【Reading】しゅびょうほうりゅう

【English Name】Seedling Release / Stock Enhancement

Shubyo-horyu (seedling release) refers to a method of sending out into the sea or rivers young fish and young shellfish raised at facilities. It is positioned as a core process within sea farming (saibai-gyogyo), called the fishery that creates and raises.

This method first emerged in the 1960s in the Seto Inland Sea. In 1962, the state established bases on Yashima in Kagawa Prefecture and Hakata Island in Ehime Prefecture. The following year, 1963, the Seto Inland Sea Farming Fisheries Association was launched. In time, national sea-farming fishery centers expanded to 16 locations nationwide, and the number of prefecture-run facilities reached 64.

How to set the body length at the time of release is cited as a major practical challenge. Returning fish to the sea after growing them sufficiently raises the survival rate in the wild, but the rearing cost swells. Conversely, releasing them at a small stage allows greater numbers, but the probability of establishment drops. Within this trade-off, finding the optimal solution that judges cost-effectiveness is essential. As a device to protect young fish from predators, a method of sending them directly near the seabed through a wide-mouthed hose is adopted in various places.

The targets of release are wide-ranging, extending from fish in general such as red sea bream, flounder, and tiger pufferfish (torafugu), to crustaceans and echinoderms such as kuruma-ebi, abalone, sea urchin, and sea cucumber. Similar efforts are advancing for sweetfish (ayu) and salmon species in various rivers as well, but there are persistent voices concerned about genetic crossbreeding with wild populations originally inhabiting those waters and about adverse effects on the genetic structure of native populations.