Relationship between water temperature and catch of the kelp Saccharina japonica var. ochotensis in northern Hokkaido, Japan

Abstract

The kelp Saccharina japonica var. ochotensis is the most important algal resource in northern Hokkaido, Japan. The species is biennial, and fishing of the kelp is limited solely to second year sporophytes. Annual change of monthly mean surface water temperature and catch of the kelp S. japonica. var. ochotensis in northern Hokkaido, Japan, from 1980 to 2016 were compiled based on data from public organizations. Over this period, increasing water temperatures in each month contrasted with a decreasing catch of kelp. Statistical analysis using Pearson Correlation Analysis Method was conducted between mean monthly water temperature and catch of S. japonica var. ochotensis in each year. A significant correlation was found between water temperature from September to December one year prior to the fishing year and the catch of the kelp. In general, fewer individuals of the kelp transit from first year sporophyte to second year sporophyte during from October to November, and this decreased rate of transition impacts the catch. The present study suggests that lower temperatures during September to December would lead to a higher transition rate from first year sporophytes to second year sporophytes, which in turn would lead to a higher catch of kelp the following year.