航空観察によつて得られた流れ藻量からモジャコ資源量を推定する1つの試み-I

流れ藻の分布状態

抄録

The “mojako” is the juvenile of the yellowtail, Seriola quinqueradiata TEMMINCK et SCHLEGEL, ranging from 2 to 15 cm in fork length, which lives together with floating seaweeds during spring and early summer in the sea west of central Japan. Since some years ago, the “mojako” has been important as an seed fish for the yellowtail pisciculture. The annual catch of the “mojako” has been over ten million in number since 1962. Therefore, it has been hotly argued since some years ago whether such an excessive catch of the “mojako” may have an adverse effect on the adult stock of the fish.
In order to solve the question aforementioned, the systematic surveys and researches are being carried out on a large scale by some of the governmental fisheries research laboratories and the prefectural fisheries experimental stations located along the East China Sea and the Pacific Ocean.
This is the first report of the surveys made by means of aeroplane and vessels, describing the condition of distribution of the floating seaweeds in May of 1964 in the sea west of Kyushu and the region around the Osumi Islands. The courses taken by the aeroplane and the vessels are shown in Table 1 and Fig. 1.
Aerial observations were made from an aeroplane, flying at 1, 500 feet, and 172 ?? 203km/hour (176km/hour in mean). Nearly all of the floating seaweeds observed were photographed, and both the localities and the amount were marked on the map in symbols (Fig. 2), and also the time of observation and the number of the seaweeds were recorded in the form as shown in Table 2.
The results are summarized as follows:
1) Much floating seaweeds were observed, concentrically distributed along the current rips in the sea north of N 32°30', especially abundant in the Iki Passage and the near waters to the south of the Goto Islands. On the other hand, scarcely any floating seaweeds were found in the off-shore waters and in the main stream of the Tsushima Current.
2) In the sea south of N 31°, both the current rips and the floating seaweeds were rarely observed, presumably because the region was open.
3) From the aerial observation it was found that the brown seaweeds grow on the shallow waters around the islands located north of the Yaku-shima, but none was seen growing around the islands located south of Kutino-shima. Judging from this fact, it can be assumed that the origin of the floating seaweeds drifting along the west coast of Kyushu is not so distant, and that they are locally produced in the respective districts.