Effects of habitat complexity on the aggressive behaviour of the American lobster (Homarus americanus) in captivity

The American lobster, Homarus americanus, is one of the most economically valuable crustacean decapods worldwide, being mostly exploited to foster the live animal industry. Lobsters are typically held in storage facilities where individuals may suffer due to the repeated combats among each other. Loss of chelae and other damages may also reduce their market value. Here, we investigate the potential use of a complex habitat to reduce fighting in a group of lobsters. Pieces of concrete bricks positioned within the experimental tanks were used to increase the complexity of the habitat. The behaviour of groups of four similarly sized lobsters in these tanks was recorded for an hour for a total of seven trials for three consecutive days and was compared with the behaviour of similar groups maintained in simple habitats. The results showed, first, that habitat complexity reduces the agonistic intensity of interactions and the time spent fighting and, second, that this reduction remains constant with time. It is finally suggested that a complex environment may “distract” lobsters and interfere with the transmission of the stimuli used to detect conspecifics. Our results, although provisional, provide valuable suggestions for lobster storage. Habitat enrichment, combined with shelters, might serve as a cheap and easy method to reduce lobsters’ aggression in captivity, being less invasive than chelae immobilization, on one hand, and more respectful of animal welfare, on the other.