Benthic Patterns and Processes

Dungeness Crabs - Movement patterns and Feeding Ecology

Focus: Dungeness crab is an ecologically and economically important species that can be found from the intertidal to at ~180 m in sand, mud, and eelgrass beds. It is an ODFW strategy species and the retained catch averages around 17 million pounds in Oregon annually.

Issue: Based on our many years of benthic surveys and on-going calorimetry work we find a mis-match in the amount of benthic biomass and the energetic requirements of the biomass of Dungeness crab landed each year.

Project: Crab Feeding Ecology

Hypothesis:We hypothesized that the influx of calories to the seafloor that occurs seasonally in the form of bait from the crab fishery - either as hanging bait in the pots or dumped overboard as spent bait - is a significant portion of Dungeness crab diets and may be a reason Dungeness are able to maintain large populations despite little other benthic biomass and intense fishing pressure.

Approach: We characterized the feeding ecology of Dungeness crab in three regions off Oregon to investigate the relative contributions of bait versus conspecifics (cannibalism) versus other benthic species in their diets by:

• examining gut contents of crabs

• conducting stable isotope analysis (bulk δ¹³C and δ¹⁵N) of crab, benthic prey, and bait

• surveying fishermen & bait suppliers for estimates of type, quantity, and mode of bait use

• determining the caloric density of the major bait types to estimate annual seafloor subsidy