Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8841
Title: Benthic invertebrates and demersal fishes at an interim dredge-disposal site off Willapa Bay, Washington
Author/Editor: David R. Miller, Robert L. Emmett, Robert J. McConnell
Publication Year: 1988
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Environmental Protection Agency. Seattle, Washington

In July 1985, the National Marine Fisheries Service (NMFS) entered into a cooperative agreement with the Environmental Protection Agency (EPA) and the Seattle District Corp of Engineers to conduct an ecological survey at a proposed interim dredge disposal site off Wiliapa Bay, Washington, between 30 July and 1 August 1985.  Previous studies at the proposed site (10-15 fathoms) by Simons (1984) and Shapiro and Associates, Inc. (1985) indicated high benthic invertebrate densities similar to those found off Tillamook Bay, Oregon, (>70,000 organisms/m2) at 10-20 fathoms by Emmett et al. (1987).

As a result, EPA requested additional benthic invertebrate sampling prior to final site designation.  However, the Willlapa Bay interim disposal site was subsequently moved to deeper water (10-24 fathoms) because of the intensive commercial crab fishery at the original site, and it was at this new site that our sampling took place. 

Benthic invertebrate communities are commonly monitored during environmental assessment surveys.  Benthic invertebrates are useful indicators of environmental conditions because  1) they are in contact with bottom sediments (dredge spoils),  2) being relatively immobile, they may be either transported or burled by dredge spoils, and  3) they provide a critical link In the food chain (Morton 1977). 

Bottom trawl surveys and sampling fishes and crabs at dredge sites can be important in determining what species use an area for migration, spawning, rearing, or feeding.  However, dredging effects on fishes and crabs are difficult to quantify because of these animals' mobility, contagious distribution, and ability to avoid disturbed habitats.

Combined benthic invertebrate, fish, and crab surveys are especially useful in identifying both the diversity and structure of the benthic community and in distinguishing possible food-web linkages between infauna and vagile epifauna (fishes and crabs).