Futoshi Nakamura

Biodiversity cannot be conserved by nature reserves alone. There are a range of reasons such as the limited area of nature reserves and their lack of representativeness, which were highlighted more...

Habitat fragmentation in freshwater ecosystems severely hinders the reproduction of migratory aquatic species by obstructing their spawning migrations. Given the widespread presence of artificial barriers, strategically allocating restoration efforts based on the distribution of suitable spawning habitats is essential. As substrate particle size is a critical factor in determining spawning habitat for many freshwater fish species, mapping suitable spawning habitats for target species based on this factor can be an effective approach for prioritizing habitat restoration. In this study, we assessed the impact of habitat fragmentation on spawning habitats for anadromous salmonids and identified habitats that should be prioritized for restoration. We did so by predicting the median particle size of riverbed materials across Hokkaido Island, northern Japan, using a machine learning algorithm. In addition, we verified through field surveys whether the predicted particle size was related to the observed substrate coarseness, and whether salmonids were spawning in the identified spawning habitats. The median particle size was mainly explained by the average elevation of river segments and the mean slope of the upstream catchment area. Field validation confirmed that observed substrate coarseness was related to the median particle size, and salmonids predominantly spawned in the predicted spawning habitats at the river segment scale. Overlaying barrier data onto the spawning habitat map revealed that 68.12% of suitable spawning habitats on Hokkaido Island are isolated. These results demonstrate that predicting particle size is an effective approach to assessing the impacts of fragmentation on spawning habitats of anadromous salmonids at a broad scale, and that the majority of suitable habitats are fragmented. Based on these results, priority should be given to restoring connectivity in rivers where large portions of spawning habitats are isolated from anadromous salmonids.

Reversing biodiversity declines will require redesigning agricultural landscapes and their management. Farmland abandonment and intensification are emerging as major drivers of biodiversity changes, and their consequences vary widely from negative to positive among continents. Despite decades of research on agricultural biodiversity, no generalizable framework has been established to predict these variations globally, hindering the development of effective conservation strategies. Here, we combine broad-scale, multiseason avian field surveys across Japan with a global meta-analysis spanning four continents. In field surveys, we compared avian species richness among 2-ha plots in abandoned farmland (≤ 50 y since abandonment), traditional farmland, and intensive farmland, controlling for the surrounding land-use cover. We showed that the dominant functional group robustly explains the direction and strength of community-level responses to abandonment and intensification. When mature-habitat species comprise over 50% of communities, abandonment enhances species richness by over 240%, reaching levels comparable to natural wetlands. Abandoned farmlands hold the potential to offset past biodiversity declines and thus merit considerations for inclusion within the conservation area networks. Conversely, when disturbed-habitat species comprise more than 48% of communities, abandonment and intensification reduce species richness, underscoring the importance of biodiversity-friendly farming. This study provides a basis to understand how to address varied spatial variations in biodiversity responses to management and land-cover changes—a long-standing hurdle in conservation science. Complex bird diversity responses can be predicted globally by simply identifying the dominant functional group, thereby helping develop the most effective conservation strategies. Transferability beyond birds and across taxa should be evaluated empirically.

釧路湿原国立公園において実施されたエゾシカ捕獲が，広葉樹稚樹の被食および樹高成長に与える影響を明らかにするため，5年間の捕獲期を含む10年間にわたり稚樹群の追跡調査を行った。稚樹の被食および樹高成長に影響する要因として，樹高，樹種，積雪条件，場所，捕獲状況を用い，樹高成長の解析ではシカの被食の有無も考慮して，一般化線形混合モデルにより解析した。その結果，樹高が低く積雪が多い条件で被食されやすく，捕獲期では被食が抑制されたが，捕獲休止後は経過年数とともに被食が増加した。樹高成長は，シカに被食された場合に特に樹高の高い稚樹で減少し，捕獲休止後に成長量の低下が顕著だった。また，初期樹高が高い稚樹ほど樹高200 cmへの到達率が高く，100 cmを超えると到達確率が大きく増加した。このことから，樹高100 cm以上の稚樹が存在する条件下で一定期間捕獲を継続することにより，稚樹更新を促進できる可能性が示唆された。

Hatchery fish and their offspring (including hatchery‐wild hybrids) have lower reproductive success than wild fish. Thus, the straying of hatchery fish may negatively impact wild populations, depending on the number of wild salmon returning and hatchery strays. We investigated the straying status of hatchery‐origin pink salmon (Oncorhynchus gorbuscha), which have a higher straying rate than other salmonids, in an unstocked river at the Shiretoko World Natural Heritage Site, Japan. The hatchery strays accounted for 40.0% and 19.0% of the total samples in 2021 and 2022, respectively. These results indicate that hatchery pink salmon have invaded unstocked rivers and potentially genetically affect wild populations.

Increased flood magnitude and frequency due to climate change can reduce the population productivity of organisms such as amphibian and fish species in river and stream systems; therefore, conserving habitats that maintain high productivity under such conditions is crucial. Here, we examined the relationship between the freshwater productivity of anadromous salmonids (measured as fry migrating to the ocean per spawner) and catchment hydrogeomorphology and identified the characteristics of rivers and streams that are prone to flood disturbance. We surveyed the spawner abundance and number of fry of pink salmon (Oncorhynchus gorbuscha) and measured environmental factors, including the average catchment slope and stream power, as characteristics of hydrogeomorphology, in 10 streams in the Shiretoko Peninsula, northern Japan. We then used generalised linear mixed models to predict the freshwater productivity of pink salmon populations in each catchment across the study region under current and future climatic conditions. The productivity of pink salmon in the study region differed among the sampled catchments and was negatively affected by the average catchment slope, stream power, and maximum daily precipitation averaged over the catchment. Namely, flood disturbance reduced the freshwater productivity of pink salmon, and salmon productivity in individual catchments was explained by catchment hydrogeomorphology. The predicted future productivity with increased precipitation was also lower than the current productivity. Our approach can be applied to other salmonids that have similar spawning behaviour to pink salmon. Highly productive catchments under the future climatic conditions predicted by the present study should be prioritised for conservation to ensure a sustainable salmonid population.

The reproductive success of wild anadromous salmonid populations can be reduced by genetic interactions with straying hatchery fish. We investigated the straying status of hatchery-origin pink salmon (Oncorhynchus gorbuscha), which have a higher straying rate than other salmonids, in an unstocked river in the Shiretoko World Natural Heritage Site, Japan, which is a data-poor region. Hatchery strays accounted for 40.0% and 19.0% of the total samples in 2021 and 2022, respectively. These results indicate that hatchery pink salmon have invaded unstocked rivers and potentially genetically affect wild populations.