Multi-scale Spatial Analysis Of Physical Habitat Of Pseudobagrus ichikawai (Siluriformes: Bagridae) In Third Order Stream Landscapes, Mie Prefecture, Japan

* Tashiro, T (tasiro55@pwri.go.jp) , Aqua Restoration Research Center, Public Works Research Institute, Kawashimakasada-machi, Kakamigahara 501-6021, Gifu Prefecture, Japan, Kakamigahara, 501-6021 Japan Sagawa, S (ss1121@docon.jp) , Docon Co., Ltd., 1-5-4-1 Atubetsu-chuuou, Atsbetu-ku, Sapporo 004-0051, Hokkaido, Japan, Sapporo, 004-0051 Japan Kayaba, Y (y-kayaba@pwri.go.jp) , Aqua Restoration Research Center, Public Works Research Institute, Kawashimakasada-machi, Kakamigahara 501-6021, Gifu Prefecture, Japan, Kakamigahara, 501-6021 Japan Saiki, M (cde62220@hkg.odn.ne.jp) , Chubu Technical and Engineering Office, Ministry of Land, Infrastructure and Transform, 1-1-15 Taiko-minami, Higashi-ku, Nagoya 461-0047, Aichi Prefecture, Japan, Nagoya, 461-0047 Japan Hasegawa, K (hasega44@pwri.go.jp) , Aqua Restoration Research Center, Public Works Research Institute, Kawashimakasada-machi, Kakamigahara 501-6021, Gifu Prefecture, Japan, Kakamigahara, 501-6021 Japan Amano, K (amano@pwri.go.jp) , Public Works Research Institute, 1-6 Minamihara, Tsukuba 305-8516, Ibaraki Prefecture, Japan, Tsukuba, 305-8516 Japan

The bagrid catfish, Pseudobagrus ichikawai, is threatened with extinction, occurring only in the rivers flowing into Ise and Mikawa Bays. P. ichikawai is perceived to use the interstices of boulder clusters in backwaters. However, its ecology remains unclear owing to its nocturnal habits and unique habitat features. Recently, several river improvement works for controlling floods such as bank revetment, channel shortening and dam construction have decreased such environments in many rivers, and have also been considered to cause the reduction of catfish populations. The conservation of the remaining populations is fundamental not only for preserving species / genetic diversity, but also for sustaining the river landscape with its various environments. In other words, P. ichikawai can be utilized as an indicator species for this original river landscape. Therefore, in order to conserve a tiny population of the catfish, habitat restorations are planned in the 3rd order stream, a small branch of the Inabe River system in Mie Prefecture. The objectives of this study are to clarify the physical characteristics of P. ichikawai habitats and to help implementing habitat restoration in this small branch. This study consists of stratified analysis from the viewpoints of three kinds of spatial scale as follows: (1) landscape scale which includes physical land shape characteristics of the valley with each stream investigated before, (2) reach scale of the longitudinal 100 m length including the riparian zone with the multiple observed points of catfish and (3) micro-habitat scale of the quadrates (2m X 2m) where we observed the catfish individuals. At first, cluster analysis for scale (1) was conducted using variables such as sinuosity of channel, channel / valley width, and longitudinal / cross-sectional valley gradient. These parameters were obtained from general topographic maps and the 3rd order streams where local P. icihikawai populations survived in Mie Prefecture were covered in this analysis. The clustering determined one stream of the Miya River system as the reference stream. Thus, field investigations in scales (2) and (3) were conducted in both the target and reference streams. The inhabitation research for the P. ichikawai individuals with observation by snorkeling was carried out in the two streams at the beginning of the investigation. And then, the physical parameters (velocity, water depth, substrata and so on) were measured not only in the micro-habitat (3), but also in the reach scale (2). Furthermore, the topographic surveys in scale (2) were also exploited. According to these analyses, the individuals of P. ichikawai hided in the interstices of loose boulder clusters in backwaters during daytime. Particularly, this tendency became notable as they grew and gathered. In addition, the potential habitat area of catfish could be simulated in both streams, and thereby the difference of habitat conditions was quantitatively revealed. These results can be beneficial for rehabilitating the habitat of endangered bagrid catfish, P. ichikawai.

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