Use of oyster shell to create habitat for juvenile Dungeness crab in Washington coastal estuaries: Status and prospects

The deployment of oyster shell in estuarine intertidal areas to create habi tat for juvenile Dungeness crab (Cancer magister) is now used routinely as mitigation for "unavoidable losses" of crab during dredging operations in G rays Harbor and Willapa Bay along the southwest coast of Washington State. Feasibility studies were conducted in 1986 to 1987 for a U.S. Army Corps of Engineers project to widen and deepen the navigation channel in Grays Harb or. Since that lime, several studies have elucidated the ecology of crab an d other organisms that recruit to the created shell reefs. Studies have als o refined the procedures used to calculate crab losses caused by dredging a nd crab production in the shell habitat. The shell does serve as crab habit at: however, initial assumptions about the longevity of the shell have prov ed to be overly optimistic, because the shell can sink or be covered with s ilt before the end of the first summer after deployment. In addition, compe tition with the shore crab, Hemigrapsus oregonensis, has displaced juvenile Dungeness crab. We summarize results of these studies and present initial results from an ongoing mitigation effort that seeks to produce a more pers istent living oyster reef in Willapa Bay.