Japan Sea Coast Research Articles

Life‐history monographs of Japanese plants. 10: Fritillaria koidzumiana Ohwi (Liliaceae)

AbstractThe life‐history characteristics of Fritillaria koidzumiana Ohwi (Liliaceae) are described here. This is a typical spring ephemeral of deciduous forests in the lowlands of central Honshu, ranging from Yamagata to Ishikawa Prefecture along the Japan Sea coast, but with very peculiar disjunctions in Shizuoka and Yamanashi Prefectures on the Pacific side. This small insect‐pollinated polycarpic perennial herb bears a single unshowy greenish yellow flower, blooming downward, but attracting pollinators, such as small bees and flies, and produces numerous propagules exclusively by means of sexual reproduction. Frutescence occurs in late April to mid‐May. Seed outputs are high, with fecundity levels attaining approximately 75% per ovary. Seeds are furnished with an elaiosome and susceptible to ant dispersal.

Storm Waves on Japan Sea Coast on February 24, 2008 Observed by NOWPHAS Network

Storm Waves on Japan Sea Coast on February 24, 2008 Observed by NOWPHAS Network

The 2007 Noto Peninsula, Japan, Earthquake (Mw 6.7): Damage to Wooden Structures

The 2007 Noto Peninsula earthquake ( Mw 6.7, M jma 6.9) produced strong shaking throughout central Japan with substantial damage to more than 14,500 buildings. The shallow event occurred close to the Japan Sea coast (37.22°N, 136.69°E, depth 11 km) on 25 March 2007 at 00:41:58 GMT. Analyses of seismic data showed that it was a thrust fault (striking northeast and dipping downward to the southeast) with dimensions of about 15 × 30 km2 (figure 1; Aoi and Sekiguchi 2007). There was no significant surface faulting from the earthquake but Global Positioning System measurements showed surface displacements of 20 to 25 cm (Geographical Survey Institute 2007). The recent seismicity of the Noto Peninsula region has been relatively low and has included moderate events in 1933 ( Mjma 6.0) and 1993 ( M jma 6.6). For the latest earthquake, there were significant strong ground motions throughout the Noto Peninsula (figure 1), with maximum recorded ground velocities of 80 to 100 cm/s. Although the region is a relatively sparsely populated area of Japan, there was considerable damage to wooden structures, the predominant type of construction. There were 630 totally and 13,920 partially collapsed buildings, with damage concentrated in the towns of Monzen and Anamizu and lesser damage in downtown Wajima (Cabinet Office, Government of Japan 2007a). The cost of the total damage is estimated to be ¥65 billion (about U.S. $535 million) (Cabinet Office, Government of Japan 2007b). Despite the large number of severely damaged houses, there was only one fatality (not related to a building collapse) and 336 injured. As has been the case with other recent earthquakes in Japan, several groups quickly carried out detailed surveys of building damage. This paper presents some statistical results about damage to wooden structures from the Noto Peninsula earthquake, which characterizes the fragility …

Living on Past Glories and Future Dreams The Effects of Depopulation on Early Modern Urban Development in the Former Castle Town of Kanazawa

AbstractDepopulation of urban areas is a serious issue in twenty-first century Japan, as shown by the recent large-scale amalgamation of municipalities and programmes to combat declining central city areas. However, this is not the first time depopulation has had a significant effect on urban development: the decline in castle towns after the Meiji Restoration of 1868 had profound effects on both urban form and development concepts. Kanazawa, once one of the largest cities in Japan, suffered from an initial and long-lasting drop and then a more insidious decline as its Japan Sea coast location cut it off from the bulk of industrial and trade development. This article uses a two-fold approach to examine depopulation: first, an examination of the physical effects of depopulation based on statistical analysis of pre-war land registers shows the patterns of decline and regrowth throughout the modern period. Second, the impact of depopulation on the city's image of itself is examined through period documents such as council records and local newspapers. The need to regain status through population rank became an overarching goal of the urban leaders, and formed the basis of Kanazawa's reactions to the modern era and eventually towards imperialism.

Development and distribution of Castanea and Aesculus culture during the Jomon Period in Japan

Castanea and Aesculus trees were protected for consumption of nuts as food during the Jomon Period. Climatic factors affected the selection of kinds of consumed nuts. Castanea was mainly consumed during warm periods and Aesculus was consumed during cold periods. However, this could have been a regional phenomenon in northern Japan. It is possible that in southern warmer areas Castanea either might be protected constantly, or the protection of these plants was not necessary because forest productivity in the southern area is greater than that of the northern area. To understand the influence of temperature on Castanea hansaibai, pollen analysis was conducted at the Satohama site. In addition, the distribution of the intermediate stage between wild and domestication ( hansaibai) during the Jomon Period was studied based on pollen analyses. At the Satohama site, protection of Castanea started during the warm period in the Early Jomon Period (7000–4500 years BP) and continued to be observed during the next cold period. The Tohoku region (the northern part of Honshu Island) and the Hokuriku region (Japan Sea Coast area in Central Japan) was the main distribution area. In this study, no evidence of the protection of either species in Western Japan was detected. Climate and the necessity for large amounts of food preservation for winter might influence this activity.

Determination of 240Pu/ 239Pu atom ratio in coastal surface seawaters from the western North Pacific Ocean and Japan Sea

Surface seawater samples were collected from a site in the vicinity of the nuclear fuel reprocessing facility at Rokkasho, Japan and sites along the Japan Sea coast. 239+240Pu activities and 240Pu/ 239Pu atom ratios were determined by α-spectrometry and isotope-dilution sector-field ICP-MS. The 240Pu/ 239Pu atom ratio with the mean value of 0.227±0.006 was significantly higher than the mean global fallout ratio of 0.18. The contribution of the Pacific Proving Grounds close-in fallout was estimated to be 33% of the 239+240Pu.

Tomographic Imaging outside a Seismic Network: Application to the Northeast Japan Arc

The conventional local tomography can determine the 3D seismic velocity structure right beneath a seismic network, but it cannot determine the 3D structure outside a seismic network. In this study we show that such a limitation of tomography can be overcome if many earthquakes occur outside a seismic network. In the northeast Japan arc earthquakes occur actively from the Japan Trench to the Pacific coast. We detected and used sP -depth phase to relocate the suboceanic earthquakes accurately, and then used P - and S -wave arrival times from the relocated suboceanic events and the earthquakes under the northeast Japan land area to determine the 3D P - and S -wave velocity and Poisson’s ratio structures of the entire northeast Japan arc from the Japan Trench to the Japan Sea coast. Our results exhibit strong lateral heterogeneities under the forearc region. The mainshock hypocenters of large interplate earthquakes ( M 7.0–8.2) mainly cluster near the boundaries of high and low velocity and Poisson’s ratio above the subducting Pacific slab. A few large earthquakes are located in areas with high velocity and low Poisson’s ratio. These results suggest that lateral heterogeneities on the slab boundary can affect the rupture nucleation of large thrust earthquakes and the degree of interplate seismic coupling.

Genetic structure changes of expanding sika deer (Cervus nippon) populations in central and western Hokkaido, revealed by mitochondrial DNA analysis

Recent overpopulation of the sika deer (Cervus nippon) in Hokkaido has resulted in expansion of their distribution from eastern to western parts of this island. To assess changes of genetic population structures of the Hokkaido sika deer, mitochondrial DNA control sequences (602 base-pairs) from 283 animals collected from central and western Hokkaido were analyzed. Based on transitional substitutions (A < – > G) at four nucleotide sites, five haplotypes were identified. One haplotype was newly found in the present study, and the other four haplotypes referred to those reported previously. The distribution patterns of haplotypes showed characteristic changes of genetic population structures, compared with the past distribution of haplotypes. In northern Hokkaido, for instance, the population around the Okhotsk Sea-coastal region has clearly expanded to the Japan Seacoastal region. The population around the Ishikari-lowlands and the Hidaka mountains has increased within these areas, and it is not likely that the increase is directly caused by the immigration from eastern Hokkaido.

Doppler Radar Observation of a Tornado Generated Over the Japan Sea Coast during a Cold Air Outbreak

On January 18, 2001, a tornado formed over the Japan Sea near the Mikuni Town on the Hokuriku Coast of Japan. The “Mikuni Tornado” formed within a winter thundercloud, during a period of a cold air-outbreak, and heavy snowfall. The detailed structure of the tornado funnel cloud, and misocyclone with in the cloud are revealed from photographs, videotape, Doppler radar data, and the GPS sonde data. The tornado was generated 3 km offshore, close to the radar site. The tornado formed at the edge of a developing cell, had a single funnel, and was accompanied by a misocyclone near the cloud base; the position of the misocyclone corresponded well with a funnel cloud. The misocyclone had a diameter of 400-800 m and vorticity of 10−1 s−1, and coincided with the tornado funnel vortex in the cloud base. The funnel cloud had diameters of 150 m at the cloud base and 30 m near the surface, and a vorticity of 100 s−1. Although the funnel diameter at the cloud base changed remarkably during the life cycle of the tornado, the diameter near the surface remained largely unchanged. The funnel cloud began to dissipate after landing. The maximum wind speed of the tornado vortex is estimated to have been approximately 30 ms−1 (F0-scale), and the lifetime of the funnel cloud was 7 minutes. No damage or strong winds were recorded at the coastal radar site, which was located about 1 km from the tornado. The environmental feature that generated the Mikuni Tornado was vertical wind shear of the sub-cloud layer (3.5 × 10−2 s−1). The tornado was a non-supercell type tornado that formed under the uniform winter monsoon. This result indicates that small-scale snowclouds can produce tornadoes during periods of cold air outbreaks.

Estimating contribution of precipitation scavenging of atmospheric particulate mercury to mercury wet deposition in Japan

Mercury wet deposition is dependent on both the scavenging of divalent reactive gaseous mercury (RGM) and atmospheric particulate mercury (Hg(p)) by precipitation. Estimating the contribution of precipitation scavenging of RGM and Hg(p) is important for better understanding the causes of the regional and seasonal variations in mercury wet deposition. In this study, the contribution of Hg(p) scavenging was estimated on the basis of the scavenging ratios of other trace elements (i.e., Cd, Cu, Mn, Ni, Pb and V) existing entirely in particulate form. Their wet deposition fluxes and concentrations in air, which were measured concurrently from April 2004 to March 2005 at 10 sites in Japan, were used in this estimation. The monthly wet deposition flux of mercury at each site correlated with the amount of monthly precipitation, whereas the Hg(p) concentrations in air tended to decrease during summer. There was a significant correlation ( P<0.001) among the calculated monthly average scavenging ratios of trace elements, and the values in each month at each site were similar. Therefore, it is assumed the monthly scavenging ratio of Hg(p) is equivalent to the mean value of other trace elements. Using this scavenging ratio ( W), the wet deposition flux ( F) due to Hg(p) scavenging in each month was calculated by F= WKP, where K and P are the Hg(p) concentration and amount of precipitation, respectively. Relatively large fluxes due to Hg(p) scavenging were observed at a highly industrial site and at sites on the Japan Sea coast, which are strongly affected by the local sources and the long-range transport from the Asian continent, respectively. However, on average, at the 10 sites, the contribution of Hg(p) scavenging to the annual mercury deposition flux was 26%, suggesting that mercury wet deposition in Japan is dominated by RGM scavenging. This RGM should originate mainly from the in situ oxidation of Hg 0 in the atmosphere.

Secular crustal deformation and interplate coupling of the Japanese Islands as deduced from continuous GPS array, 1996–2001

Data from the nation-wide GPS continuous tracking network that has been operated by the Geographical Survey Institute of Japan since April 1996 were used to study crustal deformation in the Japanese Islands. We first extracted site coordinate from daily SINEX files for the period from April 1, 1996 to February 24, 2001. Since raw time series of station coordinates include coseismic and postseismic displacements as well as seasonal variation, we model each time series as a combination of linear and trigonometric functions and jumps for episodic events. Estimated velocities were converted into a kinematic reference frame [Heki, K., 1996. Horizontal and vertical crustal movements from three-dimensional very long baseline interferometry kinematic reference frame: implication for reversal timescale revision. J. Geophys. Res., 101: 3187–3198.] to discuss the crustal deformation relative to the stable interior of the Eurasian plate. A Least-Squares Prediction technique has been used to segregate the signal and noise in horizontal as well as vertical velocities. Estimated horizontal signals (horizontal displacement rates) were then differentiated in space to calculate principal components of strain. Dilatations, maximum shear strains, and principal axes of strain clearly portray tectonic environments of the Japanese Islands. On the other hand, the interseismic vertical deformation field of the Japanese islands is derived for the same GPS data interval. The GPS vertical velocities are combined with 31 year tide gage records to estimate absolute vertical velocity. The results of vertical deformation show that (1) the existence of clear uplift of about 6 mm/yr in Shikoku and Kii Peninsula, whereas pattern of subsidence is observed in the coast of Kyushu district. This might reflect strong coupling between the Philippine Sea plate and overriding plate at the Nankai Trough and weak coupling off Kyushu, (2) no clear vertical deformation pattern exists along the Pacific coast of northeastern Japan. This might be due to the long distance between the plate boundary (Japan trench) and overriding plate where GPS sites are located, (3) significant uplift is observed in the southwestern part of Hokkaido and in northeastern Tohoku along the Japan Sea coast. This is possibly due to the viscoelastic rebound of the 1983 Japan Sea ( M w 7.7) and the 1993 Hokkaido–Nansei–Oki ( M w 7.8) earthquakes and/or associated with distributed compression of incipient subduction there. We then estimate the elastic deformation of the Japanese Islands caused by interseismic loading of the Pacific and Philippine Sea subduction plates. The elastic models account for most of the observed horizontal velocity field if the subduction movement of the Philippine Sea Plate is 100% locked and if that of the Pacific Plate is 70% locked. However, the best fit for vertical velocity ranges from 80% to 100% coupling factor in southwestern Japan and only 50% in northeastern Japan. Since horizontal data does not permit the separation of rigid plate motion and interplate coupling because horizontal velocities include both contributions, we used the vertical velocities to discriminate between them. So, we can say there is strong interplate coupling (80%–100%) over the Nankaido subduction zone, whereas it is about 50% only over the Kurile–Japan trench.

Interplate coupling beneath NE Japan inferred from three‐dimensional displacement field

The northeastern Japan arc is located in a typical subduction zone and is a seismically active region where large interplate earthquakes have occurred repeatedly. The nationwide GPS network has made it possible to investigate the crustal deformation in unprecedented detail; however, vertical displacements are less accurate than the horizontal ones and have not been used to constrain interplate coupling models. In this study, GPS carrier phase data are analyzed in order to estimate three components of site displacements. The result indicates uplift along the Japan Sea coast and subsidence along the Pacific Ocean coast. Using the vertical site velocities together with the horizontal ones as the data for a geodetic inversion method, a new model of interplate coupling is constructed to explain both the horizontal and vertical velocities for the interseismic period from 1997 to 2001. The model demonstrates strong coupling in the area off Miyagi and in the area off Aomori through the area off Tokachi, including the areas of asperities. The downdip limit of the locked fault zone on the plate boundary has been estimated seismologically to be at a depth of 50–60 km in northeastern Japan, and the distribution of slip deficits derived in this study indicates that the transition zone extends down to a depth of about 100 km.

富山県八尾地域に分布する下部‐中部中新統の古地磁気学的研究

Machiko Tamaki, Yasuto Itoh and Mahito Watanabe (2006) Paleomagnetism of the Lower to Middle Miocene Series in the Yatsuo area, eastern part of southwest Japan: clockwise rotation and marine transgression during a short period. Bull. Geol. Surv. Japan, vol. 57 (3/4), 73-88, 8 figs, 1 table. Abstract: Process of the tectonic rotation related to Japan Sea opening is viewed from tilt-corrected paleomagnetic data obtained from the Early to Middle Miocene sequence in the Yatsuo area on the Japan Sea coast, eastern part of southwest Japan. Progressive demagnetization experiments have been executed on samples obtained from two routes along the Yamada and Wada Rivers, and success- fully isolated stable primary magnetic components in 16 sites. Together with data of previous studies, tilt-corrected reliable paleomagnetic directions comprising 10 normal and 27 reversed polarity sites of the Yatsuo Group on accurate stratigraphic positions show systematic temporal variation of east- erly deflection in declinations. On the basis of our presented magnetostratigraphy, Yatsuo Group is assigned from the late Early to early Middle Miocene. Significant stage of rotation as much as 30° is specified during late Early Miocene between a period of active volcanism and subsequent period of marine transgression. We suggest that the Japan Sea opening event had a final phase of rapid rotation around the late Early Miocene, which seems to have caused marine transgression in relation to re- markable subsidence along the Japan Sea coast.

Ethnogenesis and craniofacial change in Japan from the perspective of nonmetric traits

To examine population affinities in light of the ‘dual structure model’, frequencies of 21 nonmetric cranial traits were analyzed in 17 prehistoric to recent samples from Japan and five from continental northeast Asia. Eight bivariate plots, each representing a different bone or region of the skull, as well as cluster analysis of 21-trait mean measures of divergence using multidimensional scaling and additive tree techniques, revealed good discrimination between the Jomon-Ainu indigenous lineage and that of the immigrants who arrived from continental Asia after 300 BC. In Hokkaido, in agreement with historical records, Ainu villages of Hidaka province were least, and those close to the Japan Sea coast were most, hybridized with Wajin. In the central islands, clines were identified among Wajin skeletal samples whereby those from Kyushu most resembled continental northeast Asians, while those from the northernmost prefectures of Tohoku apparently retained the strongest indigenous heritage. In the more southerly prefectures of Tohoku, stronger traces of Jomon ancestry prevailed in the cohort born during the latest Edo period than in the one born after 1870. Thus, it seems that increased inter-regional mobility and gene flow following the Meiji Restoration initiated the most recent episode in the long process of demic diffusion that has helped to shape craniofacial change in Japan.

Descriptions of phyllosoma larvae of Scyllarus bicuspidatus and S. cultrifer (Decapoda, Scyllaridae) collected in Japanese waters

For understanding larval recruitment processes of Scyllarus and Panulirus lobsters, exact species identifi- cation of field-caught phyllosoma larvae, particularly those of the early stages, is essential. Using ichthyoplankton sam- ples from waters along the west coast of Kyushu to the Japan Sea coast of Honshu and the Kuroshio and Kuroshio- Counter Current regions, we described morphological features of the I to VIII (final) stage phyllosoma larvae of S. bi- cuspidatus and the IV to VIII stage larvae of S. cultrifer. The larvae of equivalent stages of two Scyllarus species are distinguishable from each other by using the combinations of body lengths and morphological features of antennules, pereiopods and pleopods. In addition, a) equivalent larval stages in S. cultifer are always larger than in S. bicuspidatus; b) cephalic shield of S. bicuspidatus is rounder than in S. cultrifer; c) relative to antennule length, the eyestalk is longer in S. cultrifer than in S. bicuspidatus.

Regional variations in wet and dry deposition fluxes of trace elements in Japan

The annual wet and dry deposition fluxes of 12 trace elements (i.e., As, Cd, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se and V) were measured on the basis of 1 year of observations (December 2003–November 2004) at 10 sites in Japan. Precipitation and dry deposition (gases and particles) samples were collected every half month using an automatic sampler, which is composed of a precipitation sampler and a water surface sampler for dry deposition. The wet deposition fluxes of Hg, Pb and Se exceeded their dry deposition fluxes at most sites. In contrast, the dry deposition fluxes of Cr, Cu, Mn, Mo, Ni and V were significantly higher than their wet deposition fluxes. The annual wet deposition fluxes of trace elements except for Cu, Mo and Ni were correlated with the annual precipitation amount ( P < 0.05 ). In particular, about 70–80% of the variance of the wet deposition fluxes for Hg ( r 2 = 0.80 ), Sb ( r 2 = 0.68 ) and V ( r 2 = 0.80 ) was explained using the precipitation amount. The wet deposition fluxes of As, Cd, Pb and Se at sites on the Japan Sea coast tended to be higher than those expected from the precipitation amount. This suggests a large contribution of their long-range transport from the Asian continent. On the other hand, the regional variations in the dry deposition fluxes of the trace elements were different from those in the wet deposition fluxes. A markedly higher dry deposition fluxes were observed at sites in industrial and urban areas. The relatively high dry deposition fluxes of Cr, Cu, Mn, Ni and Pb suggest that these elements are mainly from electric steel furnaces near the sites, because they are abundant in furnace emission particles. The results of lead isotope analyses indicate that the lead isotope ratios in the dry deposition samples at industrial and urban sites are different from those at other sites. This implies that lead dry deposition at such sites is dominated by emissions from peculiar sources, although whether those sources are the electric steel furnaces is unknown.

Vertical distributions of particles and sulfur gases (volatile sulfur compounds and SO 2) over East Asia: Comparison with two aircraft-borne measurements under the Asian continental outflow in spring and winter

We have presented the vertical distributions, between 0.5 and 5.5 km, of particles, volatile sulfur compounds, sulfur dioxide, O 3, and fractions of sulfur over the Japan Sea coast, Wakasa Bay, on 23 April 1996 and 28 December 1995. Comparison of these measurements showed that free tropospheric concentrations of particles and short-lived sulfur gases (CS 2, H 2S, SO 2) on 23 April 1996 were significantly higher than those on 28 December 1995. Clustered isentropic backward trajectory analysis and meteorological data indicated that the difference was associated with air mass transport routes and meteorological conditions. On 23 April 1996, coarse size particles (mineral dust particles) were injected over the arid region associated with dust storms. During transport by westerly winds, these coarse size particles were mixed with short-lived sulfur gases injected by convection over an industrial region. The presence of DMS, confined to the boundary layer, indicated that Asian continental outflow can be modified during long-range transport through mixing with marine air in the boundary layer over the Japan Sea. On the other hand, on 28 December 1995, low concentrations of particles and short-lived sulfur gases, measured at altitudes above 3.0 km, were due to air mass subsidence. It is likely that some photochemical processing was also due to low concentrations of short-lived sulfur gases. Vertical distributions of O 3 concentrations and values of sulfur fraction (SO 4 2−/(SO 4 2−+SO 2)) supported this interpretation. There was no significant difference in concentrations of long-lived COS, except for one sample on 23 April 1996. The low COS concentration coincided with significantly high concentrations of CS 2, suggesting rapid upward transport of COS depleted air masses from the surface.

Eustatic sea-level change at the Mid-Pleistocene climate transition: new evidence from the shallow-marine sediment record of Japan

Abstract Based on the excellent sedimentary record, we have identified five depositional sequences in the upper part of the Omma Formation, exposed along the Japan Sea coast of central Japan. The base of this stratigraphic section is placed just below the top of the Jaramillo Subchron, and the top is located below the Brunhes-Matuyama boundary. Biostratigraphy supports the interpretation that the lower three sequences correlate with marine oxygen isotope stages (MIS) 28–26, 26–24 and 24–22, respectively. We have reconstructed a eustatic sea-level curve from analyses of sedimentary facies, fossil molluscs, basin subsidence and sediment accumulation. The resulting sea-level curve shows that mean eustatic sea-level dropped between 1.0 and 0.9 Ma, and that sea-level was lowest at MIS 22, which has the heaviest δ 18O value between MIS 28 and 22. The total fall in mean sea-level is inferred to be 20–30 m. This independent sea-level record demonstrates that ice-sheet volume rapidly increased at the Mid-Pleistocene Climate Transition (MPT) and culminated in MIS 22, as inferred from the δ 18O record. The upper two depositional sequences imply the contribution of precession to changes in ice sheet volume would have arisen in MIS 21, just after the MPT.

High-resolution maps of Coda Q in Japan and their interpretation by the brittle-ductile interaction hypothesis

Abstract Using seismograms recorded at 582 Hi-net stations for earthquakes located within 30 km from each station, we measured coda Q for frequency bands of 1–2, 2–4, 4–8, 8–16, and 16–32 Hz, respectively. Then coda Q maps are constructed with average station spacing of 20 km over Japan, except the Hokkaido Island. The most striking feature of the obtained maps is the significant spatial variation within Japan, up to a factor of 3 for the lower frequency bands, as well as its strong frequency dependence. Such high spatial resolution was not possible to achieve without the high density and sensitivity of the Hi-net. We found several low coda Q regions for frequency band of 1–2 Hz including the southwestern Shikoku, eastern Shimane-western Tottori along the Japan Sea coast and the disjointed spots along the Pacific coast from the Kanto-Tokai region to southern edge of the Kii-peninsula. However, the most conspicuous low coda Q zone is a narrow belt from Niigata towards south-west to the Biwa lake along the Japan Sea coast. This low Q zone appears at frequency bands of both 1–2 and 2–4 Hz, and it coincides with the zone of high deformation rate revealed from the GPS data. For frequency bands 4–16 Hz (2–4 Hz in Kyushu), the low coda Q areas agree with volcanic and geothermal areas. For frequency band of 16–32 Hz, the coda Q is distributed nearly uniformly throughout the study area.

Genetic Differentiation of the Gobies Gymnogobius castaneus and G. taranetzi in the Region Surrounding the Sea of Japan as Inferred from a Mitochondrial Gene Genealogy

The phylogenetic relationships between gobies of the genus Gymnogobius were analyzed using mitochondrial cytochrome b gene sequences, focusing on the species currently classified as G. taranetzi and G. castaneus that occur in Japan, South Korea, and Russia. Gobies of the two species collected at 12 localities in Japan, South Korea, and Russia formed a monophyletic clade (called the "castaneus species complex" here) with G. breunigii as the sister clade. Within the species complex, six lineages were recognized: (L1) G. castaneus from the Akigawa River, Tokyo, Japan; (L2) G. castaneus from Yuza, Yamagata, Japan; (L3) G. taranetzi from Russia and South Korea; (L4) G. castaneus from the Tonegawa River, Chiba, Japan; (L5a) G. taranetzi from Shimane, Japan; and (L5b) G. castaneus + G. taranetzi from the Japan Sea coast of northern Japan. The two local lineages of G. castaneus (L1 and L2) are highly divergent from the others. The Japanese populations of G. taranetzi have diverged from the continental G. taranetzi populations, while one mitochondrial lineage (L5b) is shared with G. castaneus of northeast Japan. Therefore, the current species G. taranetzi and G. castaneus as defined morphologically are polyphyletic, necessitating a taxonomic revision. The genetic differentiation of isolated local lineages and the evolution of taranetzi-and castaneus-type gobies have likely occurred repeatedly in brackish/freshwater habitats around the Sea of Japan. We discussed the time of divergence for these gobies based on a tree with the molecular clock assumption.