過去80余年間（1895～1978）における諏訪湖の年間漁獲量およびその出荷金額高の経年変化 -諏訪湖漁業協同組合，其の他の資料による-

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(1) Lake Suwa is one of the Lakes which have the highest landing amount of commercial fishes per unit area in Japan. It is the shallow eutrophic lake located at the altitude 759 m in Nagano Prefecture in the central part of Japan. It has a maximum depth of 6.5 m, a mean depth of 4.1 m, a surface area of 13.3 km2 (1976) and a volume of 0.06 km3. In the recent twenty years the lake has been eutrophicating year and year, and water pollution has had the tendency of progressing. So that the awful water bloom of blue-green algae has come to appear every summer. (2) Increase periods of total fish yields of whole lake were seen from 1895 to 1900, 1917 to 1919, 1923 to 1928, 1933 to 1940 and 1962 to 1965 during the past eighty years (Fig.1). The values of their yields obtained before the Second World War when the fish yields remarakably increased were markedly higher than that of the post-war. During the war they indicated the lowest. Abundance periods of fish group were from 1923 to 1928, 1939 to 1940 and 1962 to 1965, those of mollusc group being 1926 to 1929 and 1933 to 1940, and those of shrimp from 1922 to 1927. (3) The highest value and the lowest one of total fish yields indicated 1,340 ton/fresh weight/whole lake in 1925 and 67 ton in 1945, those of fish group did 874 ton in 1934 and 49 ton in 1945, those of mollusc group 945 ton in 1934 and 18 ton in 1945, and those of shrimp 184 ton in 1922 and 0.001 ton in 1970 (Table 2). Except the term of 1933 to 1940 when the annual amounts of mollusc group were most abundant, the fish group yields occupied more than about 50% of total fish yields from 1905 to 1978, while those of mollusc and shrimp did less than about 40% and about 10% respectively. The highest values of these percentages showed 94% on fish group in 1973, 80% on mollusc group in 1933 and 24% on shrimp in 1922 (Table 3). (4) Carassius, Corbiculidae and shrimps were richly landed from 1905 to 1925, and then Hypomesus transplanted in 1915, Carassius, Cyprinus, Corbiculidae and Viviparidae were abundantly landed in the early period of the 1930S. Thereafter Unionidae transplanted were separatively rich from 1933 to 1940, and the shrimps had become very poor on and after 1928 up to date. During the term from the middle of the 1940S to the end the yields of all kinds of commercial fishes decreased. Since 1950, the yields of Hypomesus have gradually increased year and year, on the contrary other kinds of fishes and mollucs have decreased. Recently the landing amounts of Hypomesus have taken up about 70 % the total fish yield (Fig. 5, Fig. 8). (5) Total annual amounts of money for commercial fish yield of whole lake showed a gradual increase from 1895 to 1914, in the term of which the highest value and the lowest one were 68,470 yen in 1914 and 16,440 yen in 1895. Between 1917 and 1945, a high peak of amounts of money and low peak of those were seen. The former appeared from 1923 to 1928, the latter came out from 1940 to 1942, and the maximum value and the minimum one were 482,000 yen in 1925 and 63,000 yen in 1932. Since 1946 up to date they abruptly increased every year, and the highest showed 146,530,000 yen in 1978, and the lowest did 2,460,000 yen in 1946 (Fig. 11). (6) The amounts of money for fish group always occupied more than 65 % of total ones, and those of molluscs and shrimps did less than 20 %. The Difference of these percentages between fish group and both molluscs and shrimps have growed larger year and year. The highest value of fish group indicated 97 % in 1975, and those of molluscs and shrimps did 20 % in 1938 and 19 % in 1921 respectively. The percentage values of amount of money for Hypomesus yields have elevated in the course of years, but those of other kinds of fishes, molluscs and shrimps went down (Fig. 13, Fig. 18). (7) Generally speaking, a rising tendency with years was recognized in annual unit prices of every kind of fishes from 1905 to 1978. But a reduction in price occurred from 1926 to 1936, Showa depression days, in all commercial fishes. The cheap fishes landed in rich amount were Hypomesus, Parasilurus, Carassius, Cyprinus and Gobiidae, and the high priced fishes landed in small quantities being Oncorhynchus, Plecoglossus, Anguilla, Tribolodon, and Sarcocheilichthys. Molluscs were more inexpensive than fishes and shrimps: Corbiculidae were more expensive than Viviparidae, and Unionidae were the cheapest shells (Fig. 26, Fig. 27). (8) It was discussed that what influence had the transplantations of fishes and shells, the environmental changes of natural shore destructed with embankment, dredging and reclamation which were attempted to water purification, and the increment of landing amount of carps cultured in floating nets given upon the chronological fluctuations in annual fish yields.
信州大学理学部の論文
1980-03-31

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倉沢秀夫
東邦大学理学部生物学教室

過去80余年間（1895～1978）における諏訪湖の年間漁獲量およびその出荷金額高の経年変化 -諏訪湖漁業協同組合，其の他の資料による-

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