Seasonal changes in the vertical distribution of North Pacific giant octopus Enteroctopus dofleini in a box-fishery off northern Hokkaido in the Sea of Japan

The seasonal vertical distribution and biological characteristics of North Pacific giant octopus Enteroctopus dofleini were investigated using box-fisheries data in the Sea of Japan off the coast of northern Hokkaido between 2006 and 2011. The results showed that the depth distribution of E. dofleini was >50 m from August to September, <40 m from October to December, 30-60 m from January to February, <30 m from April to May and 20-50 m from June to July. Most individuals were immature with body weights ranging from 2.5 to 10.0 kg (mean 5.7 kg). The most abundant food items included Urechis unicinctus, various fish, crabs, and octopus. The results showed that immature octopuses in this fishery appear to undertake two seasonal migrations per year.