Terrestrial invertebrates falling from the riparian canopy are a major energy source for fishes in headwater streams. Because quantity and quality of such allochthonous resources can vary depending on riparian conditions, conversion of riparian forests to conifer plantations may affect stream productivity. We compared falling and drifting invertebrate abundances and the diet of masu salmon (Oncorhynchus masou) among stream reaches bordered by deciduous broadleaved forests, conifer plantations (Cryptomeria japonica), and clear‐cut sites in southwestern Japan. We also examined whether among‐reach variation in salmon abundance was related to the riparian vegetation types. The results indicated that, on an annual basis, falling inputs of terrestrial invertebrates at the broadleaved reaches were 2–4 times higher than those at the plantation and clear‐cut reaches. In nonwinter seasons, terrestrial invertebrates made up 40–60% and 30–90% of drift and masu salmon diets, respectively, and drifting invertebrate abundance was higher in the broadleaved reaches than in the plantation reaches. Furthermore, a multivariate analysis of salmon abundance showed that variation in salmon biomass was explained primarily by riparian vegetation type, with broadleaved and clear‐cut reaches having higher biomass than the plantation reaches. These results indicate that terrestrial invertebrates are an important resource for masu salmon, and suggest that streams bordered by conifer plantations receive lower terrestrial prey inputs, which results in lower salmon abundance. In regions where natural forests have been extensively converted to conifer plantations, forest management that allows and facilitates recovery of natural riparian stands is important.
During spawning activity, fish release large amounts of sperm and eggs into the water, which has been assumed to cause an increase in environmental DNA (eDNA) levels and nuclear DNA/mitochondrial DNA ratios. To test whether these assumptions are valid and whether nuclear and mitochondrial eDNA analysis can be used to monitor the spawning activity of freshwater fish, we conducted field eDNA surveys and traditional surveys using common carp (Cyprinus carpio), largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) as model species. Fish spawning periods were estimated based on age, as estimated using the body lengths of juveniles collected in the Miharu reservoir in Fukushima, Japan. The results showed that the main spawning periods of largemouth bass and bluegill sunfish were from April to July and from July to August, respectively. Field eDNA surveys were conducted in the Hebisawagawa front reservoir, which is connected to the Miharu reservoir. From March to August 2019 and 2020, weekly eDNA sampling was conducted at three sites, and daily sampling was conducted at six sites from 23 June to 3 July 2020. The eDNA concentrations of the nuclear internal transcribed spacer 1 (ITS1) and mitochondrial cytochrome B (CytB), as well as the ITS1/CytB ratio, were measured for each of the three fish in each water sample. Water temperature had a statistically significant effect on eDNA concentration, probably reflecting the relationship between water temperature and spawning. We created generalised additive mixed models to estimate spawning activity periods based on weekly eDNA data. The estimated periods of spawning activity for common carp, largemouth bass and bluegill sunfish were March to May, May to July, and May to August, respectively. The estimated spawning periods coincided with known fish ecology or the results of traditional methods. This method also has been applied to daily eDNA samples, showing the feasibility of high‐resolution estimation of spawning activity. For common carp and bluegill sunfish, we were able to estimate the spawning period using this method. Although the method is affected by biomass and the diffusion and degradation of eDNA, it has the potential to accurately estimating spawning activities. These then can be estimated without conducting laborious traditional surveys, facilitating the monitoring of reproduction by rare, invasive or important fishery species. Further research on the diffusion distance and degradation time of the eDNA concentration peak caused by fish spawning activity may improve the accuracy of monitoring.
Japan’s long-term strategy submitted to the United Nations Framework Convention on Climate Change emphasizes the importance of improving the electrification rates to reducing GHG emissions. Using the five models participating in Energy Modeling Forum 35 Japan Model Intercomparison project (JMIP), we focused on the demand-side decarbonization and analyzed the final energy composition required to achieve 80% reductions in GHGs by 2050 in Japan. The model results show that the electricity share in final energy use (electrification rate) needs to reach 37–66% in 2050 (26% in 2010) to achieve the emissions reduction of 80%. The electrification rate increases mainly due to switching from fossil fuel end-use technologies (i.e. oil water heater, oil stove and combustion-engine vehicles) to electricity end-use technologies (i.e. heat pump water heater and electric vehicles). The electricity consumption in 2050 other than AIM/Hub ranged between 840 and 1260 TWh (AIM/Hub: 1950TWh), which is comparable to the level seen in the last 10 years (950–1035 TWh). The pace at which electrification rate must be increased is a challenge. The model results suggest to increase the electrification pace to 0.46–1.58%/yr from 2030 to 2050. Neither the past electrification pace (0.30%/year from 1990 to 2010) nor the outlook of the Ministry of Economy, Trade and Industry (0.15%/year from 2010 to 2030) is enough to reach the suggested electrification rates in 2050. Therefore, more concrete measures to accelerate dissemination of electricity end-use technologies across all sectors need to be established.
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