Population status and factors affecting local density of endangered Japanese freshwater pearl mussel, Margaritifera laevis, in Shubuto river basin, Hokkaido

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  • Terui Akira
    Department of Ecosystem Studies, Graduate School of Agricultural and Life Sciences, The University of Tokyo
  • Miyazaki Yusuke
    Department of Ecosystem Studies, Graduate School of Agricultural and Life Sciences, The University of Tokyo
  • Matsuzaki Shin-ichiro S.
    Environmental Biology Division, National Institute for Environmental Studies
  • Washitani Izumi
    Department of Ecosystem Studies, Graduate School of Agricultural and Life Sciences, The University of Tokyo

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  • 北海道朱太川水系におけるカワシンジュガイ個体群の現況と局所密度に影響する要因
  • ホッカイドウ シュタイカワミズケイ ニ オケル カワシンジュガイ コタイグン ノ ゲンキョウ ト キョクショ ミツド ニ エイキョウ スル ヨウイン

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Abstract

Population status and physicochemical factors affecting local density of endangered freshwater pearl mussels, Margaritifera laevis, in Shubuto river basin were investigated through measurements of local density and individual size of M. laevis, and environmental variables at 27 sites (including 324 quadrats: 0.5×0.5m). Proportions of small-sized juveniles were 34-100% depending on the reach, suggesting relatively high recruiting rates. Generalized linear mixed models (GLMMs) revealed that the local density is strongly affected positively by dissolved oxygen, %sand, and current velocity. Quadratic terms are also strong for two physical factors, %sand and water depth. The local density tended to be higher at quadrats with 9.30-10.2mg/l dissolved oxygen, 10-50% sand proportion, 0.2-0.6m water depth, and 0.05-0.30m/s current velocity. There were little differences in the factors affecting local density among three size classes (<20mm, 20-50mm, >50mm). Therefore, the local density was significantly higher at the river fringe with a combination of more suitable physical environment factors than middle of the river. These results suggest that artificial alteration of river fringe could have adverse influences on M. laevis population.

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