Cannibalism in the Japanese mitten crab, Eriocheir japonica

Cannibalism is ubiquitous in crustaceans but relatively little is known about the degree of cannibalism in the Japanese mitten crab, Eriocheir japonica (De Haan, 1835). In this study, we examined the possibility of cannibalism in intermolt Japanese mitten crab in relation to predator–prey size difference, predator sex, prey density, and presence of alternative food and shelter under laboratory conditions. Predator crabs were starved for 48 h and then exposed to smaller conspecifics as prey for 24 h, after which the number of dead/injured prey was recorded. Our results indicated that E. japonica cannibalizes conspecifics when the relative size difference between cannibal and victim becomes large. Males were more cannibalistic than females and predated on conspecifics following a type II functional response. The presence of alternative food and shelter effectively mitigated cannibalism. The extent of cannibalism in the field remains unknown but we hypothesize that the segregated distribution pattern of E. japonica along river courses may be an evolutionary adaptation to reduce intraspecific predation.