Relationship between Year-to-year Fluctuations in Recruitment of Juvenile Sea Urchins Strongylocentrotus nudus and Seawater Temperature in Southwestern Hokkaido

Year-to-year fluctuations in the recruitment of the juvenile sea urchin Strongylocentrotus nudus were monitored between 1980 and 1995 off the coasts of Okushiri Island and Shimamaki on the Sea of Japan coast, southwestern Hokkaido. High recruitment levels (14.1 ind./m²) of juveniles in 1984 and a continuous recruitment after 1990 were observed at the survey areas. The relationship between juvenile densities and average water temperature in September of the previous year was statistically significant. We suggest that high water temperature in September contributes to shortening of the larval period. The dominant 1983 year-class population contributed to an increase in commercial catch at the survey areas, and this was also found in the sub-prefectures of Shiribeshi and Hiyama.