On the Fluctuation in the Sardine Catch of the Western Japan Sea-I

Surface Temperature, Chlorinity, and the Sardine Fishery

Abstract

An attemp has been made at throwing light on the relationship between the sardine fishing off Shimane Prefecture and hydrographical conditions such as surface temperature and chlorinity of water in this region of the Sea of Japan on the basis of data available for the period of 1949 to 1953. The following has become evident through the study.
1. Commercial fishing for large sized (oba) sardine, Sardinia melanosticta, in the western part of the Japan Sea starts in waters around the 100-meter bottom contour when surface temperature ranges from 17° to 18°C. and chlorinity from 18.8 to 19.0‰. The operation would come off season at the same temperature range with chlorinity increasing more than 19.2‰. The minimum temperature during the season is about 9°C.
2. These particular ranges of water temperature and chlorinity are supposed to contribute as a compound factor in duration of the fishing season as well as formation of the fishing grounds in the area.
3. Schools of the sardine generally take three different courses when approaching to the shore, as illustrated in Fig. 1. The earliest comes in along the northernmost access, while the later schools take the southern approaches.
4. As water temperature in the season lowers and tends to expand the fishing ground southerly much faster than the northward transport of high chlorinity water, one group of the fish goes down south, while the other swimming up north, with the sea between Takashima and Mish ?? m ?? as a boundary for the movement in both directions. The movement continues until the water temperature reaches a minimum of the range.
5. The fishing situation for sardine in the area off Shimane Prefecture would be likely affected by the development of low chlorinity water which occurs from year to year in the sea around the Oki Islands during the winter.