- 著者
-
川尻 稔
- 出版者
- 公益社団法人 日本水産学会
- 雑誌
- 日本水産学会誌 (ISSN:00215392)
- 巻号頁・発行日
- vol.17, no.7, pp.206-210_2, 1952
The catch of <i>Tribolodon hakonensis</i> has shown a great decrease recently in Chikuma River, middle Japan. From the fact that many young fishes have been caught by the “Ishizuka”, Nagano Prefectural Government prohibited this particular gear since 1946, however, there were heard varied opinions among fishermen as to its effect and, as the result, to remove the regulation.<br> The “Ishizuka”, set up in early winter, is a mound composed of stones as, large as or larger thna humna head, measuring 50cm high and 100 to 150cm in diameter at bottom, the mound is built in the water 70 to 80cm deep with graduated slope toward the mainfolow of the river, also the entire “Ishizuka” is covered with straw-mat except the sloped part where the stones are flattened mixed with smaller gravels. In early spring, the mound is surrounded by bamboo-blinds and a trap is set against sloped part, then the stones are picked up piece by piece. The fish, mostly <i>T. hakonensis</i>, which conceal themselves in the space of stones during the winter, escape the mound and are easily trapped.<br> Experimental “Ishizuka” numbering 17 were set in November 1948-'49, and the fish 4699 caught following spring were studied on age and length. The age determination by scale on these fish showed 59.5% of one year old, 19.8% of two, 16.6% of three and other older. It is thus apparent that the “Ishizuka” destroys tie younger generation of fish.<br> 1 propose to regulate strictly the fishing by “Ishizuka” but rather utilize the mound for the protection of young by the hand of fishermen.