Spatiotemporal changes in fish assemblage structures in the Udara River, Amitori Bay, Iriomote Island

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  • 西表島網取湾のウダラ川における魚類群集構造
  • イリオモテジマモウシュワン ノ ウダラガワ ニ オケル ギョルイ グンシュウ コウゾウ

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Abstract

<p>Fish assemblage structures in estuarine and freshwater areas in the Udara River, Amitori Bay, Iriomote Island, were investigated by visual transect surveys from November 2012 to October 2013. In total, 58 species (26 families) in the estuaries and 12 species (4 families) in freshwater, all comprising native taxa, were observed during the study period. Mean numbers of estuarine species and individuals were significantly higher in the lower and middle estuaries than in the upper estuary, multi–dimensional scaling analysis revealing that fish species compositions clearly differed among each estuarine station. The distribution patterns of the dominant estuarine species (Neopomacentrus taeniurus and Fibramia amboinensis) and the catadromous species Kuhlia rupestris largely explained such spatial variation. The former two species were abundant in the lower and/or middle estuaries with high salinity, whereas the latter was abundant in the low–salinity upper estuary, suggesting that the salinity gradient may be a factor determining the estuarine fish assemblage. In contrast, the freshwater fish assemblages, largely dominated by small amphidromous gobies, such as Stiphodon percnopterygionus, showed neither spatial nor temporal variations, possibly due to the fact that several factors, including water flow and depth, being relatively stable in the freshwater area. The study suggested that the estuarine areas were essential habitats for marine, estuarine and amphidromous freshwater fishes in the river, and should be accorded a level of protection in keeping with a high priority for fish diversity conservation in the small rivers of the Ryukyu Islands.</p>

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