Scientists paint fish to ease tracking

Friday, June 7, 2002

LOGAN, Utah -- With a red slash at the throat, the cutthroat trout destined for Strawberry Reservoir wouldn't seem to need much more color. But then, would a dab of chartreuse really hurt?

Thousands of trout at the Fisheries Experiment Station are getting that extra dash of color, via spray paint, in a program that allows biologists to keep track of their numbers and development. Once in the lake, the 6-inch trout will swim among older generations of fish painted red or yellow.

While Val John Halford, a volunteer, stands thigh-deep in a tank, a net-load of yearling trout flop in a perforated box. The water drains out, and the fish flop harder. Alan Ward of the Utah Division of Wildlife and Fisheries sprays them with an air-powered paint gun.

They'll paint 39,000 in about three hours. Around half a million are marked each spring.

Fine, colored sand penetrates under the trout's tiny scales. Months or years from now, when biologists conduct gill-net surveys, the sand will show up under ultraviolet light. Color and size tells the biologists where the fish came from. The paint is harmless and invisible to the naked eye.

Some of these 6-inchers won't last long in the big lake, falling victim to larger trout. Others will fall for fishermen's spoons or flies. In four or five years, the fish Ward and Halford paint today will be gone, Ward said.

Some don't even make it to the lake. While most of the trout swim away after Halford dumps them back into the tank -- each sports garish scars of green graffiti -- a few go belly-up.

"There's always a potential for problems whenever you handle fish. Overall, it's pretty harmless," Ward said.

But it's worth the risk. Keeping the fish population healthy in the 17,000-acre reservoir, one of Utah's top trout lakes, requires a delicate balance.

Things got out of hand in the late 1980s. Rough fish, like the Utah chub, were crowding out the trout. State wildlife officials annihilated the whole lake with chemicals in 1990 and started over -- this time with spray-painted fish.

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