Deepening and Evolution of a Low over the Sea of Japan in Late August in 2016: Interaction of Midlatitude Flows and Typhoon Lionrock (1610)

Effect of high temperature on gametogenesis of the sea urchin Strongylocentrotus intermedius in the Sea of Japan, northern Hokkaido, Japan

In July-August 2018, coastal observations of marine mammals were conducted at the mouth of the Tyvlinka River (Yekaterina Bay, Sakhalin Gulf) in the Sea of Okhotsk, Khabarovsk region. In total, 40 killer whale encounters were recorded, against 68 killer whale encounters during the same period in 2015. On the coastal strip from the mouth of the Tyvlinka River to Cape Litke there are three rookeries of true seals (largha and lakhtak), with a total number of about 300 individuals. During the period of field observations, two cases of killer whale attacks on seals were recorded. Satellite beacons were installed on three killer whales and on two belugas. These beacons made possible to monitor subsequent migrations of tagged animals during summer-autumn period of 2018. Two killer whales, tagged in the Akademiya Bay and the Konstantin Bay in August, remained in the area of Shantar Archipelago during the salmon run, then in late August - early September they moved to the open waters of the Okhotsk Sea to the area where fishery vessels harvested the demersal fish species. Female killer whale tagged in the Sakhalin Gulf migrated to the northern part of the Okhotsk Sea to the Shelikhova Bay and the Penzhinskaya Bay, and almost repeated in calendar dates and positions the track of another female killer whale that was tagged in the summer 2015. The average speed of killer whales ranged from 4.3 km/h to 8.6 km/h. Belugas are more attached to their habitats in the Sakhalin Gulf. One of tagged belugas remained in the Gulf of Sakhalin, the other passed through the Nevelskoy Strait in October and went into the Sea of Japan. The average speed of beluga whales was two to three times lower than in killer whales and ranged from 1.7 km/h to 2.5 km/h.

Sex structure, growth, maturing and spawning of clam Mercenaria stimpsoni at Primorye coast (Japan Sea) are considered on the data of histological analysis of gonad tissue preparations and gonad smears collected in diving surveys conducted eastward from Cape Povorotny in the summer-fall of 2006-2009 and 2012-2013. The mollusk dwells on sandy or muddy-sandy grounds at the depth to 20 m along the coast opened to surf waves. Its annual increments were identified in radial section of the outer layer of shell between the umbo and ventral margin. Its mature begins at the age 7-8 years with the shell length about 40 mm; all mollusks become mature at the age 10-11 years when their shell reaches the size 50-55 mm, so transition from juvenile to mature clam lasts about 3 years. The shell length of half-maturing is 43.5 mm that corresponds to the age 9-10 years. Males prevail among small-sized M. stimpsoni (40-44 mm) with the ratio 1.26 : 0.74, but the sex ratio is equal for the basic mature stock, and females prevail among large-sized clams with the ratio 0.70 : 1.30, so the sex ratio for the whole surveyed area is approximately equal. M. stimpsoni spawns there from mid-August to mid-September, with the mass spawning in late August - early September, under the water temperature 13-19оC.

Based on an analysis of the gonads, as well as the size composition and abundance of larvae in plankton, we determined the seasonal and long-term dynamics of the reproduction of the mussel Mytilus coruscus in Amursky Bay (Peter the Great Bay, Sea of Japan). Mussel gonads were in a mature condition in late July-early August; the spawning season continued from mid-August to mid-September. The larvae of this species occurred in plankton from June to September, under surface water temperatures of 14.5–23.5°C. The density of larvae in different years varied from 350 to 4500 ind/m3. Two peaks of larval abundance were observed annually, in June and September. The first peak was apparently provided by allochthonous larvae, the second, by larvae of the local population. The high density of larvae of M. coruscus in the plankton of Peter the Great Bay enabled us to consider this species as a potential object for mariculture.

The seasonal population size of planktonic larvae of mollusks of the soft-shell clam genus Mya were studied in Vostok Bay. The larvae occurred in plankton from the first third of June to early September. The highest density of larvae (279.7 ± 98.7 specimens/m3) was found in late June. In early July, larval numbers decreased sharply, and at the end of the first third of July, only single Mya larvae were found in the plankton. Another increase in larval population was observed in early and late August. The larvae varied in length from 175 to 325 μm in June–July and from 150 to 250 μm in August. It is likely that the larvae of two species of Mya, M. arenaria and M. uzenensis, are present in the plankton of Vostok Bay.

Unprecedented large-scale harmful algae blooms (HABs) were reported in coastal waters off the south-eastern coast of Hokkaido, Japan, in mid-to-late September 2021, about a month after very intense and extensive marine heatwaves subsided. To understand the physical–biological processes associated with development of the HABs, we conducted analyses via a combination of realistic ocean circulation models, particle-tracking simulations, and satellite measurements. The satellite-derived chlorophyll concentrations (SCCs) and areal extent of the high SCCs associated with the HABs were the highest recorded since 1998. More specifically, the extent of SCCs exceeding 5 or 10 mg m−3 started to slowly increase after 20 August, when the marine heatwaves subsided, intermittently exceeded the climatological daily maximum after late August, and reached record-breaking extremes in mid-to-late September. About 70% of the SCCs that exceeded 10 mg m−3 occurred in places where water depths were <300 m, i.e., coastal shelf waters. The high SCCs were also tightly linked with low-salinity water (e.g., subarctic Oyashio and river-influenced waters). High-salinity subtropical water (e.g., Soya Warm Current water) appeared to suppress the occurrence of HABs. The expansion of the area of high SCCs seemed to be synchronized with the deepening of surface mixed layer depths in subarctic waters on the Pacific shelves. That deepening began around 10 August, when the marine heatwaves weakened abruptly. However, another mechanism was needed to explain the intensification of the SCCs in very nearshore waters off southeast Hokkaido. Particle-tracking simulations based on ocean circulation models identified three potential source areas of the HABs: the Pacific Ocean east of the Kamchatka Peninsula, the Sea of Japan, and the Sea of Okhotsk east of the Sakhalin Island. Different processes of HAB development were proposed because distance, time, and probability for transport of harmful algae from the potential source areas to the study region differed greatly between the three source areas.

As the materials for this project, we used data on the distribution of the larvae of the Asian paddle crab Charybdis japonicus (A. Milne-Edwards, 1861); the spider crabs Hyas coarctatus ursinus (=Hyas ursinus) (Rathbun, 1924), Pugettia quadridens (de Haan, 1839), and Pisoides bidentatus (H. Milne-Edwards, 1873); the samurai crab Paradorippe granulata (=Dorippe granulata) (de Haan, 1841); the pea crab Pinnixa rathbuni (Sakai, 1934); and the porcelain crab Pachycheles stevensii (Stimpson, 1858) in Minonosok Bay of Pos’eta Bay obtained during 2000–2002 and in 2004. The planktonic samples were collected from the last third of May to September. The greatest density of the larvae was observed in May, mid-June, late June-early July, and late July-early August. The greatest densities of the crab larvae and the decapod larvae ranged from 20.4 to 48.2 and from 88.4 to 245.3 specimens/m3. The schedule of the crab larvae’s occurrence in the plankton is provided for the first time. The distribution of the density showed pronounced patchiness.

The long-term variation of 14C concentrations in atmospheric CO2 samples collected every 10 days was measured in the Ohkuwa area of Kanazawa, Ishikawa prefecture, Japan (36.3°N, 136.4°E), from April 1991 to December 2000. The 14C concentration decreased gradually by about 5‰ each year from 1991 to 2000, with a pronounced seasonal cycle which began to increase from spring and reached the maximum in late July or early August, followed by a decrease to the minimum from December to February. The appearance of large seasonal cycles and the extreme decrease of 14C concentration in winter seemed to be caused mainly by the air containing a large amount of 14C-free fossil fuel CO2 transported across the Sea of Japan from the Asian continent, not by the influence of local fossil fuel consumption.

Mid-water trawl surveys were conducted from late August to late September in 1999 and 2004 in order to investigate the distribution pattern, hatch date, and growth of juvenile Pacific bluefin tuna Thunnus orientalis in the Sea of Japan. Juveniles were collected at the stations where ambient water temperature (mean water temperature from surface to 30 m deep, WT0−30) was 23.4–25.9°C, and most of them were found in waters where WT0−30 was higher than 24°C. Sampled juveniles ranged 108–280 mm fork length. Based on otolith analysis, they were estimated to grow to approximately 180 and 250 mm at 60 and 90 days old, respectively, and showed similar growth to that of Atlantic bluefin tuna in the Mediterrannean Sea. The back-calculated hatch date of the samples was mostly in July and most juveniles spawned in the Sea of Japan.

The distribution and early growth of juvenile Pacific bluefin tuna (PBF) Thunnus orientalis were studied based on trawl surveys conducted around Sado Island, eastern Sea of Japan, from late August to early September in 2017 and 2018. Juvenile PBF were mainly collected in an area between the Tsushima Warm Current and land where the surface water (5-m depth) temperature ranged from 22.8 to 27.2 °C. The fork length (FL) of the fish ranged from 12 to 320 mm, and there were modes at 140–170 mm FL in the frequency distribution for both years. In 2018, there was also a mode at around 50 mm FL. Otolith microstructure analysis revealed that hatch date mainly peaked in early and mid July in both years, and in early and mid August in 2018, and corresponded with the modes of FL. In addition, differences in growth were observed between year classes, and between size classes in 2018. Total gill raker number increased with FL and was almost constant at around 100 mm FL. This study provides an update of the distribution of juvenile PBF in the Sea of Japan, which was found to be related to the Tsushima Warm Current, and indicates the importance of the eastern Sea of Japan as a nursery ground for PBF that hatch from July to August.

The aim of this study is to examine the development of four tropical cyclones (TCs) in the North Atlantic basin in late August and early September 2010. This period is of interest because four consecutive easterly waves emerged from West Africa and resulted in a multiple TC event (MTCE) over the North Atlantic. The first two TCs—Danielle and Earl—quickly developed into TCs east of 40°W and eventually intensified into major hurricanes. Conversely, the last two TCs—Fiona and Gaston—developed more slowly reaching only weak tropical storm intensity at their peak. The close proximity and differing evolution of these four TCs provides a unique opportunity to examine how these TCs interacted with each other and their surrounding environment, which influenced their development as they moved westward across the North Atlantic. The results showed that concurrent extratropical cyclogenesis events over the western and eastern North Atlantic and the recurvature of TC Danielle produced increased meridional flow over the midlatitude North Atlantic. This increased meridional flow resulted in subsynoptic-scale regions of increased vertical wind shear in the subtropics, which delayed Earl’s development and led to Fiona’s demise. Additionally, increased meridional flow in midlatitudes contributed to anomalous drying of the subtropics. This dry air was entrained into Gaston’s circulation leading to reduced convection and weakening. These TC–TC and TC–environment interactions highlight the difficult challenge of forecasting TC genesis and position posed by MTCEs in a rapidly evolving synoptic-scale flow.

Investigations were made on the infection dynamics of Neoheterobothrium hirame among wild 0-year-old Japanese flounder Paralichthys olivaceus caught in the western Sea of Japan off Tottori Prefecture from spring to autumn in 1999 and 2000. The infection shows the same tendency in both years; flounder became infected in June, a second parasite generation started to appear in early August, and both the prevalence of infection and mean parasite abundance increased thereafter, reaching 100% prevalence in October. One- to two-year-old infected flounder probably acted as the source of infection to the 0-year-old flounder. The parasite distribution showed an increasing overdispersion among 0-year-old fish population from July to August 1999, followed by a continuous decrease in overdispersion in the following months. Furthermore, only a few numbers of fish could be collected in late August to October. These suggest that parasite-induced host mortality occurred among the 0-year-old flounder in this period. In 2000, the parasite showed a similar overdispersed distribution among the 0-year-old flounder populations in late August, but the overdispersion was not clearly decreased afterwards. This is probably because very small-sized parasites were dominant in mid-October. The fish density was extremely reduced from October to November as in 1999. In a survey in August 2000, there was a tendency that severity of anemia was correlated with the intensity of infection. As a conclusion, it is highly probable that N. hirame contributed to the sharp decline in the 0-year-old flounder population in Tottori Prefecture in the autumn of 1999 and 2000.

Seasonal changes in the testis of the lined shore crab, Pachygrapsus crassipes, were examined histologically. The materials were obtained along the beach of Niigata City facing the Japan Sea, and the period of collection extended from April to November, 1969. The process of spermatogenesis was classified roughly into six stages. These are: primary and secondary spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa. The sperm is aflagellate, consisting of a spherical acrosome that is surrounded by a cup shaped nucleus with radiating processes. The acrosome is derived from the PAS-positive granules found in the cytoplasm of the spermatid during spermiogenesis. Further, the acrosome is provided with a proximal tubule and a structure of distal coronet. In April, the seminiferous tubule contains many residual sperms and a cluster of spermatogenetic cells in their earlier stages, such as secondary spermatogonia and primary spermatocytes. Some of the residual sperms are included in the cytoplasm of the nursing cells that form a simple layer of the columnar epithelium. The testes taken from the materials of May to June are filled with a lot of spermatocytes and spermatids. The highest peak of the testicular activity reaches in late July. Spent testes are found in some individuals obtained in late August, but spermatogenesis still continued to exist in a number of specimens obtained in late September to November, because the recovery phase takes place gradually.

This paper is based on 141 'light-house struck specimens'of Locustella o. ochotensis, sent to the writer from the following 17 light-houses since 1924: Kuriles (Kunashiri), Hokkaido (Erimo, Chikyu, Esan), Aomori (Hiradate, Oma, Shiriya), Akita (Nyudo), Chiba (Nojimazaki), Shizuoka (Omae), Wakayama (Hinomisaki), Shimane (Jizo, Hinomisaki), N. Kiushiu (Eboshi), S. W. Korea (Takeshima, Shichihatsuto) and Formosa (Fukikaku). Other specimen and sight records from Yamagata, Niigata, Saitama, Tokyo, Toyama, and S. Korea were also considered. Chief points are as follows:1) This less-known species passes Japan chiefly in June and late August to October. 2) The spring migration period (early v-vi) is much shorter than that of the autumn (late viii-xi). The breeding period is short (early vii-mid-viii) and the wintering period is five months (xii-iv). 3) The reason for more records in the autumn than in spring should be the tripled post-breeding population and high ratio of young bird accidentals. 4) Distinctly, the migration is heavier on the Japan Sea side than on the Pacific coast of Honshiu, and suggested three migration courses are: firstly, the well-known Philippine-Formosa-Riu Kiu course; secondly, the newly proposed one of Philippine-Formosa-China coast-S. Korea (across the Yellow Sea)-N. Kiushiu; and thirdly, continental course passing Ryojun (Port Arthar). The second is the chief route of this species. 5) More males (4 out of 5) than females were passing Cape Shiriya in early June (the 8th), which was reversed (6 females out of 7) in middle June (the 16th), and no male was included on the 27th. During this period, the measurements of the gonads of both sexes increased (faster in the males). 6) Three fat classes of amount were identified. In spring specimens, there was excess deposition of fat which is reserved to be used as energy for postmigration breeding. In the autumn, the fat was much less, and was more so in the young birds. 7) Both the rate of gonad development and amount of fat were rather constant among the birds of the same flock, but were different by flocks, irrespective of the advance of the season.