日本北海道地区细石叶技术研究概述

细石叶技术是晚更新世晚期东北亚和西北美新的变革性剥坯技术和适应手段。北海道地区拥有丰富、多样的细石器遗存,相关材料最早可以追溯到距今约2.5万年前,持续了约1.2万年。以北海道具有明显技术复杂性和多样性特点的细石器为材料,学者们基于技术式"阅读"和拼合研究划分出一系列细石核工艺类型和剥坯技法;岛内以楔形细石核为代表的细石器工业传统在不断延续的同时,也表现出明显的阶段性变化,并在一定程度上显示出与气候环境变化较强的相关性。本文对北海道地区晚更新世末次盛冰期以来的气候、环境背景以及细石器的发现与研究历程进行介绍。在此基础上,厘清北海道细石核工艺类型的划分,并对细石器群的阶段性演变进行系统梳理,以期对我国相关研究有所裨益。     

Use of ELISA to monitor bacterial kidney disease in naturally spawning chinook salmon

Bacterial kidney disease (BKD) caused by Renibacterium salmoninarum (Rs) is a serious problem among Pacific Northwest salmon hatcheries and has raised concerns that salmon reared in hatcheries may spread BKD to natural populations. In order to monitor the potential spread of this disease to salmon spawning in nature, a method must be available to collect and analyze tissues from naturally spawning salmon. Kidney tissue analyzed by enzyme-linked immunosorbent assay (ELISA) is the standard method to detect the presence of Rs in salmon sampled in hatcheries. In this study, we tested the validity of using ELISA on kidney tissue collected from intact carcasses recovered on the spawning grounds to monitor BKD in naturally spawning populations by comparing ELISA optical density (OD) values from kidney tissue that was subjected to conditions that simulated decomposition in a carcass and collection during a spawning ground survey with samples freshly collected from salmon at a hatchery. Mean ELISA OD levels were 1.060 for the samples prepared by the normal preparation and 1.115 for samples prepared by simulating spawning ground survey collection. There was no significant difference in mean ELISA OD between the 2 sample preparations and the relationship did not significantly differ from 1:1 (slope = 0.946). This demonstrates that BKD prevalence in natural populations can be monitored using ELISA conducted on samples from intact carcasses recovered on spawning ground surveys. This will be an important tool for monitoring the effect of hatchery supplementation on naturally spawning salmon populations.     

Hierarchical genetic structure of native masu salmon populations in Hokkaido,Japan

Identification of the spatial extent of genetic structuring that may be influenced by evolutionary, ecological and historical factors is critical for effective conservation or management strategies. Masu salmon Oncorhynchus masou is commonly distributed in Far East, however, many local populations have been under threats of decline due to habitat destruction, overexploitation, and genetic introgression. To reveal the spatial genetic structure of native masu salmon populations in Hokkaido, masu salmon samples were collected from 16 rivers in which there was no official record of artificial releases of any masu salmon stock and were analyzed using 15 microsatellite loci. A Bayesian assignment test revealed that masu salmon populations were divided into two genetically distinct groups: the northeastern and southwestern groups. For within-group genetic structure, all populations, except for geographically proximate populations, were significantly different from each other. AMOVA revealed that genetic variation at among-group level based on groups identified assignment test was greater than that of groups based on geographic locations. There was no significant IBD for the 16 populations. However, the Mantel test revealed significant IBD for the northeastern group, but did not for the southwestern group. This study suggested that native masu salmon populations in Hokkaido exhibit a hierarchical genetic structure that is largely a result of their precise homing behavior. The results of this study also highlight the importance of defining populations by using genetic data rather than by using predefined populations based on geographic locations for the correct determination of genetic structure.     

Effects of salmon carcasses on experimental stream ecosystems in Hokkaido,Japan

The effects of salmon carcasses on dissolved nutrients, epilithic production, leaf decomposition rates, and aquatic invertebrates were examined using 10-m-long artificial channels fed by an adjacent natural stream in Hokkaido, northern Japan. Bags containing maple leaf litter were placed in nine channels, each of which was assigned to one of three treatments with three replicates, for 6 weeks in fall 2002. The three treatments were: (1) salmon carcasses+invertebrates, (2) invertebrates only, and (3) control (no salmon carcasses or invertebrates added). Nutrient concentrations, biomass of epilithic algae (chlorophyll), leaf weight loss, abundance and biomass of invertebrates in the leaf packs were compared among the three treatments at 14, 27, and 40 days after the beginning of the experiment. The NH₄⁺ in stream water and chlorophyll concentrations of epilithic algae were higher in the salmon treatment than the other treatments, and the maple leaves decomposed faster in the salmon treatment than in the other treatments. Moreover, the N content of the leaves was highest and the C/N ratio was lowest in the salmon treatment, although not significantly so. The abundance and biomass of the dominant leaf-shredding invertebrate Goerodes satoi did not differ between the first two treatments. However, the stable N isotope ratio in G. satoi was nearly 3 higher in the salmon treatment, suggesting that around 20% of salmon-derived N was taken up by this shredder. Our results indicate that salmon carcasses affect stream ecosystems directly by enhancing primary production, indirectly by accelerating woody leaf decomposition, and finally by incorporating into the food web primary consumers that utilize fertilized woody leaves.     

Long-term growth dynamics of natural forests in Hokkaido,northern Japan

Abstract. The long-term growth dynamics of natural forest stands on the island of Hokkaido were described on the basis of an analysis of data from 38 permanent plots spanning 15–22 yr. Stand structure was characterized by basal area, stem density and tree size variability. To detect trends in stand structure, regression models for recruitment rate (per ha per yr), mortality rate and the rate of change in stem density and tree size variability were developed by a stepwise method using initial basal area, stem density, tree size variability, species composition summarized by LNMDS ordination, altitude, annual mean temperature, annual precipitation, type of understorey vegetation, topography and slope aspect as candidates for predictor variables. The same analyses were conducted for basal area increment (net growth) and its components: survivor growth = basal area gain by growth of surviving individuals and mortality = basal area loss by death of individuals. Stem density remained generally unchanged; recruitment was relatively low even in very sparse stands. Stand basal area generally increased as survivor growth was approximately double the mortality. Recruitment rate was strongly affected by the presence of dwarf bamboo (Sasa spp.) vegetation on the forest floor which inhibited tree regeneration. Mortality rate was density-dependent; dense stands had higher mortality than sparse stands. Density change rate (recruitment rate - mortality rate) was, therefore, determined by both the type of understorey vegetation and stem density. Survivor growth was high in stands with high stem density and basal area. Mortality was dependent on basal area and altitude. Net basal area increment (net growth) was dependent only on stem density with other factors that influenced survivor growth and mortality omitted. Tree size variability decreased in stands with high tree size variability whereas it increased in stands with low size variability. Based on the obtained models for density change rate and net basal area increment, trajectories of stands were illustrated on a log-log diagram of stem density and basal area. The predicted differences in trajectories as affected by the understorey vegetation type indicated the importance of dwarf bamboo vegetation for forest dynamics on Hokkaido.     

The occurrence and run timing of naturally spawning chum salmon in northern Japan

Since the late 20th century, the biomass of Pacific salmon Oncorhynchus spp. has increased. Hokkaido, northern Japan, is one of the main areas of chum salmon O. keta production in the North Pacific and intensive hatchery programs support the recent high abundance. However, proper management of naturally spawning populations is necessary to conserve healthy stocks of this species. In 2008, we started a program to assess the naturally spawning chum salmon populations in Hokkaido. Of the total of approximately 1,500 rivers in Hokkaido, 238 rivers with lengths of longer than 8 km (excluding those rivers used for hatchery broodstock collection) were surveyed in 2008 and 2009. The number of non-enhanced rivers found to contain naturally reproducing chum salmon was 59 (31.4% of surveyed rivers) and 50 (37.6% of surveyed rivers) rivers in 2008 and 2009, respectively. Including the rivers where hatchery broodstock were collected and rivers shorter than 8 km that contain naturally spawning chum salmon, chum salmon ascended at least 191 and 175 rivers in Hokkaido in 2008 and 2009, respectively. Repeated foot surveys indicated that the run timings of naturally spawning chum salmon may be affected by coastal commercial fisheries. This study showed that naturally spawning chum salmon remain in many rivers in Hokkaido where hatchery programs have been intensively conducted.     

Response of microbial community structure to natural and accelerated hydrarch successions in the boreal wetlands in northern Hokkaido, Japan

We estimated the effect of invading Sasa vegetation and accelerated terrestrialization on the microbial community structure in Sarobetsu-genya wetland (SGW) and Nakanominedaira wetland (NW) (original vegetation, Sphagnum). All examined peat-pore water samples were acidic. Electrical conductivity significantly differed between SGW and NW. Nonmetric multidimensional scaling (NMDS) and analysis of similarity based on denaturing gradient gel electrophoresis (DGGE) band patterns revealed differences in the bacterial community structure between the Sasa and Sphagnum vegetations at a depth of 10 cm in NW. In contrast, the bacterial NMDS profiles at all depths differed between the 2 wetlands rather than between the 2 vegetations. The archaeal community structure significantly differed between the wetlands at depths of 30 and 50 cm. The bacterial diversity index derived from the DGGE profiles significantly differed between the wetlands at all depths. The archaeal diversity index significantly differed between the wetlands at a depth of 50 cm. Sasa invasion affected the microbial community structure in the rhizosphere, up to a depth of 10 cm; this effect differed with the terrestrialization speed. These results suggest that in peat bogs subjected to artificially accelerated terrestrialization, the microbial community changes before the occurrence of the natural hydrarch ecological succession involving ground vegetation.     

Influences of habitat fragmentation by damming on the genetic structure of masu salmon populations in Hokkaido, Japan

Dam construction dramatically influences riverine ecosystems, with habitat fragmentation being one of the most serious impacts. This habitat fragmentation is particularly relevant for anadromous species such as salmonids. We examined the effects of habitat fragmentation on masu salmon (Oncorhynchus masou) populations in Hokkaido, Japan. Specifically, we sampled from 15 locations located above and below a dam region in the Uryu River system, and analyzed the genetic structure of the populations using 10 microsatellite loci. No indication of a significant reduction in genetic diversity, estimated by allelic richness and heterozygosity, was observed within the above-dam region compared to the below-dam region. However, we also found that reducing the number of alleles had occurred within the above-dam region. The analysis of molecular variance and multidimensional scaling analysis indicated significant genetic differentiation between regions and within each region. A significant relationship between genetic and geographic distance was observed in the below-dam region, while no signal of isolation by distance was detected in the above-dam region. This study suggests a possibility of ongoing loss of alleles coinciding with habitat fragmentation caused by anthropogenic environmental changes such as water-level regulation, which negatively impacts genetic structure.     

Dispersal patterns of anadromous and freshwater resident masu salmon at different spatial scales in mid-western Hokkaido,Japan

To evaluate the influences of spatial scale on dispersal, the dispersal patterns of masu salmon Oncorhynchus masou masou were investigated at among-river (ca. <43 km) and within-river levels in mid-western Hokkaido, Japan. A genetic differentiation (F _ST) and assignment test showed that among-river dispersal was much less common (2.9 % of 339 individuals) than within-river dispersal (7.4 % of 190 individuals). We also found that there was no bias in dispersal at the among-river level, while anadromous males were more likely to disperse at the within-river level, suggesting that the dispersal patterns may be scale dependent.     

A GIS-based simulation program to predict multi-species size-structure dynamics for natural forests in Hokkaido, northern Japan

A simulation program that runs on a geographic information system (GIS) was developed to predict the multi-species size-structure dynamics of forest stands. Because important characteristics of a forest stand, including woody biomass accumulation, carbon storage, commercial value of timber, and functions for environmental conservation, can be inferred from the size structures of the component populations, management plans can be made from the predictions of the size-structure dynamics. For example, the simulation can incorporate various forms of thinning; forest managers can then try several thinning plans in simulated forest stands and choose the appropriate plan that achieves the best results. Using GIS to predict the size-structure dynamics of forest stands is of practical importance, because GIS has been used widely in forest management and can easily handle spatial distributions of environmental information (e.g., climate, geology, soils) that may influence tree performance. To predict size-structure dynamics, the program numerically solves a continuum equation that describes size-structure dynamics based on growth and mortality rates of individual trees. When predicting size-structure dynamics of a forest stand, the program obtains the environmental information of the stand from a database stored in the GIS and calculates environmental factors such as warmth index and potential evapotranspiration/precipitation ratio that influence growth and mortality rates. The simulation program calculates growth and mortality rates using published growth and mortality models that incorporate the effects of size of the individual, competition between trees, and abiotic environmental factors. To demonstrate the effects of abiotic environmental factors on the multi-species size-structure dynamics, sensitivity analyses were conducted. The size-structure dynamics varied in a way that was predictable from the responses of the growth and mortality rates to variations in the abiotic environmental factors. To demonstrate the size-structure dynamics in different locations, five test runs of the simulation program were also performed using the same initial size-structure and five different sets of abiotic environmental conditions from five locations. At the end of the simulation, the predicted size structures differed because the growth and mortality rates differed among the five locations. Finally, the response of the size structure to thinning was clarified. The result showed how the size structure of a component species in a forest stand is dependent on the presence of other species.     

Perspectives on wild and hatchery salmon interactions at sea,potential climate effects on Japanese chum salmon,and the need for sustainable salmon fishery management reform in Japan

Pacific salmon (Oncorhynchus spp.) play an important role as a keystone species and provider of ecosystem services in the North Pacific ecosystem. We review our studies on recent production trends, marine carrying capacity, climate effects and biological interactions between wild and hatchery origin populations of Pacific salmon in the open sea, with a particular focus on Japanese chum salmon (O. keta). Salmon catch data indicates that the abundance of Pacific salmon increased since the 1976/77 ocean regime shift. Chum and pink salmon (O. gorbuscha) maintained high abundances with a sharp increase in hatchery-released populations since the late 1980s. Since the 1990s, the biomass contribution of hatchery returns to the total catch amounts to 50% for chum salmon, more than 10% for pink salmon, and less than 10% for sockeye salmon (O. nerka). We show evidence of density-dependence of growth and survival at sea and how it might vary across spatial scales, and we provide some new information on foraging plasticity that may offer new insight into competitive interactions. The marine carrying capacity of these three species is synchronized with long-term patterns in climate change. At the present time, global warming has positively affected growth and survival of Hokkaido populations of chum salmon. In the future, however, global warming may decrease the marine carrying capacity and the area of suitable habitat for chum salmon in the North Pacific Ocean. We outline future challenges for salmon sustainable conservation management in Japan, and recommend fishery management reform to sustain the hatchery-supported salmon fishery while conserving natural spawning populations.     

Occurrence of actinosporean stages of myxosporeans in an inflow brook of a salmon hatchery in the Mena River System,Hokkaido, Japan

Actinospore infection of oligochaetes living in the mud and on the roots of vegetation in an inflow brook of a Hokkaido salmon hatchery was studied within the framework of a Japanese-Hungarian research program. Two triactinomyxon types, 1 echinactinomyxon, and 1 neoactinomyxum type were isolated from the oligochaete Rhyacodrilus komarovi Timm, 1990 collected during the survey. The aurantiactinomyxons were recorded over a period of 3 mo starting from the day after oligochaete collection. The oligochaetes released actinospores for several weeks from the first day of the study. Spore excretion of individual oligochaetes was not synchronous. Of the oligochaetes examined, 0.7, 7, 3 and 3%, were infected with the echinactinomyxon, neoactinomyxum and the 2 types of triactinomyxon spores, respectively. Actinospore infection was intense in the positive oligochaetes in all 4 types. Of the 4 actinospore types presented here, 3 are described for the first time.     

Spatial distribution of juvenile masu salmon (Oncorhynchus masou) with incongruent genotypic and phenotypic sex in Hokkaido, Japan

To clarify the spatial distribution of masu salmon Oncorhynchus masou with incongruent genotypic and phenotypic sex, we compared the phenotypic sex determined by gonad analysis with the genotypic sex identified by a male-specific genetic marker, Growth hormone pseudogene (GHp), in 584 individuals inhabiting 23 rivers in Hokkaido, Japan. We found that the genotypic sex is different from the phenotypic sex for 39 individuals in 10 rivers. Among them, 35 individuals (89.7?%) were GHp?+?females phenotypically. The opposite feature was noted in the remaining four individuals (10.3?%). This study also revealed that GHp?+?phenotypic females are distributed mainly in the Sea of Japan, whereas GHp- phenotypic male tend to appear in the Sea of Okhotsk. In addition, there was a significant negative correlation between the distance from the Bishabetsu River, where frequency of GHp?+?phenotypic females was the highest, and the frequency of those individuals in each river. These results suggest that the distribution of masu salmon with incongruent genotypic and phenotypic sex would be related to the movement of individuals among the populations and regions.     

Some consequences of Pacific salmon hatchery production in Kamchatka: changes in age structure and contributions to natural spawning populations

Aggregate hatchery production of Pacific salmon in the Kamchatka region of the Russian Federation is very low (< 0.5% of total harvest, with five hatcheries releasing approximately 41 M juvenile salmon annually), but contributions in certain rivers can be substantial. Enhancement programs in these rivers may strongly influence fitness and production of wild salmon. In this paper we document significant divergence in demographic traits in hatchery salmon populations in the Bolshaya River and we estimate the proportion of hatchery chum salmon in the total run in the Paratunka River to demonstrate the magnitude of enhancement in this system. We observed a reduction in the expression of life history types in hatchery populations (ranging from 1 to 9 types) compared to wild populations (17 types) of sockeye salmon in the Bolshaya River. We found similar trends in Chinook salmon in the same river system. This reduced life history diversity may make these fish less resilient to changes in habitat and climate. We estimate hatchery chum salmon currently contribute 17-45% to the natural spawning population in the Paratunka River. As hatchery fish increase in numbers at natural spawning sites, this hatchery production may affect wild salmon production. It is important to investigate the risk of introgression between hatchery and wild salmon that can lead to reduction in salmon fitness in Kamchatka rivers, as well as the potential of ecological interactions that can have consequences on status of wild salmon and overall salmon production in this region.     

Bimodal length frequency distribution in 0+aged masu salmon,Oncorhynchus masou,in a natural stream of southern Hokkaido

The frequency distribution of the fork length of 0⁺ aged masu salmon,Oncorhynchus masou, changed from unimodal to bimodal distribution in autumn of the years from 1982 to 1984 in the Mogusa River of southern Hokkaido, Japan. The bimodal distribution consists of two (upper and lower) modal groups. These two groups resulted from a difference in growth rate of 0⁺ aged individuals in autumn. Fish belonging to the upper modal group are assumed to be potential 1⁺ smolts. Whether 0⁺ aged parr transform into smolt or remain as parr in the following spring may be related to the growth rate of fish in the first autumn.     

Genetic structure of masu salmon (Oncorhynchus masou) populations in Hokkaido, northernmost Japan, inferred from mitochondrial DNA variation

Genetic structure of masu salmon Oncorhynchus masou populations in Hokkaido was examined by analysing mtDNA NADH dehydrogenase subunit 5 gene (561 bp) of 382 individuals collected from 12 rivers, in which there were no records of artificial release. Analysis of molecular variance showed that between groups level and between populations within-group level explained each c. 10% of genetic variance. In neighbour-joining tree, four populations located in southern Hokkaido were clustered into a single group; however, other populations did not form any clear clusters. Fu's F _S, Tajima's D and a mismatch distribution test indicated a sudden expansion of population in the entire population of Hokkaido and the northernmost population of Chiraibetsu, which was genetically close to the southern Hokkaido group. The Sea of Japan and southern rivers, including those of southern Hokkaido, seem to have served as refugia for masu salmon during glacial periods, and their dispersal and straying in interglacial periods affected the genetic structure of masu salmon populations in Hokkaido.     

Dependency of Japanese harbor seals (Phoca vitulina) on salmon set nets at Cape Erimo,Hokkaido, Japan

In this study, we observed the behavior of two age groups of harbor seal (Phoca vitulina richardii), i.e., yearlings, which often become bycaught and individuals 2 yr or older, during their stays at salmon set nets at Cape Erimo, Japan. From July to November 2011–2015, acoustic receivers that track tagging seals were attached to three set nets located near the haul‐out site. Our observations showed that the mean visit interval and the mean stay of seals at the set nets during fishing operations were significantly higher than before operations. A cluster analysis, where Cluster 1 consisted of seals that spent a long time at the set nets and Cluster 2 consisted of the other seals, showed that seals in Cluster 1 visited the set nets every day, while Cluster 2 seals visited once every 3–5 d. In addition, age 2 + seals in Cluster 1 stayed longer at regular time frames (at night), suggesting that individuals of this age group in Cluster 1 are highly dependent on the salmon set nets as foraging sites at night. It is especially clear that the set nets near the haul‐out site have influenced the foraging ecology of some seals.