Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8884
Title: A preliminary survey of benthic invertebrates in the vicinity of the Coos Bay, Oregon, navigation channel
Author/Editor: David R. Miller, Robert L. Emmett, Susan A. Hinton
Publication Year: 1990
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon

Potential biological impacts of deepening the Coos Bay, Oregon navigation channel from river mile (RM) 0 to 15 were discussed at an interagency meeting in March 1989.  A cooperative agreement was reached between the U.S. Army Corps of Engineers and the National Marine Fisheries Service to collect sediment samples at selected intervals over the length of the project and to determine the distribution and abundance of benthic invertebrates. 

Our preliminary survey of the Coos Bay navigation channel indicated the presence of a diverse and, in some areas, dense benthic infauna.  However, based on this limited sampling, benthic invertebrate densities appear to be generally lower than those of the Umpqua River estuary, where invertebrate densities ranged from less than 200 to over 50,000/m2 and the Columbia River estuary, where densities ranged from less than 1,000 to over 60,000/m2.  Nonetheless, a channel deepening project of this magnitude has the potential to markedly alter ecological relationships by changing the complex pattern of freshwater inflow, tidal circulation, estuarine flushing, and freshwater and saltwater mixing.  More direct biological impacts are also likely as side-channel sloughing increases the channel width.  Additional survey work will be required to evaluate benthic species composition and density at stations adjacent to the existing channel and to obtain critical data on natural seasonal variation in infaunal community structure.