Department of Integrative Biology

Cancer oregonensis is a predator of sub-market size oysters (Crassostrea gigas). Crabs enter oyster trays as megalops larvae between May and October, and attain a carapace width (CW) of 30 nun within a year. Despite its small size, Cancer oregonensis has powerful chelae; molar teeth and sharp tips are well adapted for crushing and puncturing oysters. In laboratory experiments the largest C. oregonensis (43 mm CW) was able to open market size oysters larger than 60 mm in length, while even a 20 nun wide crab consumed oysters 30 mm in length. Medium size crabs (20-35 mm CW) consumed an average of one young oyster (20-40 mm in length) per day. A field experiment was set up in which 15 trays, each containing 315 +/- 23 seed oysters, received 5, 2 or 0 newly settled C. oregonensis. Ten months later the average survival of oysters in the two crab treatments was 63% and 69% versus 90% for the control treatment. We recommend that crabs be manually removed during sorting operations.