クシロガワリュウイキ ノ イトウ HUCHO PERRYI サンランカセン ニ オケル レキノイドウ キョウキュウ ニ カンスル チョウサケンキュウ

北海道東部の緩蛇行河川において,サケ科魚類イトウHucho perryiの産卵床は,蛇行区間の崖が洗掘され,堆積したと思われる河床の礫底に造成される傾向にある。そこで本研究においては,崖が存在する蛇行区間と崖が存在しない蛇行区間の物理環境を測定し,礫の供給が崖に依存しているか否かを調査した。結果,両蛇行区間の比較において,川幅,流速,半径に有意差はなかったが,水深は崖のある蛇行で有意に浅く,礫サイズも崖のある蛇行で有意に大きかった。また融雪増水時に投入した礫に移動が認められなかったことから,礫の供給は上流域からではなく崖が洗掘されることにより供給されるものと推定された。In eastern Hokkaido, Kushiro river basin where the redd of japanese huchen is observed, the river cliff eroded, and gravel accumulated. In this study, the physical environment was measured in order to examine just how the river precipice is the supply source of the gravel. As a result, no significant differences were indicated in the river width, velocity and the radius but the river depth in the meander with river cliff is significantly shallower than the one without river cliff and the size of gravel in the meander with cliff is significantly larger than the one without river cliff. Additionally, there was no obvious migration of gravel by freshet of snow melting. In conclusion, it was extrapolated that the gravel was provided not from upstream but by the eroding of the river cliff

クシロガワスイケイイチシリュウ ニ オケル イトウ HUCHO PERRYI ノ サンランセイタイ : 2006ネン ノ チョウサ ニ オケル サンランキカン サンランユカスウ オヨビ ソノ ブンプ ノ トクチョウ

2006年に北海道東部釧路川水系の一支流で,絶滅が危惧されている日本最大の淡水魚イトウ(Hucho perryi)の産卵生態調査をおこなった。調査において産卵期間は4月1日から5月7日までの37日間,産卵床は65床,水温は0.9-7.0℃を記録した。北海道中部や北部の河川において本種は4月下旬から産卵を開始し,産卵期間は7日から14日程度,産卵期の水温は3-7℃程度と報告されているが,北海道東部に位置する本研究の対象河川では,北海道中部や北部の河川よりも産卵開始日は3週間程度早く,産卵期間は長期であり,低い水温の時期から産卵していることが観察された。こうした特徴は,北海道中部や北部よりも降雪量が少ないこの地域特有の融雪期の気象条件や河川環境によるものであると推定された。The Sakhalin taimen, Hucho perry, is the biggest freshwater fish, and one of the endangered species in Japan. We studied reproductive ecology of this fish in one of the subsidiary streams of Kushiro River, eastern Hokkaido. In the study, the spawning period lasted for 37 days from April 1 to May 7. Redds were 65 and the water temperature was from 0.9 to 7.0 degrees Celsius. It is reported that this fish starts spawning at the end of April, the spawning period lasts for 7 to 14 days and the water temperature during spawning term is 3 to 7 degrees Celsius in the rivers in the middle and north of Hokkaido. However, in the river where we conducted this research in the east of Hokkaido, it was observed that the spawning of the fish started about three weeks, earlier than the fish in the rivers in the middle and north of Hokkaido that the spawning period was longer and that the spawning started when the water temperature was still low. It could be estimated that this is because the amount of snow in this area is comparatively small than that of the other areas and the climate conditions and river environment in the melting season differ

A challenge to dam improvement for the protection of both salmon and human livelihood in Shiretoko, Japan's third Natural Heritage Site

The Shiretoko Peninsula was placed on the World Heritage List in July 2005 as Japan's third Natural Heritage Site, being valued for its unique ecosystems formed by the interaction between marine and terrestrial environments. Prior to its listing, however, the International Union for Conservation of Nature and Natural Resources requested the development of measures to allow for the free movement of salmonids through the nominated area via artificial in-stream structures. This report introduces a pioneering effort to modify check dams in order to improve ecosystem linkages. The River Construction Working Group has intensively discussed and implemented restoration projects for three years, and the results have been monitored after implementation. Of 44 streams within the Shiretoko World Natural Heritage Site, 14 streams have had one or more in-stream structure(s) built. A total of 123 structures, mainly soil conservation dams, are distributed sporadically in these streams. Following assessment, the Working Group concluded that it would be reasonable to modify 31 structures in 5 streams, including 18 structures that were to be modified before listing. The most suitable design that met local stream conditions was selected, after accounting for salmon passage, adverse impacts on stream environments above and below the construction sites and on fishing grounds, efficiency of construction and ease of post-modification maintenance. Working in cooperation among the group members and parties concerned, we succeeded in restoring salmonids' upstream runs and extending their spawning habitat in streams above some of the dams, while keeping the disaster prevention function of the dams intact