Qualitative observations of Dungeness crabs, <i>Cancer magister</i>, in and around traps: evidence of resource guarding and clustering

Decapod crustaceans are well known for agonistic interactions where they commonly fight over resources. Accurate descriptions of crab behaviour are essential to the development of quantitative behavioural studies involving the Dungeness crab fishery. An underwater video system mounted over a commercial crab trap <i>in situ</i> was used to qualitatively describe several of the most common behaviours utilized by <i>Cancer magister</i> in and around traps, including the documentation of previously undescribed behaviours in this species. Crabs commonly guarded trap doors without entering the trap and prevented other inspecting crabs from entering the trap. Agonistic interactions in traps ceased when crabs ‘clustered’ together, creating a group of non-interacting, fairly motionless crabs sitting on or near each other. These observations indicate that crab behaviour merits further attention in future studies of gear saturation and the catchability of Dungeness crabs.