Behaviour and growth of captive spiny lobsters (Panulirus argus) under the risk of predation

The behaviour and growth of captive spiny lobsters (Panulirus argus) under and not under the risk of predation was investigated in four 9-m² sea enclosures: two 'predator enclosures' (P1 and P2) into which one predator, the triggerfish Balistes vetula, was introduced; and two 'nonpredator enclosures' (NP1 and NP2). Each enclosure contained a 1-m² artificial shelter, and lobsters were provided with food ad libitum for 45 days, measured then left for a further 30 days with a reduced food supply. Inter- and intraspecific interactions and shelter use were recorded by means of underwater observations during day and night. Daytime shelter use by lobsters and fish was highest at noon and in the early morning. Activity of lobsters outside the shelters peaked around midnight in all four enclosures. Lobsters in P2 showed more activity and less shelter use than did those in all other enclosures. More predator-prey interactions were recorded in P1 than in P2, whereas intraspecific interactions were more prevalent in P2 than in the other three enclosures combined. Growth of lobsters was significantly higher only in NP1. The difference in lobster behaviour and survival between the two predator enclosures may be associated with the initial timing of shelter occupancy by the predators.