- 著者
-
宇田 道隆
- 出版者
- 公益社団法人 日本水産学会
- 雑誌
- 日本水産学会誌
- 巻号頁・発行日
- vol.2, no.3, pp.107-111, 1933
- 被引用文献数
-
5
The shoal of “Katuwo” [<i>Euthynnus vagans</i> (Lesson)] is often found associated with either sea-birds, drifting timbers, whales, sharks, or what not. The association with sea-birds or whales is almost clcaracteristic to the shoals of this fish found in the districts south to Prov. Bosyu, whereas the shoals associated with sharks are mostly distributed in the northern districts. Such difference of the distribution corresponds to that of oceanographical conditions, particularly of salinity (Figs. 1, 2 and Tab. 1).<br> The denseness of crowd and the degree of biting are represented quantitatively with the index-numbers <i>k</i> and <i>q</i> respectively (Tabs. 2 and 3), viz., <i>k</i>=<i>m</i>+0.1<i>n</i>/<i>m</i>+<i>n</i>, where m and n are the number of records of dense and thin crowds respectively, and <i>q</i>=3<i>p</i><sub>2</sub>+2<i>p</i><sub>1</sub>+<i>p</i><sub>0</sub>+0.5<i>p</i><sub>-1</sub>+0.1<i>p</i><sub>-2</sub>/<i>p</i><sub>2</sub>+<i>p</i><sub>1</sub>+<i>p</i><sub>0</sub>+<i>p</i><sub>-1</sub>+<i>p</i><sub>-2</sub>, where <i>p</i><sub>2</sub>, <i>p</i><sub>1</sub>, <i>p</i><sub>0</sub>, <i>p</i><sub>-1</sub> and <i>p</i><sub>-2</sub> are the mumber of records of very good, good, medium, poor and very poor biting respectively. The index-number of fishing value of a shoal defined by <i>N'</i>/<i>lt</i>. where <i>N'</i>, <i>l</i> and <i>t</i> are the total number of fishes angled, the numberof rods used and the duration of angling respectively, varies with the product <i>Kq</i> (Tab. 6). But, since <i>N'</i> is not exactly proportional to <i>t</i> (Tab. 5), the above-mentioned index number is only an approximate one.<br> The relation between the degree of biting of “Katuwo” and the quantity of the contents of their stomach (Tab. 4) seems to be explained by taking the time required for digestion into account.