A comparison of survival rates until recruitment for hatchery-released Japanese Spanish mackerel Scomberomorus niphonius with different sizes at release

¹Tamano Station, National Center for Stock Enhancement, Fisheries Research Agency, Tamano, Okayama 706- 0002, ²Yashima Station, National Center for Stock Enhancement, Fisheries Research Agency, Takamatsu, Kagawa 761- 0111, ³Kagawa Prefectural Fisheries Experimental Station, Takamatsu, Kagawa 761- 0111, ⁴Obama Station, National Center for Stock Enhancement, Fisheries Research Agency, Obama, Fukui 917- 0117, ⁵Faculty of Marine Science, Tokyo University of Marine Science and Technology, Minato, Tokyo 108- 8477, Japan

Efficiency of recruitment of hatchery-reared juvenile Japanese Spanish mackerel Scomberomorus niphonius was evaluated based on estimates of the survival rate after release. Experiments of juvenile release were carried out in 2002 and 2003 to compare the survival rates of 40 mm juveniles released directly from the production tank with those releases after rearing in net cages in the sea up to 100 mm in total length. The ratio of survival rates of the 2 groups was estimated at 4.10 for 2002 and 3.13 for 2003. Recruitment to the wild population was more efficient in the 100 mm juvenile release than in the 40 mm juvenile release in terms of the production costs and survival after release.

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