Identification of Critical and Tolerable Fish Habitat Requirements Based on Pre- and Post-Typhoon Data

Catastrophic typhoons with heavy rainfall introduce massive flow and fine sediments into stream channels. In addition, the natural disturbances and engineering practices afterward may strongly alter the fish abundance and their environment. This study compared physical habitat parameters and fish abundance before and after two major typhoons using two sampling period datasets (November 2008–March 2009 and May 2011–March 2012). The study area was in the Cishan Stream, a tributary of the Gaoping River in southern Taiwan. This area experienced two strong typhoons (Morakot and Fanapi) between the two sampling periods, providing an opportunity to compare pre- and post-typhoon conditions. The collected species were Hemimyzon formosanus, Rhinogobius nantaiensis, Onychostoma alticorpus, Candidia barbata, Acrossocheilus paradoxus, and Spinibarbus hollandi. Our results show a decrease in substrate size, fish size, and fish weight after typhoons. The river channel transformed into an unstable condition after the heavy rains, as major habitat types in our sampling stations changed from riffles with coarse substrate to runs with fine substrate. The results of statistical tests indicate the different habitat requirements of three major fish species (H. formosanus, R. nantaiensis, and O. alticorpus) and can indicate whether species’ requirements change between the two sampling periods. Water depth and pebbles were critical habitat requirements for the adults of H. formosanus; water depth, pebbles, and sand were critical habitat requirements for the adults of R. nantaiensis; and flow velocity and standard deviation of flow velocity were critical requirements for the juveniles of O. alticorpus. Understanding habitat requirements can provide useful information for post-disaster restoration and contribute to eco-sensitive river engineering.