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Redd superimposition, spawning on a previous spawner's redd by a later spawner, reduces reproductive success of the previous spawner. Therefore, in streams where redd superimposition frequently occurs, late-spawning species have a competitive advantage over early-spawning species. We hypothesised that smaller channels of upper reaches would have higher potential of redd superimposition owing to lower availability of spawning habitat, thereby providing a competitive advantage to latespawning species, to explain a displacement of native masu salmon (Oncorhynchus masou ishikawae) by non-native white- spotted char (Salvelinus leucomaenis) (late spawner) specific to small upper reaches in a Japanese river. We examined (1) the availability of spawning habitat and (2) overlap in spawning habitat characteristics between the two species in streams with different channel size. The results showed that (1) the habitat availability decreased upstream as channel size decreased, and (2) characteristics of spawning habitat highly overlapped between the two species in small channels, whereas those differed significantly between the two species in larger channels, supporting our hypothesis. Our results provide a new perspective on longitudinal changes in competitive advantages in salmonids. Key words: interspecific competition, longitudinal replacement, redd superimposition, spawning habitat, stream size, Introduction Redd superimposition, spawning on a previous spawner's redd by a later spawner, has been recognised as a form of intraspecific and interspecific competition in salmonids (Hayes 1987; Essington et [...]

Background: It has been suggested that a short nap in the afternoon may improve sleepiness, alertness, and task performance. The present study evaluated the effects of a 30-min rest with a new nap chair on task performance, sleepiness, and neurophysiological measures. Methods: A randomized controlled crossover trial with a 1-week interval was carried out at the BOOCS Clinic Fukuoka in Japan. The subjects were male workers aged 20 to 64 years with suspected brain fatigue, which was defined by the Profile of Mood Status 2. The intervention was a 30-min rest with an office chair or a nap chair. The primary outcome was the performance in the Uchida-Kraepelin test. The secondary outcomes included the Karolinska Sleepiness Scale and 15-min heart rate variability (HRV). The changes after the nap-chair rest and office-chair rest were compared. Repeated measures analysis of variance with nesting was used in the statistical analysis. Results: Twenty participants were eligible and entered the crossover trial. The overall 15-min score in the Uchida-Kraepelin test improved after the nap-chair rest and after the office-chair rest to almost the same extent (5.9 vs. 5.5 points, P = 0.68). The Karolinska Sleepiness score significantly decreased after the nap-chair rest, and the between-treatment difference in the decrease was highly significant (P = 0.0004). The average duration of sleep during rest was prominently longer in the nap-chair rest than in the office-chair rest (19.0 vs. 7.6 min, P = 0.002). No participants experienced REM sleep during the rest. LF and HF powers of the HRV were greater during the nap-chair rest than during the office-chair rest, the difference in the HF power being substantial. Conclusion: A 30-min rest with the nap chair did not appreciably improve the performance in the Uchida-Kraepelin test as compared with the office-chair rest. The nap-chair rest induced a substantially longer sleep accompanied with a parasympathetic activation, thereby resulting in a material improvement in sleepiness after the rest. [ABSTRACT FROM AUTHOR]

Regional and local habitat factors affecting the distribution and abundance of Japanese eel (Anguilla japonica) were systematically analysed in 123 reaches of 21 stream systems in south‐western Japan, with particular attention paid to human habitat modification, such as artificial barriers and concrete revetment.The density of Japanese eel decreased upstream, and they were absent from the upper reaches of each stream system. The upper limits of their distribution were explained by the distance from the sea and the channel gradient, rather than barriers. However, the number of barriers had the highest explanatory capacity for the upstream decline in abundance of small eels (<40 cm in total length).Analyses of the relative importance of regional and local habitat factors showed that the number of barriers (regional factor) was more important than local habitat factors in determining small eel abundance, whereas regional and local habitat factors (e.g. concrete revetment or cover habitat) were similarly important for large eel abundance.These results suggest that: (i) barriers are not a major factor limiting the distribution (presence/absence) of the Japanese eel in the streams studied; (ii) barriers can substantially decrease the abundance of young eels; and (iii) as eels grow older and larger, local habitat factors, such as bank conditions and cover, become more important in determining their abundance.The results for the relative importance of regional and local habitat factors suggest that in habitat restoration for the Japanese eel, priority should be given to mitigating barrier effects. The improvement of longitudinal connectivity to facilitate colonization by young eels is primarily needed for a more efficient use of the existing carrying capacity of streams. The improvement of local habitat conditions to increase the carrying capacity should be conducted in stream reaches free from barrier effects. [ABSTRACT FROM AUTHOR]

Factors controlling invasion success of rainbow trout (Oncorhynchus mykiss) and interactions with native masu salmon (Oncorhynchus masou) were examined by field investigations. The results suggested that flow regime has a major role in controlling rainbow trout invasion success. Although competitive relationships were found between the two species, masu salmon were not likely to prevent trout invasion. Analyses on the distributions and abundances of the two species indicated that the occurrence of rainbow trout was limited to streams with stable flows, and the density of each species was negatively related with that of the other. Habitat use and diet analyses revealed a pattern of their resource partitioning; rainbow trout occupy positions near the bottom or cover, foraging benthic prey, while masu salmon feed drifting prey at the middle layers of the water column. This resource partitioning was suggested to reflect a diet shift by rainbow trout. Our results also have a management implication that dams, which control flow regime, can be a key factor in managing rainbow trout invasion and its effects. Des observations de terrain ont permis d'examiner les facteurs qui controlent le succes de l'invasion de la truite arc-en-ciel (Oncorhynchus mykiss) et ses interactions avec le saumon masou (Oncorhynchus masou) indigene. Les resultants font croire que le regime d'ecoulement des eaux a un role majeur dans le controle du succes de l'invasion des truites. Bien qu'il existe des relations de competition entre les deux especes, il est peu probable que les saumons masou empechent l'invasion des truites. Des analyses de la repartition et de l'abondance des deux especes indiquent que la presence de la truite arc-en-ciel est restreinte aux cours d'eau a ecoulement stable; il y a aussi une relation negative entre les densites des deux especes. Des analyses de l'utilisation de l'habitat et du regime alimentaire montrent un patron de partage des ressources : les truites arc-en-ciel se tiennent pres du fond ou des abris et se nourrissent de proies benthiques, alors que les saumons masou s'alimentent de proies en derive dans les couches intermediaires de la colonne d'eau. Ce partage des ressources semble refleter un changement de regime alimentaire chez la truite arc-en-ciel. Nos resultats ont aussi des consequences sur la gestion, puisque les barrages, qui controlent le regime d'ecoulement, peuvent etre un facteur essentiel pour gerer l'invasion des truites arc-en-ciel et ses effets. [Traduit par la Redaction], Introduction Invasions by non-native species are a major threat to biodiversity and ecosystem health. Once non-native species establish self-reproducing populations, they can exert strong impacts on native communities at various [...]