Effects of the invasive green crab (Carcinus maenas) on American lobster (Homarus americanus): Food acquisition and trapping behaviour

Abstract

The American lobster (Homarus americanus) is the most commercially important crustacean species in Eastern Canada. Fishery landings in Placentia Bay, Newfoundland have decreased steadily following the cod moratorium in 1992, with another noticeable drop in 2002 when the first invasion of the European green crab (Carcinus maenas) was likely to have happened. The effect of green crabs on the food consumption and catchability of lobsters was quantified in relation to crab density (n = 0, 1, 5, 25) and water temperature (4 °C, 12 °C). Food acquisition and behavioural responses of lobsters were unaffected by the water temperature or crab densities of 1 to 25 animals. However, when a lobster was pitted against 150 crabs they were unable to obtain any food and the crabs consumed all the food within 8 min. In contrast to lobsters, the green crabs consumed more food at the higher temperature because they were more active. As crab density increased the number of agonistic interactions and retreat behaviours increased at both temperatures, and crabs were more likely to retreat from a lobster than vice versa. The effects of green crabs on the catchability of lobsters around a baited trap was also investigated when crabs were freely mobile outside the trap or contained within the trap. Lobsters were more likely to approach and enter the trap at 12 °C than at 4 °C, however, they were also more likely to escape. Lobsters were less likely to approach or enter a trap if they interacted with crabs outside the trap. The present results suggest that interactions between green crabs and adult lobsters may influence lobster catch rates in Newfoundland.