Abstract
At Rausu Town, northeast of Hokkaido, collection of a high-priced edible sea urchin Strongylocentrotus intermedius is prohibited for resource conservation during the spawning season from July to September. Furthermore, the removed maturing gonads are not good for commercial use because they easily ‘melt’ (collapsed). However, the urchin gonad is a potential natural food product particularly in the summer season in which most abundant tourists visit the town in a year. During summers in 2003 and 2004, maturation control was tried by culturing the collectedsea urchins in land-based tank (0.5 ton in volume) using deep seawater (DSW) colder than surface seawater (SSW). In June 2003, half of the sea urchins (>50 mm in diameter, N = 240 in June 2003) were fed with kelp, while the others were keptunfed. Gonads of fed, unfed and wild sea urchins were biweekly evaluated using standard criteria comprised of 5 stages (I to V). The deep seawater was pumped from a depth of 218 m, 1.4 km off Chienbetsu Fishing Port and the water temperature was kept between 2 and 4°C by circulating and chilling. In 2003 (2004), the most valuable gonad stage III accounted for 47 (70) % at the commencement of stock-cultured on June 25th (May 11 th) and lowered below 10% on August 20th (September 14th) in fed andon August 20th (August 17th) in unfed sea urchins. On July 23rd (August 17th), when gonads lowered below 10% in wild urchins, the ratio ofstage III accounted for 27 (35) % in fed and 40 (10) % in unfed sea urchins. In asensory test conducted in 2004, gonads in stage III of both fed andunfed sea urchins marked fine scores (higher than middle among five ranks) on taste and outlook till July 6th (stock-cultured for 56days).
