swimming in stretches of the Metolius River; biologists soaked them in the dye, rinsed them off and then released them along with thousands of other unmarked chinook in February.
While the green bones aren’t visible to the naked eye of either humans or other fish, researchers hope the marking technique, using calcein, will be able to help them distinguish the released fish from the native species.
Staff with Portland General Electric, the Confederated Tribes of Warm Springs and the Oregon Department of Fish and Wildlife are releasing thousands of steelhead and chinook salmon fry into tributaries of the Deschutes and Crooked rivers to try to jump-start runs of the oceangoing fish.
But they need a way to tell the hatchery-born steelhead from the wild-born redband trout, since the two are the same species and look identical as fry, said Megan Hill, a fish biologist with PGE.
And the normal ways of marking fish, such as clipping fins, would be too difficult for such large numbers of fish that are only about 1 1/2 inches long.
“Handling each and every fish would be a huge amount of time,” Hill said. “There just aren’t a lot of options for marking fish that small.”
While calcein isn’t yet approved by the Food and Drug Administration, tests like this one are part of the process to get that OK, said Dave Erdahl, branch chief of the U.S. Fish and Wildlife’s aquatic animal drug approval partnership in Bozeman, Mont.
But even for these trials, the Fish and Wildlife Service still had to show that the chemical doesn’t pose a hazard to the fish, the environment or people who might eat the fish, he said.
Only fish that weigh less than 2 grams are dyed, Erdahl said, and by the time they have grown enough for people to eat them, the amount of calcein still in the fish is “infinitesimal.”
Plus, the chemical degrades over time as the fish are exposed to sunlight, Hill said. The fish wouldn’t be caught and eaten for several years, and studies have shown that it’s not present any more in the meat or kidneys of adult fish, although traces could still be in the bones.
The fish she has treated seem to be doing fine, she said.
“We haven’t seen any effect on survival and growth, and no one really has,” she said.
To see how well the dye was working, Hill and Cory Quesada, another fish biologist with PGE, waded along the banks of the Metolius River recently.
Quesada held a device that sent a small electric current through the water, drawing the fish, while Hill followed with an aquarium net to scoop the salmon up and drop them in a bucket.
To determine whether they were marked or not, Hill slipped a black garbage bag over her head to create a makeshift darkroom. Wearing amber-filtered glasses, she picked up the fish one by one, and shone a hand-held ultraviolet light on them, looking for green streaks along the jaw bones.
“Right when we first marked them, it was bright green, it glowed,” she said. “Now it’s getting tougher to tell.”
The dyed chinook are, in part, a test to see how well the dye will work with the steelhead, she said, which will be marked and released in mid- and late May.
Both the chinook and the steelhead are part of a massive effort by PGE and the tribes to bring oceangoing salmonids to the Upper Deschutes again, after the construction of the Pelton Round Butte dam complex blocked their route about 50 years ago.
The fish reintroduction is one of the requirements in the dam relicensing agreement. Another requirement, Hill said, is to keep track of what happens to the resident redband trout when the steelhead and chinook come back, to make sure the reintroduced steelhead don’t hog the redband’s habitat.
And in order to do that, the biologists need to be able to tell the different species apart, and they needed a way to mark the hundreds of thousands of fish they would release.
The dye would make monitoring more effective and help biologists determine how successful the reintroductions are, said Brett Hodgson, a fish biologist with the Oregon Department of Fish and Wildlife.
“If, in fact, this dye works, it would be ideal because that would enable us to differentiate between steelhead fry and resident redband trout fry,” he said.
One concern that both he and Hill mentioned, however, is that the dye will degrade over time, and so it won’t be visible to the people out monitoring the population.
This year is a test year for the dye, Hill said, and if it works it could be a multiyear program; if it doesn’t, the biologists will look for something new.
“We’re kind of treading into new waters here, so to speak,” Hodgson said.
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