DISTRIBUTION, ABUNDANCE, AND FOOD HABITS OF THE DUNGENESS CRAB, CANCER MAGISTER, IN GRAYS HARBOR, WASHINGTON

The Dungeness crab, Cancer magister, which supports a major Pacific coast fishery, often occurs in large numbers in coastal estuaries, but the importance of these habitats is unknown. In Grays Harbor, Washington, a major proposed dredging project threatens to destroy several million crabs.;Growth of three year classes was followed separately. First instar postlarvae which metamorphosed in May 1980 were 7.2 mm carapace width and .023 g dry weight (d.wt.). Crabs averaged 45 mm and 4.2 g d.wt. after one year, and 85 mm and 25.5 g d.wt. after two years in the harbor. Growth was rapid from May to October, but slow during winter.;First year crabs preyed greatly on small bivalves and crustaceans. Larger crabs switched to larger invertebrates (Crangon shrimp) and later to juvenile fish. Night-time foraging movements onto intertidal mudflats were associated with high Crangon abundance and predation.;The results of this research show that Grays Harbor is an important habitat for juvenile crabs. Changes in food preferences and density with age may allow partitioning of food and space resources among the various age classes. Population estimates will allow better estimation of the relative mortality caused by dredging and habitat changes.;The crab population of Grays Harbor was surveyed from May 1980, to July 1981. Crabs were collected by trawl at nine stations, and by ring net at three stations, at monthly or bimonthly intervals. Early postlarval crabs were most abundant on or near mudflats with eelgrass beds. One year old crabs were widespread throughout the harbor, and older crabs were most abundant in the central outer harbor. Crab densities fluctuated seasonally; population size was estimated to range from three million (winter) to thirty million (summer) due to a great influx of megalops larvae and first instar crabs in April-June. Using known and estimated mortality rates, it was estimated that young-of-the-year crabs in Grays Harbor could provide 50-80% of the crabs caught by the offshore fishery 3.5 years later.