If a lobster gets in the trap first does it chase crabs out?
I did my master's thesis on behavioral interactions between lobsters and crabs (Jonah and sand crabs, Cancer borealis and Cancer irroratus) and how they affect trapping of these species. What I found was that if a lobster got into a trap first, crabs would not enter the 'parlor' or holding section. This was because if a crab started up the entry to the parlor, the lobster made aggressive displays which made the crab back down. Crabs did not keep other crabs out, nor lobsters, so if a crab got in first, lobsters would still come in. In general, these two species of crabs are less aggressive than lobsters.