5:15 PM - 7:15 PM
[ACG53-P04] A Slow-Flowing Water Area as Fish Habitat in the Tokachi River Estuary, Hokkaido, Japan
Keywords:Slow-flowing water area, Wando, Nursery function, Feeding ground function, Benthic ecosystem
The slow-flowing part of a stream near the bank is called a wando in Japanese. Wandos that form in rivers are known as habitats for various aquatic organisms. Some wandos are artificially created. There are many studies on wandos; however, few such studies have addressed wandos in Hokkaido, which is a cold region in northern Japan. Since the Hokkaido Government and the Hokkaido Regional Development Bureau have been promoting projects for creating wandos in Hokkaido, it is important to clarify the structure of the ecosystem in wandos as basic information for the conservation and creation of such slow-flowing water areas.
To obtain knowledge on the structure of the ecosystem and the function of such slow-flowing water areas as feeding grounds for fish and to collect data on the physical environment, including the water temperature, salinity, and flow velocity of the wando in the Tokachi River estuary of Hokkaido, Japan, we conducted continuous observations on the physical features of that wando and surveys of fish and their stomach contents, phytoplankton and benthic microalgae as primary producers, zooplankton, and benthic fauna, which are considered as food for fish, during spring and summer.
The survey showed that in the slow-flowing water area, the salinity varied with the tide and was influenced by the water level of the Tokachi River, but that the predominant flora and fauna were freshwater species. Chlorophyll-a levels were higher in the sediment surface layer at the surveyed site than in the water column at the same site and were higher at the wando than at a site in the mainstream of the Tokachi River that was surveyed as a control. During the spring, more fish were caught at the surveyed wando than at the faster-flowing river site. The fish stomach contents were also found to contain dipterans, which were predominant among benthic fauna in the slow-flowing water area.
This study suggests that the slow-flowing water area that formed near the mouth of the Tokachi River functions as a habitat for fish and as a food supply area for fish due to the development of a benthic ecosystem. Through this study, the authors provide useful data that can be used as a reference for future river improvement projects that aim to preserve the river ecosystem at reaches near the wando that was surveyed in this study.
To obtain knowledge on the structure of the ecosystem and the function of such slow-flowing water areas as feeding grounds for fish and to collect data on the physical environment, including the water temperature, salinity, and flow velocity of the wando in the Tokachi River estuary of Hokkaido, Japan, we conducted continuous observations on the physical features of that wando and surveys of fish and their stomach contents, phytoplankton and benthic microalgae as primary producers, zooplankton, and benthic fauna, which are considered as food for fish, during spring and summer.
The survey showed that in the slow-flowing water area, the salinity varied with the tide and was influenced by the water level of the Tokachi River, but that the predominant flora and fauna were freshwater species. Chlorophyll-a levels were higher in the sediment surface layer at the surveyed site than in the water column at the same site and were higher at the wando than at a site in the mainstream of the Tokachi River that was surveyed as a control. During the spring, more fish were caught at the surveyed wando than at the faster-flowing river site. The fish stomach contents were also found to contain dipterans, which were predominant among benthic fauna in the slow-flowing water area.
This study suggests that the slow-flowing water area that formed near the mouth of the Tokachi River functions as a habitat for fish and as a food supply area for fish due to the development of a benthic ecosystem. Through this study, the authors provide useful data that can be used as a reference for future river improvement projects that aim to preserve the river ecosystem at reaches near the wando that was surveyed in this study.