びわ湖のホンモロコ個体群の年変動の解析 : I.生活環のどの位置が個体群の年変動に関係しているか

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タイトル別名
  • POPULATION STUDIES OF HONMOROKO, GNATHOPOGON CAERULESCENS SAUVAGE, IN LAKE BIWA, JAPAN. : I. ON THE CRITICAL LIFE-CYCLE STAGES RELATED TO THE ANNUAL FLUCTUATION OF THE POPULATION
  • びわ湖のホンモロコ個体群変動の解析-1-生活環のどの位置が個体群の年変動に関係しているか
  • ビワミズウミ ノ ホンモロコ コタイグン ヘンドウ ノ カイセキ 1 セイカツカン ノ ドノ イチ ガ コタイグン ノ ネン ヘンドウ ニ カンケイ シテ イル カ

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Gnathopogon caerulescens (Cyprinidae), about 10cm in body length of the adult, lives only in Lake Biwa, Japan. The main food of this fish consist of planktonic crustaceans. Seasonal migration of the fish was clearly observed : i.e. they are distributed in the hydrophyte area of the inner bay in spring, the bottom layer of the inshore part in summer and the bottom layer of the deepest part in winter. Records of daily catches by several fishing gears, namely a gill net, a trawl and a spawning trap, from 1957 to 1964 were available by the courtesy of the Fishermen Cooperative Associations which are situated around the lake for the estimation of the population density in the present study. Samples of adult or sub-adult were taken monthly from commercial fishing catches by the above mentioned gears between April 1964 and March 1966 and from these sampled specimens the age and other measurements concerning the population dynamics were measured or examined. The mean of the catch per day by the spawning trap in spring may be considered as the index of the spawner population. The main part of the population caught by the trawl in winter is the under-yearling, so that the mean of the catch per day may indicate the population of this stage. As the specimens caught by the gill net in summer consists mainly of the yearling, the mean of the catch per day may be used as the index of the yearling population in summer. The index of the under-yearling population between November and December tends to be proportional to that of the spawner population. From this fact it is suggested that, although there are many distinctive life cycle stages, egg, fry and juvenile, and these stages are supposed to be highly vulnerable, mortality in these stages give little effect on the annual fluctuation of the population density. There is no corelation between the index of the under-yearling population in early winter and that in late winter. Therefore, it is likely that the proportional relation between the size of the biomass of the spawner and their progeny is disordered during winter. So far as the present study goes it can be concluded that one of the causes for the annual fluctuation of the population density rests on the disorderliness between the size of the biomass in early winter and that in late winter. The index of the yearling population in summer seems either to be constant regardless of the yearly change of the index of the under-yearling population in late winter, or to show rather negative correlation with the latter index. Heavy fishing during the spawning season could have a negative effect on the increasing population.

収録刊行物

  • 日本生態学会誌

    日本生態学会誌 16 (5), 183-190, 1966

    一般社団法人 日本生態学会

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