Northern Japan Sea Research Articles

Otolith radiocarbon signatures provide distinct migration history of walleye pollock around Hokkaido, Japan in the North-Western Pacific.

Trace elements and stable isotope ratios in otoliths have been used as proxies for the migration history of teleosts; however, their application in oceanic fishes remains limited. This study reports the first use of radiocarbons in otoliths to evaluate the horizontal migration histories of an oceanic fish species, the walleye pollock Gadus chalcogrammus. We conducted radiocarbon analyses of three stocks sourced from Hokkaido, Japan. The radiocarbon concentrations from the outermost portion of the otoliths from the Japanese Pacific, Northern Japan Sea (JS), and Southern Okhotsk Sea (OS) stocks were in general agreement with the seawater radiocarbon concentration of the sampling region, suggesting that pollock of all three stocks generally inhabited the within the sea region where each pollocks were sampled throughout their life cycle. However, the radiocarbon signals also provided some indications that some JS and OS stocks may be migrating between different sea regions. The proposed novel approach of reconstructing the individual migration history of marine fish using radiocarbon in otoliths may help examine fish migration with a higher temporal and spatial resolution that could not be achieved by trace elements and stable isotope ratios.

North-south discrepancy in the contributors to CB153 accumulation in the deep water of the Sea of Japan

The deep-water environment and its ecosystem are becoming the ultimate sinks for Polychlorinated Biphenyls (PCBs). A three-dimensional hydrodynamic-ecosystem-PCB coupled model was applied to the Sea of Japan (SoJ), where deep water is isolated from the surrounding oceans, to elucidate the accumulation processes of CB153 and assess the contributions of physical and biological processes to the accumulation. We suggest that the dissolved CB153 concentration formed a three-layer vertical structure in the SoJ: the highest concentration is in the intermediate layer (100–600 m), followed by those in the deep (600 m to the bottom) and surface layers (0–100 m). Different accumulation mechanisms in the northern and southern SoJ were discovered. The oceanic biological pump enhances the accumulation in the northern SoJ by taking CB153 out of the thermocline in summer and contributes 70 % to the accumulation in the intermediate layer; while the vertical advection contributes 70 % to the accumulation in the intermediate and deep layer in the southern SoJ.

Distribution of pacific cod Gadus macrocephalus (Gadidae) and functional structure of the habitat in the northern Japan Sea and some issues on regulation of the fishery

Seasonal and bathymetric distribution of the main age groups of pacific cod in the northern Japan Sea are considered on the data of bottom trawl surveys in 1980–2023. The main wintering and spawning accumulations, where the fish concentrate from December to January and then spawn in February-March, are formed on the external shelf and the upper continental slope along the western coast approximately between Peter the Great Bay and 47о N and along the eastern coast between Cape Krillon and 47о 30′N. The juveniles have feeding migrations from April to May, while older age groups complete the migrations a month later. They migrate in three main directions: from the areas at the mainland coast – southwestward and northeastward and from the areas at western Sakhalin — southward. The juveniles feed on shallows in Peter the Great Bay, northern Tatar Strait, and on southwestern shelf of Sakhalin between the Nevelsky Bay and Cape Krillon, whereas the feeding grounds for older groups occupy two vast areas including Peter the Great Bay with the adjacent southeastern shelf of Primorye and the shelf of northern Primorye in the Tatar Strait (to the north from 47о N) with the whole shelf of Sakhalin. In the northern Tatar Strait (northward from 48о N), the cod belonged to the Primorye and Sakhalin stocks can feed together. The feeding season lasts from June to September. The older cod feed usually deeper that the juveniles. Back migrations of cod for wintering occur from October to November. Because of a joint feeding area where the mainland and Sakhalin stocks are able to mix, the bottom trawl surveys at Primorye coast cannot be used for correct assessment of the total available catch (TAC) in this fishing district. To improve quality of the cod fishery forecasts, the methods of cohort or production analyses should be used, with the control by bottom trawl surveys data, as alternative information about the state of cod stocks, taking into account the abovementioned patterns of seasonal distribution and migrations.

The presence of Ixodes pavlovskyi and I. pavlovskyi-borne microorganisms in Rishiri Island: an ecological survey.

Understanding the ecology of ticks and tick-borne microorganisms is important to assess the risk of emerging tick-borne diseases. Despite the fact that the Ixodes pavlovskyi tick bites humans, we lack information including population genetics and the reason for the inadequate distribution in Japan. A 5-year survey revealed that Rishiri Island, the main stopover in the East Asian Flyway of wild birds in the northern Sea of Japan, was a refuge of I. pavlovskyi. The I. pavlovskyi included two haplogroups, which were supposed to diverge a long time before the island separated from the continent and Hokkaido mainland. The detection of microorganisms from wildlife revealed that wild birds and rodents play a role in diffusion and settlement, respectively, of not only I. pavlovskyi but also I. pavlovskyi-borne microorganisms including Candidatus Ehrlichia khabarensis and Babesia microti US lineage. Various island-specific factors control I. pavlovskyi dominance and tick-borne pathogen maintenance. The results may enable us to explain how tick-borne infectious microorganisms are transported.

Spatiotemporal variation in the size structure of the chub mackerel, Scomber japonicus, over half a century in the East Asian Marginal Seas

The size and age structure of a population are crucial aspects for understanding population dynamics. Many marine fish species have experienced long-term reductions in size and age owing to overfishing and/or global warming; however, these aspects remain unexplored. The present study elucidated the spatiotemporal variations in chub mackerel size and age structure based on the operational reports of large- and medium-sized Japanese purse seine fisheries for nearly half a century. Our results revealed size- and age-dependent segregation at a fine spatial scale, which may indicate ontogenetic niche shifts in response to thermal and feeding conditions or intercohort competition. On a long-term temporal scale, a significant reduction in size and age was observed in the East China Sea, whereas a contrasting increase in size and age was observed in the northern Sea of Japan. This may indicate that large fish have greater sensitivity to global warming and shift their distribution more rapidly northward than do small fish. In addition, the reduction in size and age during the spawning season in the East China Sea may result in a bias towards younger spawners, potentially rendering population dynamics more unstable. This study highlights the importance of investigating the spatiotemporal variation in the size structure of exploited fish stocks.

Shedding light on a species complex within the genus Goniodoridella Pruvot-Fol, 1933 (Nudibranchia: Goniodorididae), with the description of three new species

ABSTRACT Goniodoridella Pruvot-Fol, 1933 is a genus of small nudibranchs found in the Indo-Pacific Ocean. Currently, the genus includes only two described species, the widely distributed type species Goniodoridella savignyi Pruvot-Fol, 1933 and G. borealis Martynov, Sanamyan & Korshunova, 2015, which is found in the northern Sea of Japan. However, because of the presence of a group of cryptic species, the known geographic range of G. savignyi may have been overestimated, while the species richness of the genus may be underestimated. In the current study, we examined specimens from Australia, the Philippines and Russia that were identified as G. savignyi, G. borealis and an undescribed species. Detailed analyses of the external morphology and internal anatomy of the specimens were carried out, as well as scanning electron micrography of the radula and the labial cuticle. Photographs of the penial spines were taken under a light microscope. DNA sequence data for selected mitochondrial and nuclear markers were obtained, allowing the inclusion of the genus Goniodoridella in molecular phylogenetic analyses for the first time. Our results support the monophyly of the genus Goniodoridella and confirm the existence of a species complex of which the type is G. savignyi. The new species G. geminae n. sp., G. serrata n. sp. and G. unidonta n. sp. are described.

Diapycnal Mixing and Double Diffusion over the Continental Slope in the Northern Sea of Japan in the Warm Half-Year

Diapycnal Mixing and Double Diffusion over the Continental Slope in the Northern Sea of Japan in the Warm Half-Year

Diapycnal Mixing and Double Diffusion over the Continental Slope in the Northern Sea of Japan in the Warm Half-Year

This study investigates double diffusion processes responsible for diapycnal mixing in the Primorye current in the northern Sea of Japan. The results of processing and analysis of a long time series of data from regular Aqualog-profiler measurements of thermohaline characteristics and current velocity over the continental slope between the horizons of 60 and 420 m from April to October 2015. Using the Osborne-Cox parameterization (1972) and Gregg’s (1989) parameterization, we estimated heat and salt diffusivities, as well as the buoyancy flux. To reveal the processes of double diffusion, the Turner angle was estimated. We estimated contributions of diffusive convection and salt fingers into the buoyancy flux. Due to double diffusion, the intense vertical mixing covered the layer from 80 to 170 m. From mid-spring to early May, diffusive convection penetrated to a horizon of 250 m, and then a process like salt fingers played a leading role. Shear instability caused by the weakly nonlinear interaction of internal waves prevailed in the underlying layers.

Relationship between environmental conditions and biennial growth of kelp Saccharina japonica var. ochotensis, northern Hokkaido, Japan

The kelp Saccharina japonica var. ochotensis occurs in the northern Sea of Japan. A monthly diving survey was conducted at two sampling stations, Tsugaru in Rebun Island and Hourai in Wakkanai district in northern Hokkaido, Japan, from March 2013 to November 2014. Oceanographic conditions, water temperature, nitrate, and irradiance were recorded, and several differences were observed between Tsugaru and Hourai. Higher irradiance at Tsugaru during July and August led to enhanced photosynthesis by sporophytes, and the lower temperature in this area led to increased storage of mannitol from April to September, with more sulfated polysaccharide in sporophytes and greater blade thickness compared to kelp specimens at Hourai. Higher water temperatures in Tsugaru during September and February led to larger sporophytes, whereas lower winter water temperatures in Hourai led to smaller sporophytes. Higher water temperatures from September to February and lower nitrate concentrations throughout the year except in April 2013 and March 2014 in Tsugaru were associated with higher sorus formation rates and lower regeneration (transition from annual to biennial sporophytes) rates than at Hourai. Irradiance at Tsugaru was higher than at Hourai from July to August. Lower temperatures and lower radiation result in a lower rate of sorus formation; whereas higher nitrate concentrations give rise to higher rates of regeneration.

The Stratosphere-to-Troposphere Transport Related to Rossby Wave Breaking and Its Impact on Summertime Ground-Level Ozone in Eastern China

In summertime, eastern China experiences severe ozone pollution. Stratosphere-to-troposphere transport (STT), as the primary natural source of tropospheric ozone, may have a non-negligible contribution to ground-level ozone. Rossby wave breaking (RWB) is a leading mechanism that triggers STT, which can be categorized as anticyclonic wave breakings (AWBs) and cyclonic wave breakings (CWBs). This study uses an objective method to diagnose AWBs and CWBs and to investigate their influence on the surface ozone in eastern China using ground-based ozone observations, satellite ozone data from AIRS, a stratospheric ozone tracer simulated by CAM-chem, and meteorological fields from MERRA-2. The results indicate that AWBs occur mainly and frequently over northeast China, while CWBs occur mostly over the northern Sea of Japan. STTs triggered by AWBs mainly have sinking areas over the North China Plain, increasing the ground-level ozone concentrations by 5–10 ppbv in eastern China. The downwelling zones in the CWBs extend from Mongolia to the East China Sea, potentially causing an elevation of 5–10 ppbv of ozone in both central and eastern China. This study gives an overview of the impacts of AWBs and CWBs on surface ozone in eastern China and helps to improve our understanding of summertime ozone pollution in eastern China.

Sediment depositional pattern in the northern Japan Sea over the last 1200 ka and its linkages to orbital forcing

The semi‐enclosed marginal Japan Sea is sensitive to global changes and responds to orbital‐scale variability. Sediment core samples from Integrated Ocean Drilling Program Site U1423 were processed for detrital grain size and semi‐quantitative mineral analysis to assess the sediment characterization and depositional environment in the Japan Sea over the last 1200 ka. The mean grain data suggest the dominance of the silt size fraction over sand and clay in the whole period, while sand content increases dramatically between 600 and 150 ka. The end‐member energy modelling of grain size data suggests that sediment deposition took place under two energy conditions over the last 1200 ka. The low‐energy conditions observed during the middle Pleistocene transition (MPT) is mainly related to the wind deposition with the sediment characteristics being moderately to poorly sorted and coarse to nearly symmetrical skewed during global cooling and enhanced East Asian Winter Monsoon (EAWM) winds in the northern Japan Sea. Post MPT, periodic fluctuations between higher and lower energy conditions are observed, and the depositional environment is controlled by the EAWM wind, and precipitation intensity, glacio‐eustatic sea‐level changes and sea‐ice volumes. During the period, detrital sediments are poorly sorted and nearly symmetrically skewed, marked by the dominance of quartz, plagioclase and k‐feldspar. The spectral analysis grain size‐related data shows the presence of 228, 41 and 23 kyr orbital paced cycles, which are also observed in the Chinese Loess Plateau's normalized quartz mean grain size. This study is the first report of 228 kyr cycles from the Pleistocene Japan Sea sediments indicate that sediment deposition in the Japan Sea is associated with ~200 kyr eccentricity cycle as in the Chinese Loess Plateau.

Spatiotemporal Patterns of Sea Ice Cover in the Marginal Seas of East Asia

Using multisource sea ice fusion data, the spatiotemporal characteristics of sea ice cover were analyzed for the marginal seas of East Asia for the period 2005–2021. The results show that there were obvious differences in the beginning and end dates of the sea ice in the different sea areas. The northern Sea of Japan had the longest ice period, and Laizhou Bay and Bohai Bay in the Bohai Sea had the shortest ice period. The time when the largest sea ice extent appeared was relatively stable and mostly concentrated in late January to mid-February. There were obvious spatial differences in the duration of the sea ice cover in the marginal seas of East Asia. The duration of the sea ice cover gradually decreased from high latitude to low latitude and from nearshore to open seas. The annual average duration of the sea ice cover was more than 100 days in most of the Sea of Japan and approximately 20 days in most of Laizhou Bay and Bohai Bay. The melting speed was significantly faster than the freezing speed in the Bohai Sea and Yellow Sea, resulting in asymmetric changes in the daily sea ice extent in the two seas. The increasing trends in the maximum sea ice extent and total sea ice extent were 0.912 × 105 km2/10 yr and 0.722 × 107 km2/10 yr, respectively, from 2005 to 2013, both of which passed the significance test at the 0.05 level.

Age and growth of red tilefish Branchiostegus japonicus in two fishery grounds off the Kaetsu region, Niigata Prefecture, northern Sea of Japan

Age and growth of red tilefish Branchiostegus japonicus in two fishery grounds off the Kaetsu region, Niigata Prefecture, northern Sea of Japan

Decrease of winter cyclone passage over northern Japan due to the reduction in the regional cyclogenesis associated with cold air outbreak

AbstractIn East Asia, a strong winter monsoon and high baroclinicity cause enhanced cyclone activity, which has been the subject of intensive study. Despite the high frequency of genesis of mesoscale cyclones in this area, most of the studies on the decadal timescale have focused only on synoptic‐scale cyclones. To clarify the interannual variation of the passage of winter cyclones including synoptic‐scale and mesoscale cyclones over and around Japan, a tracking algorithm was applied to 62 winter seasons (December–March) from 1958/1959 to 2019/2020. During the study period, the passage of cyclones around northern Japan showed a decreasing trend. Most cyclones that pass around northern Japan are generated over the northern part of the Sea of Japan, which is an area where cyclogenesis has decreased during the study period. Weather pattern classification based on synoptic scale atmospheric conditions revealed that passage of upper‐level troughs and occurrence of lower‐level cold air outbreaks are the preferential conditions for cyclogenesis in this region. In addition, the intensity of the cold air outbreak in this region was weakened during the study period. These results suggest that changes in atmospheric conditions due to climate change have reduced mesocyclone genesis over the northern Sea of Japan, resulting in the reduction in the number of cyclones passing over and around northern Japan.

Temporal variability of plutonium in surface waters of the Sea of Japan

Long-term temporal variations of plutonium in Sea of Japan (SOJ) surface waters have been examined with the aim to better understand its behavior during several decades. The first observation is that 239,240Pu activity concentrations in surface waters of the SOJ during 1977–2019 were 6.5 ± 4.7 mBq m−3 in average, and 5.1 mBq m−3 as the median, whereas 137Cs and 90Sr activity concentrations decreased with time, except of the perturbation due to the 2011 Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Another observation is that sporadic high 239,240Pu activity concentrations occurred in the east Japan Basin, ranging from 1 to 39 mBq m−3. The spatial distribution of 239,240Pu activity concentrations in surface waters revealed that high 239,240Pu levels (>20 mBq m−3) occurred in 1994 in the northern SOJ, which was considered to be due to winter convection. To elucidate factors controlling the temporal variability of surface 239,240Pu levels in the SOJ, a relationship between surface 239,240Pu activity concentrations and vertical diffusion coefficients was examined. The results revealed that this relationship could be classified into two groups: one group did not show a change with increasing diffusion coefficient, while the other group showed a positive correlation. The vertical 239,240Pu distribution in SOJ waters suggests that the high surface 239,240Pu levels occurred due to the upwelling of cyclonic eddy. The rapid recycling of deeper plutonium occurred in the SOJ due to deep winter convection and upwelling associated with cyclonic eddy. The plutonium levels in the SOJ have been found to be sensitive to climate changes. Warming of the SOJ may cause a reduction of winter convection and eddy activity as a result of increasing sea surface temperature. This leads to a decline of recirculation of plutonium and other bioavailable elements from Japan Sea Proper Water (JSPW) to surface water layers. Plutonium would be, therefore, an important indicator of biogeochemical processes in the marine environment, helping to assess climate change impacts on marine ecological systems.

The first description of larvae and comments on the taxonomy of Stichaeus ochriamkini Taranetz, 1935 (Perciformes: Stichaeidae).

Stichaeus ochriamkini (Stichaeidae) is common in the northern Japan Sea and the southern Okhotsk Sea. Among the five known representatives of the genus Stichaeus, early ontogenesis is the least studied in S. ochriamkini. In this study, the authors provide the first description of all larval stages of this species. In the north-western Japan Sea, larvae are found in plankton from early April to early June. S. ochriamkini larvae can be identified using the following characters: postanal-lateral pigment (PLP) lines present on the sides of the caudal part of the body and run along the anterior edge of hypaxial myomeres; 14-15 abdominal vertebrae; 32-34 rays in the anal fin; larvae disappear from plankton at a body length of LT > 25.0 mm (LS > 20 mm). Larvae of S. ochriamkini are very similar to larvae of Stichaeus punctatus. The melanin pigmentation in larvae of both species shows similar patterns of development. In the genus Stichaeus Reinhardt, 1836, two groups of species are distinguished by the presence/absence of PLP lines in larvae, and by significant divergence (clearly exceeding the species level) in the COI mtDNA gene. It is suggested the differences between these species groups is recognized at the generic level. Thus, the genus Stichaeus Reinhardt, 1836 should include S. punctatus and S. ochriamkini, whereas the other three species should be placed in the genus Dinogunellus Herzenstein, 1890: Dinogunellus fuscus, Dinogunellus nozawae and Dinogunellus grigorjewi.

Long‐term translocation explains population genetic structure of a recreationally fished iconic species in Japan: Combining current knowledge with reanalysis

AbstractAyu (Plecoglossus altivelis altivelis) is an important freshwater fisheries resource and popular recreational fishing species in Japan that lives for only 1 year, with a single breeding season. To supplement increased recreational fishing demand for this species, more than 13 million wild‐born landlocked juveniles are translocated every year from Lake Biwa into Japanese rivers, and more than 52 million hatchery‐reared juveniles born from captive‐reared parents have been extensively released. The translocation of landlocked juveniles and hatchery release has continued for more than 100 and 30 generations, respectively. Previous studies have reported that landlocked and amphidromous forms of Ayu easily hybridise, leading to concerns that the fitness of hybrid progeny would be reduced in the wild. However, limited information exists regarding the reproductive success of landlocked Ayu in translocated rivers, and to date no studies have evaluated the effects of translocation on population structure. Demonstrating that hybridisation occurs between the two forms is central to future management and conservation of this species. To address this, a literature search to summarise biological knowledge of Ayu and population genetic data screening was undertaken, and published genetic data sets covering a distribution range in Japan were reanalysed. Analyses provide strong evidence for very high gene flow between sampling locations. Genetic diversity is homogeneous in amphidromous samples. Bayesian admixture analysis infers widespread hybridisation in Japanese rivers (24 ± 8%). Maximum likelihood admixture graphs detect two migration events from Lake Biwa to rivers in the northern Sea of Japan and Hokkaido. Analyses consistently indicate that hybridisation between translocated landlocked juveniles and native amphidromous Ayu occurs throughout Japanese rivers. These results are discussed in relation to the management of this species.

Contour variations and acoustic characteristics of whistle sounds emitted by Pacific white‐sided dolphins in shallow coastal waters of the Sea of Japan

AbstractPacific white‐sided dolphins, Lagenorhynchus obliquidens (PWSDs), migrate along the coast of Japan. PWSDs rarely emit whistles, instead utilizing pulses, unlike many other delphinid species that frequently emit whistle sounds. In the present study, we aimed to clarify the acoustic characteristics and repertoire of the whistle of PWSDs, which have not been reported so far. We analyzed PWSD whistle sound systems (e.g., acoustic parameters and contours) during boat surveys and using passive acoustic monitoring in shallow coastal waters in the northern Sea of Japan. PWSDs in Shakotan rarely emitted whistles, while the burst pulse frequently was as reported in previous studies in other waters. The PWSD whistle vocalization rates were higher during traveling than during foraging. The frequency and duration of their whistles did not appear to change between behaviors. Although complex multiloop whistles were not recorded, whistle contours were classified into seven types. Whistles are often recorded intensively in a short period as a sequence or bout. Considering the extremely low whistle vocalization rates, dolphins may choose whistles instead of pulsed sounds in limited contexts. Our results shed light on the differences in whistle sound usage within odontocete species.

Freshwater and brackish water fishes of Sakhalin Island (Russia) in inland and coastal waters: an annotated checklist with taxonomic comments.

Based on a critical analysis of scientific publications for the last 200 years and on the collected specimens, a complete annotated list of both typical freshwater ichthyofauna of Sakhalin Island, with the inclusion of marine species that can be found in brackish coastal waters, is reported for the first time. The annotated list includes 226 species classified in three classes, 26 orders, 68 families, 29 subfamilies, and 148 genera. For 160 species, information is provided on collection samples deposited in various museums around the world, 36 of which are type specimens. For each species, conservation status (according to IUCN Red List of Threatened Species and the Red Book of the Sakhalin region), zoogeographic characteristics (distribution within Sakhalin Island and globally), abundance and commercial value are given. For a number of species, more detailed information on synonymy and nomenclature is provided. The study area is located in the western North Pacific and includes the entire coast of Sakhalin Island in the Sea of Okhotsk and the northern Sea of Japan, as well as the adjacent Sea of Okhotsk coast of northern Hokkaido, Japan.

Interannual dynamics of size, age composition and parameters of growth for japanese sardine <i>Sardinops melanostictus</i> in periods of its high abundance in the North-West Pacific

Interannual dynamics of size composition, age structure, and growth parameters are considered for japanese sardine Sardinops melanostictus in context of its recent and previous blooms and mass migrations to the Pacific waters at Kuril Islands and to the northern Japan Sea. Before the post-bloom catastrophic decline in the 1990s, in conditions of the highest density of the sardine population, small-sized fish with relatively slow growth rate became dominant, distinguished by lowered reproductive potential because of low population fecundity and reproduction rate. In the new, modern bloom of sardine population, two modal groups are observed in the year-classes size composition, in particular in the Japan Sea, with different exterior and biological parameters. There is assumed that they correspond with two morphological types, which alter each other at different stages of the demographic cycle, that determines total abundance of sardine population in the North-West Pacific and its long-term dynamics.