Influence of Environmental Factors on Fish Fauna Distribution in Hill-bottom Valleys

Case study of the upper stream of the Kokai River

Abstract

In order to grasp distribution characteristics of fish fauna, field investigation was carried out in five hill-bottom valleys located in the upper stream of the Kokai River, Tochigi prefecture. The results obtained by the investigation were as follows: 1) A dense populated zone of Hotokedojyo was identified at Tanigashira, upper reaches of hill-bottom valley, 2) similarly, a dense populated zone of Numamutsu and Simadojyo was found at Tanijiri, lower reaches of hill-bottom valley, 3) on the contrary, dispersive distribution in the central area of the hill-bottom valley was found for Dojyo and Tamoroko. The results of correlation analysis showed a significant level relationship (p<0.01, p<0.05) between fish abundance of the surveyed station and ditch distance from Tanigashira to the surveyed station for Hotokedojyo, Simadojyo and Numamutsu. In terms of environmental factors, a negative correlation was found between fish abundance and water temperature on Hotokedojyo, a positive correlation between fish abundance and water temperature on Simadojyo, and a positive correlation between fish abundance and decrease in accumulated height of weir on Numamutsu as well.