Spawning redds selection of Arctic lamprey <i>Lethenteron japonicum</i> in the Ishikari River

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  • SHIRAKAWA Hokuto
    <I>Graduate School of Fisheries Sciences, Hokkaido University</I>
  • YANAI Seiji
    <I>Department of Environmental Science, Ishikawa Prefectural University</I>
  • GOTO Akira
    <I>Graduate School of Fisheries Sciences, Hokkaido University</I>

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Other Title
  • 石狩川におけるカワヤツメの産卵場選択
  • イシカリガワ ニ オケル カワヤツメ ノ サンランジョウ センタク

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Abstract

We examined spawning preference of the Arctic lamprey Lethenteron japonicum in order to establish an effective conservation measures for the critically endangered natural populations. Investigations were carried out in the Oshirarika River. The spatial distribution of spawning site was monitored by DGPS and environmental variables (current velocity, substrate composition and water depth) were measured at each spawning redds in 2005, 2006 and 2009. The generalized additive models (GAM) were employed to extract a determinant variable for presence / absence of spawning redds. The spawning redds were made at water depths between 35 and 60 cm, and current velocity between 25 and 70 cm/s, with cobbles of 10 cm in diameter according to field observation. Spatial distribution of spawning redds differed by each research year, but they tent to show aggregate distribution. Water depths were a significant factor to determine the location of spawning redds throughout the three years, but current velocity was the only significant in 2006. The GAM analysis demonstrated that critical environmental factors influencing on spawning redds of L.japonicum was water depth, especially with 35-50 cm depth. Since water level of Oshirarika River decreases rapidly from May to July after snow-melt (decreasing 25 cm in two weeks). Our results suggest an adaptive behavior that L.japonicum selects to spawn in medium water depth in order to prevent the depth of fertilized eggs by dry during water discharge decreasing periods.

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