The Fluctuation in Fishing off Shimane Prefecture Viewed from the Recovery of Current Bottles Experiments

Abstract

During the perriod of 1923 to 1930 current bottle experiments were conducted every summer at several stations in the sea extending from 10 to 60 miles off Hamada, Shimane Prefecture as illu-strated in Fig. 1. It is obvious from Table 1 that the bottles liberated at Stations 4 and 5 in the sea more than 30 miles offshore tended to be transported by the ocean current to the northern regions. On the other hand, those which were released in the sea within 30 miles offshore were recovered on the coasts of either south or north of the Noto Peninsula, Ishikawa Prefecture, at different rates depending on the year. The fact may be interpreted to reveal that the course of the coastl current flowing northward closely along the shore devaited from year to year and possibly affected the migration of the littoral fish such as sardine, Sardinia melanosticta, and mackerel Scomber japonicus.
As far as data of the recovery indicates, the coastal current would often turn northeast at Hino-misaki and pass either along the outer periphery of the Oki Islands or through the straits between these islands. In the former case, fishing of large sized (oba) sardine comes into season later than usual with a fewer catch up to the end of the season. However, the same current movement in those years favored more than in other years the mackerel fishing operated by purse seines around and north of the Oki Islands. Beach seines and set nets in coastal waters had also greater catch than they did in the average season. However, angling and long line fisheries had fewer catch of mac-kerel probably because of greater supply of natural food for the fish. When the current passed through the Oki Straits, the line fisheries outnumbered the seiners in catch of the mackerel.