Field Observation to Estimate the Primary Production in the Destratification Process in North Japan Sea

Abstract

The authors started field observation mainly around the Musashi Bank in 2009, in connection with a planning of fishing ground development in the exclusive economic zone around Hokkaido. It considered the migration pathway of the larva of alaska pollack that was the target of the resource conservation. From the survey, it was found that the lack of the nutrient salt on the surface was not recovered in autumn. As a result, the primary production rate in summer was about 36.6 (mg-C/m²/day), the rate in autumn decreased to 29.04, and that in winter along the pathway was 95.4. It was suggested that Tsushima Warm Current along the Hokkaido coast prevented de-stratification in autumn and it caused the lack of the nutrient salt in the photic layer. Assuming enough nutrient salt for photosynthesis, the calculated rate increased up to about 102.3.