Population Density and Growth of Unio douglasiae and Lanceolaria grayana (Bivalvia : Unionidae) in a Small Creek at Kyoto

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  • イシガイとトンガリササノハガイの個体群密度と成長
  • イシガイとトンガリササノハガイの個体群密度と成長(短報)〔英文〕
  • イシガイ ト トンガリササノハガイ ノ コタイグン ミツド ト セイチョウ タ

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Abstract

Population density and growth of Unio douglasiae and Lanceolaria grayana were studied by the mark-and-recapture method in a small creek from July 1987 to September 1988. Population of each species was stable and the estimated number of individuals per square meter was about 4 in U. douglasiae and about one in L. grayana. The pattern of seasonal growth was the same in both species. Growth was rapid in summer and in autumn, but retarded during winter. Although growth increment was small, about one-third of U. douglasiae grew in winter, while only one-tenth of L. grayana did. The yearly growth increment of each individual ranged between 0.7 mm and 5.3 mm in U. douglasiae, and between 0.6 mm and 6.7 mm in L. grayana. It was observed only a weak negative correlation between yearly growth increment and shell length in both species. Variation in the yearly growth increment among individuals of the same size may be due to the difference in the reproductive investment.

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