中海・本庄工区におけるアサリの成長と生残に及ぼす潮通しの効果

その他

Growth and survival rate were examined for adult Ruditapes philippinarum in Honjo Area of Lake Nakaumi. This area is a brackish lake enclosed by embankments built for reclamation. Two pipes for sea-water induction of 2.5m in diameter were constructed on March 1998, to investigate potential of fishery promotion. Containers carrying 50 individuals of Ruditapes each were set on lake bottom of 2 stations ; (1) Pipe-Front in Honjo and (2) Off-Eshima in Honjo Area. Growth, Survival rate and water quality (temperature, salinity, dissolved oxygen) were examined between 1.5m and 4m in water depth for these stations, from June 4 to November 5 in 1998. Shell growth is apparently higher among individuals set on 1.5m depth than on 4m depth, for both Pipe-Front and Off- Eshima stations. This low growth on 4m depth was supposed to be derived from combined factors such as lower dissolved oxygen, lower food supply, lower water current effect and so on. Mass mortality occurred around off Eshima Island in the end of July. This event was derived by concurrent death of sea algae, Cladofphora speciosa. The water current through the induction pipes appears to make better environment for animals enough to ayoid the influence of this mortal event. However the pipes could not avoid the low growth of Ruditapes on 4m depth.