Estimation of the Catch of Autumn Chum Salmon in Otsuchi Bay in 1959

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  • 1959年の大槌湾における秋ザケ漁獲量の推定
  • 1959ネン ノ ダイツイワン ニ オケル アキ ザケ ギョカクリョウ ノ スイテイ

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Abstract

1) The catch of autumn chum salmon (Oncorhynchus keta) during 1959 season was estimated for 18 trap nets set in the Otsuchi Bay, Iwate Prefecture, northern Honshu (Fig. 1). Data were obtained from 10-day reports of daily catch submitted from each net. For the 10-day periods where reports were not available, statistics kept at the Otsuchi fish mar-ket were applied with correction by the mean percentage of the catch of each net sold at the market.<br> 2) The total number of fish caught from early October to late December amounted to about 20, 000. The catch in Otsuchi and Kotsuchi Rivers (escapement) in the same period was about 5, 000, which is about 20% of the total return. (Table 1).<br> 3) The percentage of the catch sold at the market varied from net to net, some having values of almost 100% and some almost zero. There was a trend for the percentage to decrease during the fishing season. (Fig. 2).<br> 4) There was a resemblance in the pattern of the seasonal change of the catch between adjacent nets (Fig. 3).<br> 5) Although in some cases the percentage sold at the market exceeded 100%, most of these ridiculous values occurred in the beginning or the end of the season and the catch in-volved formed only a negligible part of the total. And this inaccuracy would not negate the validity of the entire results.<br> 6) As no direct evidence was given to verify the reliability of the fishermen's reports, there may be a possibility of erroneous estimates. However, the above mentioned circum-stantial evidences suggested that the actual catches were represented fairly well in the re-ports.

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