5:15 PM - 6:45 PM
[ACG39-P03] Changes in the number of Cherry salmon (Oncorhynchus masou) runs and improvement of fish passage in the small stream in Sapporo, Japan.
Keywords:urban stream , portable fishway, spawning behavior, carcass nutrient
Post-spawning salmon carcasses are an essential source of nutrients for river ecosystems, providing food for aquatic invertebrates and animals. In the Shojingawa stream, which flows through Sapporo City, juvenile Cherry salmon have been released since 1998. During the spawning season, the fish can be seen running upstream, and the salmon carcasses are also utilized by birds. Although a stairway fish passage was installed at the confluence of the Shojingawa stream and the Toyohira River over 50 years ago, it was not conducive to anadromous fish migration upstream. Therefore, the fish passage was improved in 2022. In Japan, fish counters have been increasingly utilized in fish passages to automate fish migration measurement, owing to the ease of installing counter sensors. It has been observed that in certain instances, a portable fishway and a fish counter have been utilized in conjunction to automatically measure run counts in natural rivers. Nevertheless, it appears that such instances are still infrequently documented. This study examines the potential effects of fish passage improvement on the number of Cherry salmon runs in the Shojingawa stream, which flows through Sapporo City.
Data was collected during the September-October run in 2022 and 2023 using a fish counter and a portable fishway made of track sheets. The study measured the number of Cherry salmon runs before and after fish passage improvements downstream of the portable fishway.
The results indicate an increase in the number of runs after the improvements. However, it is worth noting that the measurement period in 2023 was 10 days longer than in 2022. Therefore, the number of runs, excluding that period, was almost the same in both years. In the Toyohira River basin, where the Shojingawa stream flows, the number of Cherry salmon spawning beds was higher than usual in 2022, but decreased to the same level as usual in 2023. It is assumed that the increasing or decreasing number of spawning beds reflects the number of runs, since the spawning environment remained unchanged during these two years. The stable number of fish returning to the Shojingawa stream, despite a decrease in the number of fish returning to the watershed, suggests that the improvement of fish passage near the confluence may have contributed to the increase in the number of Cherry salmon returning to the Shojingawa stream. It is possible that the fish passage improvements may have contributed to the increase in the number of runs. In streams that have been degraded, enhancing fish passages such as this one can lead to an increase in the number of anadromous fish runs and help to maintain the nutrient-supply function of the upstream ecosystem for anadromous fish.
Data was collected during the September-October run in 2022 and 2023 using a fish counter and a portable fishway made of track sheets. The study measured the number of Cherry salmon runs before and after fish passage improvements downstream of the portable fishway.
The results indicate an increase in the number of runs after the improvements. However, it is worth noting that the measurement period in 2023 was 10 days longer than in 2022. Therefore, the number of runs, excluding that period, was almost the same in both years. In the Toyohira River basin, where the Shojingawa stream flows, the number of Cherry salmon spawning beds was higher than usual in 2022, but decreased to the same level as usual in 2023. It is assumed that the increasing or decreasing number of spawning beds reflects the number of runs, since the spawning environment remained unchanged during these two years. The stable number of fish returning to the Shojingawa stream, despite a decrease in the number of fish returning to the watershed, suggests that the improvement of fish passage near the confluence may have contributed to the increase in the number of Cherry salmon returning to the Shojingawa stream. It is possible that the fish passage improvements may have contributed to the increase in the number of runs. In streams that have been degraded, enhancing fish passages such as this one can lead to an increase in the number of anadromous fish runs and help to maintain the nutrient-supply function of the upstream ecosystem for anadromous fish.