1Fisheries Technology Department, Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center, Miyazu, Kyoto 626-0052, 2Japan Sea National Fisheries Research Institute, Fisheries Research Agency, Chuou, Niigata 951-8121, Japan
This paper describes the estimation of catch in number of soft-shelled males Chionoecetes opilio caught by commercial Danish seiners and their survival ratio just after release at sea during the snow crab fishing season (Nov.-Mar.). Soft-shelled males are sexually non-functional with low commercial value. Soft-shelled males caught by Danish seine were put in experimental traps, and soaked in the fishing ground for about six hours, then retrieved to the research vessel for observation of their survival/mortality. Mean total catch in number of soft-shelled males was estimated at 168,400 individuals in the waters off Kyoto Prefecture based on the fishermen's log-books received in 2006-2008. The estimated number of soft-shelled males is approximately 1.7 times higher than that of hard-shelled males. The survival ratio of soft-shelled males released was estimated at 14.8-95.9% for small size (90-109 mm CW), 5.0-89.8% for medium size (110-129 mm CW), and 0-62.5% for large size (≥130 mm CW). If landings of soft-shelled males were prohibited, the mean survival rate during the soft-shelled male fishing season (Jan.-Mar.) would be as high as 83.6%. This suggests that the protection of soft-shelled males leads to an increased abundance of hard-shelled males resulting in higher economic benefit.