Gregarious?
There have been no behavioural studies on adult lobsters in deep water. Because gregarious behaviour in juveniles increases with size, it is likely that adults also display these behaviours, grouping up in dens rather than being solitary. Laboratory experiments on animals 77 – 85 mm CL (around the size of sexual maturity) have indicated that western rock lobsters prefer to be housed in groups, with greater movement and food consumption rates observed in animals in groups of three and four, compared with lobsters housed alone or in pairs (Waddington et al. 2005).
Aggressive?
However, on the other hand, there is evidence that larger lobsters may display increased antagonistic behaviours. In underwater observations of juveniles, Cobb (1981) noted that if a den was too crowded:
“there would be some movement after the new lobster had entered, and after a brief aggressive encounter, one of the lobsters would leave the den and walk directly to another.”
Similarly, aggressive interactions between lobsters (76 – 85 mm) have been observed around pots in a laboratory setting (Konzewitsch 2009). Furthermore, aggressive behaviours may increase with increasing size. Studies on catch rates have revealed dominance behaviours in larger animals, with large lobsters excluding or deterring smaller animals from pots (Chittleborough 1974, Tuffley et al. 2021). If aggressive behaviours are more common among larger animals, it is possible that adults in deep water habitats are less gregarious than juveniles in the shallows.