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Pacific Northwest National Laboratory researchers and U.S. Army Corps of Engineers cadets count crabs that have been entrained during dredging on the Columbia River for an assessment the Laboratory is doing for the Portland District of the U.S. Army Corps of Engineers.

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Document Title: Crab Entrainment Study
Category: Wildlife and Environmental Studies
Media Type: Photos
Date of Image/Photo: Summer 2002
Background: The Columbia River, which serves as a waterway for export commerce from the West and Midwest, must be dredged yearly to keep the river bottom deep enough for safe navigation. During dredging, Dungeness crab are taken up with the dredged materials. The Portland, Oregon, District of the U.S. Army Corps of Engineers, which is sponsoring the assessment, is concerned about the effects of dredging on the crab population. Working for the Corps, PNNL scientists are assessing how the dredging and disposal of dredged materials will affect the crab population. "We're providing scientific information on crab that can be used to make decisions in a way that minimizes the impact," said Walt Pearson, director of the PNNL project. PNNL researchers are looking at crab entrainment, or how many crab are trapped by dredges. During the dredging process, sediment and crab from the river bottom are taken up through pipes and passed into a hopper aboard the dredge. When the hopper is full, its contents are released at a dumpsite. Scientists are trying to find out how many crab are being trapped as the dredge fills up and what happens to those crab that get buried by sediment when the hopper is emptied.
URL of this page: http://picturethis.pnl.gov/picturet.nsf/by+id/AMER-5EGLW2

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