中海本庄水域におけるアサリの生残と成長 : 関連する要因の予察と潮通しパイプの効果の検討

Survival rate and growth 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 tidal flow pipes 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 the lake bottom of 3 stations; (1) Pipe-front in Honjo (2) Off-Eshima in Honjo and (3) West Channel around Honjo. Survival rate, growth 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. Survival rates of Pipe-front were higher than those of Off-Eshima, mainly because mass mortality occurred around off Eshima Island in the end of July. This event was observed as formation of anoxic and hydrosulfide-rich water layer, or masking of the surface that derived by concurrent death of sea algae, Cladophora speciosa. The water current through the tidal flow pipes appeared to make animals avoid the influence of the mortal event around them. Shell growth was apparently higher among individuals set on 1.5m depth than on 4m depth, for both Pipe-Front and Off-Eshima stations.