Intraspecific and Interspecific Variations in Habitat Usage by Hemimyzon formosanus and Sinogastromyzon nantaiensis in Riffle Areas of a Mountain Stream

Abstract

In this study, we explored the structure of two migratory fish species and their variations along the longitudinal gradient of a stream by examining abiotic factors such as spatial scale elements and environmental factors, and biotic factors such as competition. The studied fish species, i.e., Hemimyzon formosanus and Sinogastromyzon nantaiensis, were sampled from the middle and upper reaches of the Nanzihsian Stream using the electrofishing technique, and data were collected on the physical environment covered by the electric grid. Statistical analyses confirmed that the interspecific and the intraspecific hydraulic habitat environments of the two species were different, i.e., H. formosanus was distributed relatively upstream and S. nantaiensis was distributed relatively downstream. Therefore, the habitat use of the two benthic fish species was different. The Nanzihsian Stream experienced an extreme flood event in 2009. The densities of adult and juvenile H. formosanus and S. nantaiensis are significantly higher than those before the extreme flood event in 2021, so we suggest that the H. formosanus and S. nantaiensis populations have recovered to those of the stages before the extreme flood event. We provide an integrated approach for applying engineering and biology to the context of future projects involving river dredging after extreme floods.