Reproductive Ecology of the Japanese Mitten Crab Eriocheir japonicus (DE HAAN) in Its Marine Phase

Abstract

The reproductive ecology of the Japanese mitten crab Eriocheir japonicus in the sea was investigated by sampling and rearing crabs from Tsuyazaki, Fukuoka Prefecture, Japan, in 1990 -1991. Crabs, including ovigerous females, were collected in the field from early September to early July. Carapace width distributions for field-collected dead and live specimens did not differ. Crabs of both sexes reared in the laboratory died without moulting by August. These deaths were concentrated in two periods - November to December and again in April to June; this agreed with the periods of collection of dead crabs in the sea. Therefore, in the sea most crabs seem to die after reproduction without further moulting and growth. Female crabs oviposited and hatched eggs up to a maximum of three times. The volume of the egg mass tended to decrease in later ovipositions. There seemed to be two groups that differed in the timing of oviposition and death. Crabs that migrated to the sea in September and October tended to be larger than those migrating later.