Friday, May 24, 2013

Scientists study Silver Creek insects

Will proposed dredging improve trout habitat?

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By GREG MOORE
Express Staff Writer

Scientists installed insect-collection devices called “samplers” in Silver Creek earlier this week. Courtesy photo

     Devices to measure invertebrate populations were installed in Silver Creek this week in anticipation of a proposed dredging project at Kilpatrick Pond.

     The project is planned by The Nature Conservancy, which manages land above the pond, and Picabo Livestock Co., which owns land along the pond and immediately downstream. The intent of the project is to create deeper channels through the pond and reduce the water temperature downstream to improve trout habitat.

     Dayna Gross, Silver Creek watershed manager for The Nature Conservancy, said the five-year study will gauge conditions before and after the project.

     “We’ll measure to find out how fast it’s recolonized,” Gross said.

     The study is being conducted by Terry Maret, a biologist with the U.S. Geological Survey’s Idaho Water Science Center. He said the USGS has been collecting data on invertebrates at the site since 1997, along with the Idaho Department of Fish and Game, which has been monitoring fish populations, and The Nature Conservancy, which has been taking temperature and dissolved-oxygen measurements.

     This week, Maret installed devices called Hester Dendy samplers, an “artificial substrate” consisting of 14 Masonite plates attached to vertical tubes driven into the streambed. The plates, which have a variety of spaces between them, provide habitat for different aquatic invertebrates.

     “It creates spaces for insects to crawl into and live,” Maret said.

     One sampler was installed above Kilpatrick Pond, one in the pond and one below it.

     Maret said invertebrates that he expects to collect include caddisflies, mayflies and stoneflies, as well as snails and leeches. All are trout food.

     He said previous sampling has shown fewer stoneflies—a cold-water species—below the pond than above it.

     Maret said he will collect the creatures that have moved into the samplers in six weeks and reinstall the samplers in mid-July. He will do the same in late summer and in the fall, since different species emerge at different times of the year.

     “They all have different lifecycles,” he said.

     He said he will repeat the process in two years, and a report on the findings will be released in 2017.

     He said that in addition to helping to gauge the success of the proposed dredging project, the study will provide concrete data to anyone contemplating a similar project elsewhere.

     Gross said she’s “pretty darn confident” that the study will confirm The Nature Conservancy’s claim that the project will improve trout habitat.

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Greg Moore: gmoore@mtexpress.com

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