The behavioural interactions between the American lobster (Homarus americanus) and the invasive green crab (Carcinus maenas)

The American lobster (Homarus americanus) is the most commercially important decapod species in Newfoundland. Since the 1990s, fishery landings in Placentia Bay, Newfoundland have been steadily decreasing. The invasive green crab (Carcinus maenas) was first recorded in North Harbour (Placentia Bay) most likely in 2002, and shortly after this, lobster landings decreased by 34% compared to previous years. Analyses of the behavioural interactions between the two species around a food source and a baited trap were used to better understand the potential impacts of green crabs on lobsters in the natural environment. The presence of green crabs (1-25 animals) had no significant effect on the ability of lobsters to acquire food, but they did negatively impact lobster food consumption when present in high numbers (150 crabs). Agonistic interactions between the two species increased with green crab density. Green crabs also significantly affected lobster behaviour around a baited trap; when green crabs were present and could freely move around the trap, a lobster approached, attempted to enter and successfully entered less frequently compared to trials when no crabs were present. Analyses of predator-prey interactions between adult lobsters and green crabs were also used to determine if lobsters from Newfoundland would recognise green crabs as a potential prey item. Lobsters originating from Nova Scotia and Newfoundland actively consumed green crabs of all sizes and the size of the green crab determined the likelihood of being damaged and consumed by a lobster. The longer a green crab remained in the presence of a lobster, the more likely it would be captured and eaten. This research provides information on the potential impact of green crab on the lobster fishery in Newfoundland and Labrador and may be used by stakeholders in the management this fishery