Although recreational fishing is popular in Japan, few estimates have been made of its economic value to the country. This study aims to (1) evaluate the economic value of recreational fishing in ...Tango Bay, Kyoto Prefecture using the travel cost method (TCM); and (2) explore the development of related regional economies around Tango Bay. The TCM analysis showed that 150,000 anglers visit Tango Bay annually, and the estimated total annual travel cost and total annual consumer surplus of recreational fishing there are approximately JPY 3.8 billion and JPY 11.7 billion, respectively. The annual commercial fisheries production of Kyoto Prefecture in 2017 was JPY 3.0 billion. Thus, in Tango Bay, coastal fish resources not only have a direct use value as food, but also a large indirect value as targets for recreational fishing. The importance of recreational fishing relative to commercial fishing has increased in Japan similar to in other countries where it is popular. As many people enjoy recreational fishing in Japan, it is expected to have an impact on domestic fish resources. To address this, both commercial and recreational fishing should be included in fish resource management activities aimed at the development of related local economies in Japan.
Biodiversity is an important parameter for the evaluation of the extant environmental conditions. Here, we used environmental DNA (eDNA) metabarcoding to investigate fish biodiversity in five ...different estuaries in Japan. Water samples for eDNA were collected from river mouths and adjacent coastal areas of two estuaries with high degrees of development (the Tama and Miya Rivers) and three estuaries with relatively low degrees of development (the Aka, Takatsu, and Sendai Rivers). A total of 182 fish species across 67 families were detected. Among them, 11 species occurred in all the rivers studied. Rare fishes including endangered species were successfully detected in rich natural rivers. Biodiversity was the highest in the Sendai River and lowest in the Tama River, reflecting the degree of human development along each river. Even though nutrient concentration was low in both the Aka and Sendai Rivers, the latter exhibited greater diversity, including many tropical or subtropical species, owing to its more southern location. Species composition detected by eDNA varied among rivers, reflecting the distribution and migration of fishes. Our results are in accordance with the ecology of each fish species and environmental conditions of each river.
Japanese eels (
Anguilla japonica
) utilize a broad range of habitats along the marine-freshwater ecotone during their growth phase in inland waters. This study aimed to analyze the foraging behavior ...of yellow-phase Japanese eels in connected fresh- and brackish water habitats and to connect foraging behavior and habitat use through the analysis of carbon (
δ
13
C) and nitrogen (
δ
15
N) stable isotopes. Stomach contents of eels collected in fresh- and brackish waters were analyzed to identify food sources. Values of
δ
13
C and
δ
15
N were analyzed in eels and their potential food sources, and used to predict the recent foraging patterns of eels in the Matsukawa-ura, a brackish water lagoon, and in three freshwater tributaries. Eels preyed on the benthic river community and the mudflat community of the lagoon. Gobiid fishes were found to be an important food source for eels in fresh- and brackish water habitats, while Japanese mitten crabs (
Eriocheir japonica
) and shore crabs (
Hemigrapsus
spp.) were major prey in fresh- and brackish waters respectively.
δ
13
C values of potential eel prey differed significantly between fresh- and brackish waters and were used to classify three recent patterns of foraging by the 73 eels included in this study: 1) freshwater foraging, 2) brackish water foraging, and 3) multiple-habitat foraging. The data suggested that some eels recently or frequently moved between fresh- and brackish water habitats while others demonstrated a higher fidelity to either fresh- or brackish waters. Isotopic characteristics of prey in the respective foraging habitats revealed the plasticity of habitat use of yellow eels in the study area. This study demonstrates an integrated approach to study habitat use and foraging behavior of eels. Furthermore, the study underlines the need to consider freshwater and estuarine habitats and the connectivity between them for eel management and conservation.
Japanese eel (
Anguilla japonica
) is a commercially important species; however, its population has declined in recent years. Appropriate conservation management, including habitat protection, is ...required to reverse this decline. However, their habitat use pattern during the riverine life stage is poorly understood. In this study, we investigated the longitudinal distribution and microhabitat of small-sized (<200 mm total length) and large-sized (≥200 mm total length) Japanese eels observed in 83 and 124 quadrats (1 m × 1 m), respectively, placed at seven stations in the Nikkeshi River in Fukushima Prefecture, Japan. Analysis using generalized linear models revealed that the eel density of both size classes decreased with increasing distance from the river mouth. In addition, the density of small-sized eels, but not large-sized ones, decreased as weir numbers increased. Moreover, analysis using generalized additive models showed that microhabitat uses differed between the size classes. The small-sized eels used near-shore habitats which had low current velocities. Their preferred habitats contained both complex substrates with smaller particle sizes and simple substrates with relatively large particle sizes. In contrast, the large-sized eels used both near-shore habitats with lower current velocities and the center of the river which had high current velocities. They preferred simple riverbed habitats with large particle-sized substrates and no underwater vegetation. These results suggest that there is a size-dependent change in the longitudinal distribution and microhabitat use of Japanese eels during their river life stage. These findings provide valuable information for the conservation and management of Japanese eels in rivers.
Yellow-phase Japanese eel
Anguilla japonica
(Temminck & Schlegel, 1846) utilize a variety of anthropogenically impacted habitats. An extensive understanding of the trophic ecology and habitat use is ...necessary for the conservation of this endangered species. In this study, we analysed the trophic ecology and feeding habitat of Japanese eels in two small rivers, the Akugawa River and Takase River in Wakayama Prefecture, Japan, dominated by an urban landscape and agricultural land use, respectively. The main goals were to assess the dietary diversity and trophic niche width for eels of two size classes (small eels: ≤ 240 mm total length, large eels: > 240 mm total length) in both habitats. The suitability of both rivers as a feeding habitat for eels was also evaluated. The trophic ecology of eels was inferred based on analysis of carbon and nitrogen stable isotopes, as well as stomach contents. Our results indicated that both rivers are suitable habitats to accommodate this eel, but to varying degrees. The dietary diversity of small eels and trophic niche width differed between rivers, indicating limiting factors, such as insufficient food sources and unfavourable abiotic habitat requirements for small eels in urban rivers. Also, the body condition of eels was found to be lower in the urban Akugawa River than in the Takase River.
•Environmental DNA metabarcoding detects rare, endangered, and alien species in estuarine and coastal fish communities.•Latitudinal effect is found in estuarine and coastal fish communities across ...Japan.•Bank artificialisation negatively impacts estuarine and coastal fish community structures.•Ocean currents weakly affect estuarine and coastal fish community structures.•Environmental DNA metabarcoding is useful for large-scale assessing fish communities in estuaries and coasts.
Estuarine and coastal ecosystems are important habitats for many fish species. Large-scale patterns of estuarine and coastal fish communities can be affected by geographical factors, such as water temperature and latitude, that limit or allow fish dispersal, and/or by environmental factors that select locally adapted species. Furthermore, increased human activity has also altered fish diversity by modifying estuarine/coastal environments. Here, we used environmental DNA metabarcoding to study a large-scale pattern of estuarine/coastal fish communities across 25 watersheds in the Japanese Archipelago, and we assessed the effects of geographical, environmental, and anthropogenic factors in structuring these communities. Of the 290 fish species detected, 47 species were red-listed by the Japanese Ministry of Environment, and nine were alien. Non-metric multidimensional scaling showed that latitude and water temperature affected both river-mouth and coastal-sea fish communities. Although other anthropogenic factors did not affect these communities, bank artificialisation rates influenced both. The relationship between each fish community and ocean currents was weak. The number of red-listed fish affected both fish community structures, whereas that of alien species did not. The numbers of red-listed fish in coastal points and of all fish species were negatively influenced to the human population density. These findings provide useful information that may be used to conserve estuarine and coastal ecosystems.
Estuaries––one of the most vulnerable ecosystems globally––face anthropogenic threats, including biodiversity loss and the collapse of sustainable fisheries. Determining the factors contributing to ...the maintenance of estuarine biodiversity, especially that of fish, is vital for promoting estuarine conservation and sustainability. We used environmental DNA metabarcoding analysis to determine fish species composition in 22 estuaries around Japan and measured watershed‐scale land‐use factors (e.g., population size, urban area percentage, and forest area percentage). We sought to test the hypothesis that the richness of the most vulnerable estuarine fish species (i.e., registered by the Japanese Ministry of the Environment in the national species red‐list) is determined by watershed‐scale land‐use factors. The richness of such species was greater, where forest cover was highest; thus, forest cover contributes to their conservation. The proportion of agriculture cover was associated with low species richness of red‐listed fishes (redundancy analysis, adjusted R2 = 43.9% of total variance, df = 5, F = 5.3843, p = 0.0001). The number of red‐listed species increased from 3 to 11 along a watershed land‐use gradient ranging from a high proportion of agriculture cover to a large proportion of forest cover. Furthermore, the results showed that throughout Japan all the examined watersheds that were covered by >74.8% forest had more than the average (6.7 species per site) richness of red‐listed fish species. This result can be attributed to the already high average forest cover in Japan of 67.2%. Our results demonstrate how the land use of watersheds can affect the coastal sea environment and its biodiversity and suggest that proper forest management in conjunction with land‐use management may be of prime importance for threatened fish species and coastal ecosystems in general.
Efectos de la Cobertura Forestal sobre la Riqueza de Especies Amenazadas de Peces en Japón
Resumen
Los estuarios—uno de los ecosistemas más vulnerables a nivel mundial—enfrentan amenazas causadas por el hombre, incluyendo la pérdida de biodiversidad y el colapso de las pesquerías sustentables. La determinación de los factores que contribuyen al mantenimiento de la biodiversidad estuarina, especialmente la de los peces, es vital para fomentar la conservación y sustentabilidad estuarinas. Usamos un análisis de metasecuenciación de ADN ambiental para determinar la composición de especies de peces en 22 estuarios de Japón y medimos los factores del uso de suelo a nivel de cuenca (p. ej.: tamaño poblacional, porcentaje de área urbana y porcentaje de área forestal). Buscamos probar la hipótesis de que la riqueza de las especies de peces más vulnerables (es decir, aquellas registradas por el Ministerio Japonés del Ambiente en la lista roja de especies a nivel nacional) está determinada por los factores de uso de suelo a nivel de cuenca. La riqueza de dichas especies fue mayor en donde la cobertura forestal era la más alta; por lo tanto, la cobertura forestal contribuye a la conservación de estas especies. La proporción de la cobertura agrícola estuvo asociada con una baja riqueza de especies de peces en la lista roja (análisis de redundancia, R2 ajustada = 43.9% de la varianza total, gl = 5, F = 5.3843, p = 0.0001). El número de especies en la lista roja incrementó de 3 a 11 a lo largo del gradiente de uso de suelo de la cuenca, yendo desde una proporción alta de cobertura agrícola a una proporción alta de cobertura forestal. Además, los resultados mostraron que, en Japón, todas las cuencas analizadas que contaban con una cobertura forestal >74.8% tenían mayor riqueza de especies de peces en la lista roja que el promedio (6.7 especies por sitio). Este resultado puede atribuirse a la ya de por sí elevada cobertura forestal de Japón (67.2%). Nuestros resultados demuestran cómo el uso de las cuencas puede afectar al ambiente costero marino y a su biodiversidad y sugiere que la gestión adecuada de los bosques en conjunto con el manejo del uso de suelo puede ser de suma importancia para las especies amenazadas de peces y los ecosistemas costeros en general.
Article impact statement: Agricultural and forest cover have opposite effects on the richness of red‐listed fish species in Japanese estuaries.
Eel movement patterns have been frequently studied to learn about their movements within the fresh- and brackish waters of the same river before their spawning migrations. Although otolith ...microchemistry analyses estimated that the eels used fresh-, brackish, and marine water habitats, inter-river movements of Japanese eels via the sea have not been observed. In previous studies silver eels appear to migrate for spawning in October-December, and so eels that migrate to the sea during this period have been considered as migrating for spawning. In the progress of our acoustic telemetry study on eel movement patterns, we found the first evidence that Japanese eels move between distant rivers via the sea. During the study in the Akugawa River, Wakayama Prefecture, Japan, we released 15 acoustically tagged yellow-phase eels on 8 April 2019. Three of the 15 tagged eels released into the Akugawa River were later caught in the ~ 15 km distant Hidari-Aizu River by a local angler during early mid-July 2020. This showed that 2 of 3 tagged eels migrated seaward in October and December. The other tagged eel had been detected only at a releasing point until 30 June 2019 and due to an unknown reason was never detected again before capture in the Hidari-Aizu River. The remaining 12 tagged eels stayed in the Akugawa River during the study period. These findings indicate that Japanese eels may migrate seaward for purposes other than just spawning. This information is valuable for understanding the eels’ life-history diversity and for future conservation plans.
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