Wakasa Bay Research Articles

Annual net production of the five Sargassaceae species in Yoro, western Wakasa Bay, Sea of Japan

Annual net production of the five Sargassaceae species was investigated in Yoro, western Wakasa Bay, Sea of Japan. The Sargassaceae species were collected at a depth of 2.0–2.5 m and subjected to stratified clipping for 13 months. Annual net production was estimated at 2407 g dry wt/m2 for Sargassum patens, 2132 g dry wt/m2 for Sargassum macrocarpum, 1458 g dry wt/m2 for Sargassum siliquastrum. 1197 g dry wt/m2 for Myagropsis myagroides, and 1471 g dry wt/m2 for Sargassum piluliferum. The ratio of annual net production to maximum biomass (P/Bmax) for these species ranged between 1.3 and 1.7, being higher than in previous studies which used the same method. Winter storms with strong wave exposure and relatively calm condition in Yoro were considered to augment P/Bmax. The total losses estimated from the different units of stratified clipping were compared. If larger and less segregated units were applied, the total loss would decrease. It was suggested that a 50 cm stratum would be applicable to the larger species (3 m or longer) and a stratum of 20 cm or less would be applicable to mid-sized or smaller species (less than 3 m).

Genetic polymorphism of the adult medusae invading an electric power station and wild polyps of Aurelia aurita in Wakasa Bay, Japan

A large quantity of the jellyfish, Aurelia aurita, invade cooling water systems and cause serious problems at several electric power stations in Japan. In the present study, we examined intra—species genetic variation of A. aurita in Wakasa Bay, Japan in order to estimate the original polyp habitat of the adult medusae invading electric power stations. Total DNA was extracted from the adult medusae and the wild polyps, and polymerase chain reaction (PCR) was performed using the specific primers for amplification of nuclear internal transcribed spacer one (ITS-1) and mitochondrial cytochrome oxidase c subunit 1 (CO1). Then the DNA sequences of the PCR products were compared. The results showed genetic polymorphism of A. aurita in Wakasa Bay and locally specific frequency of each haplotype. The haplotype frequency, especially in CO1, of the adults collected at one of the power stations in Wakasa Bay was similar to that of the polyp colonies at harbours in the embayed area, not at another harbour in the western entrance of the bay. The polymorphic analysis is, therefore, thought to be useful for the determination of original polyp habitat as source of the adult medusae in relatively limited regions such as Wakasa Bay.

Directed movements and diel burrow fidelity patterns of red tilefish Branchiostegus japonicus determined using ultrasonic telemetry

Wild red tilefish Branchiostegus japonicus were tracked and/or monitored for up to nearly 3 months in Western Wakasa Bay and Maizuru Bay, Japan, using ultrasonic telemetry to examine their movements and burrow fidelity patterns. In Western Wakasa Bay, it is guessed that fish released in relatively shallow waters, about 30 m deep, actively moved into more suitable deeper habitats after their release. In Maizuru Bay, the fish did not undertake large-scale movements and showed burrow fidelity about 1 month after their release. That is, the fish primarily remained in the burrow, which was constructed in the sea-bottom, during the night and moved outside the burrow during the day. The marked circadian rhythm from Fourier analysis indicated a clear diel movement pattern of the red tilefish.

DEVELOPMENT OF 1-D CLOUD MICROPHYSICS DATA ASSIMILATION SYSTEM (CMDAS) BY USING AMSR-E DATA

In this paper, an 1-D Cloud Microphysics Data Assimilation System (CMDAS) is developed for retrieving reasonable cloud distribution. The general framework of CMDAS includes the Kesslerwarm-rain cloud microphysics scheme, a microwave radiative transfer model in the atmosphere and a global minimization method of Shuffled Complex Evolution (SCE). The paper investigates potentials of the CMDAS to modify the cloud properties by considering integrated cloud liquid water content as a assimilation parameter and to introduce the heterogeneity into the initial state of the atmosphere, by applying the CMDAS to the satellite microwave radiometer data set obtained by the international cooperative observation experiment, “Wakasa Bay Experiment 2003”, in Japan. The simulated microwave brightness temperature by CMDAS is in good qualitative and quantitative agreement with the observed one.

Influence of mass release of hatchery-reared Japanese flounder on the feeding and growth of wild juveniles in a nursery ground in the Japan Sea

The feeding and growth of wild juvenile Japanese flounder Paralichthys olivaceus (Temminck et Shlegel), collected after experimental mass releases of marked hatchery-reared juveniles of the same species, was examined at Wada Beach, Wakasa Bay, the Japan Sea, in 1997 and 1998. The feeding and growth of wild juveniles in the eastern area where the hatchery-reared juveniles were released and recaptured were compared with those in the western area (control area) where no hatchery-reared juveniles were recaptured. The stomach contents of both hatchery-reared and wild juveniles collected in the eastern and western areas consisted mainly of mysids in the early season (late-May to mid-June), and fish larvae in the late season (late-June to early July) in both 1997 and 1998. The stomach content index (SI) of juvenile flounder collected in the eastern and western areas showed that the feeding conditions followed similar patterns. However, the percent of empty stomachs in the wild flounder juveniles collected within 4 days after the mass release in the eastern area was as high as 10–30% in 1997 and 40% in 1998, whereas it was 0% in the western area in both years. Otolith microstructure analysis showed that the growth rate in the eastern area was not significantly different before and after release in both years. These results demonstrate that the mass release of hatchery-reared juvenile flounder temporarily affects the feeding efficiency of the cohabiting wild juveniles, but not to an extent that significantly reduces the growth rate.

Reproductive characteristics of Japanese anchovy, Engraulis japonicus, in two bays of Japan

Abstract The reproductive characteristics of Japanese anchovy, Engraulis japonicus , were studied in Osaka Bay and Wakasa Bay, which are located on each side of Japan. The length of spawning season varied between two bays: 8 months (between April and November) in Osaka Bay and 4 months (between May and August) in Wakasa Bay. The seasonal temperature profiles suggested that not only the onset of spawning in both bays but also the end of spawning in Osaka Bay are highly temperature-dependent, and that the critical temperature is about 15 °C. On the other hand, Osaka Bay anchovy collected after July were composed of only small ones (smaller than 10.5 cm body length). A comparison of length–weight relationships revealed a better body condition of small Osaka Bay fish than Wakasa Bay fish. It is likely that the Japanese anchovy in Wakasa Bay ceases spawning as early as September in spite of a high temperature, due to their poor nutritional condition. Estimated spawning frequency ranged from 0.40 to 0.88 for Osaka Bay females and from 0.22 to 0.62 for Wakasa Bay females. These values indicate that the Japanese anchovy from two bays spawn at similar intervals of 1.13–2.50 and 1.61–4.55 days. The sizes at first maturity in Osaka Bay and Wakasa Bay were estimated as 7.38 and 8.53 cm, respectively. These reproductive characteristics are compared and contrasted with those described for the Japanese anchovy in Sagami Bay.

Diurnal Variations of Snow Precipitation in Wakasa Bay during Winter

The diurnal variation of snow precipitation in the west coastal area near Wakasa Bay has been investigated for two winter seasons of 2001 and 2003 using surface precipitation radar, rain gauge, and satellite infrared data. Radar reflectivity-derived precipitation intensity shows a clear diurnal cycle within Wakasa Bay for both years, although the cycle is clearer in 2001 than in 2003. The precipitation maximum occurs in the early morning, and the minimum occurs in the evening. Using radar data collected during January 2003, the precipitation diurnal cycle within the Bay is compared with three nearby regions: offshore—open water region to the north, inland—land region to the northeast, and inshore—coastal region to the northeast. It appears that all the other three regions have the precipitation maximum during the day and the minimum during night, although the diurnal variation inland (over land) is very small. Additionally, in the offshore region, there exist two precipitation maxima and minima during a 24-hour day. Analysis of precipitation data from AMeDAS (Automatic Meteorological Data Acquisition System) rain gauge stations basically agrees with the radar observations. It shows that a similar diurnal cycle, found in the radar data within Wakasa Bay, can also be found for coastal stations, although the different patterns are shown depending on the location and time period in 2003. When averaging data from both January and February during 2001 and 2003, the diurnal cycle tends to be smoothed out. Cloud top temperature and cloud fraction derived from satellite infrared data do not show a clear diurnal cycle within Wakasa Bay, nearby inshore and inland regions, although the decreases of brightness temperatures are seen around noon in the offshore region for both cases of 2001 and 2003. Analysis using collocated satellite and radar data indicates that cloud top temperature has little skill in reflecting surface precipitation for the winter convective clouds associated with cold air outbreaks. Finally, possible causes of the diurnal variation are discussed, including local land-sea breeze and mountain wind effects, as well as the radiative cooling effect.

A method of studying fish behavior using underwater acoustic biotelemetry ～Tracking of the red tilefish released in the Wakasa Bay and the Maizuru Bay～*1

A method of studying fish behavior using underwater acoustic biotelemetry ～Tracking of the red tilefish released in the Wakasa Bay and the Maizuru Bay～*1

Distribution of snow crab, Chionoecetes spp., larvae off Wakasa Bay in the Sea of Japan

ABSTRACT: The distribution of snow crab, Chionoecetes spp., larvae was studied by horizontal plankton net tows using a multiple opening/closing nets and environmental sensing system from the surface to the bottom off Wakasa Bay (approx. 500 m) in the Sea of Japan. The hatching season was concluded to occur between early February and late April with a peak occurring in March. First zoeae occurred most densely in March, second zoeae in April, and megalopas between April and June within the Tsushima Warm Current (0–200 m). The temperature of the strata at which more than 88% of each stage of larvae were distributed varied from 8.4 to 15.0°C. As the larval stage progressed, they gradually moved to deeper water strata. In and after June, megalopas observed in the premolt stage started a downward migration beyond the thermocline to the cold bottom water (water proper to the Sea of Japan, <5°C all year round). Therefore, the settlement of megalopas and metamorphosis to the first benthic stage was concluded to occur in June. The second zoeae and megalopas underwent diurnal vertical migrations. The durations of the first and second zoeal stages and the megalopal stage were estimated at approximately 20 days, 20 days, and 60 days, respectively.

Wavelength‐dependent aerosol single‐scattering albedo: Measurements and model calculations for a coastal site near the Sea of Japan during ACE‐Asia

Wavelength‐dependent optical properties together with the size‐resolved elemental and chemical composition of the atmospheric aerosol were measured at Yasaka, Japan, near Wakasa Bay on the coast of the Sea of Japan. Observations were performed as part of the Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) campaign during three weeks in March and April 2001. Information about the detailed chemical composition and the size distribution of the aerosol, including absorbing material, was used to model optical properties of the aerosol and compare them with directly measured properties. Continuous, size‐resolved measurements of aerosol scattering and backscattering coefficients were made at wavelengths of 450, 550, and 700 nm. Aerosol size distribution measurements were taken three times during the campaign for a period of 3–4 days each, using cascade impactors. One of the measurement periods was influenced by an intense yellow dust event originating on the Asian continent (20–25 March 2001), while the other two data sets were only weakly influenced by dust particles. The size‐resolved measurement of aerosol scattering coefficients and the chemical analysis showed that the dust was accompanied by fine accumulation‐mode particles during the dust event. The effects of the mineral dust particles on the optical and chemical properties of the aerosol are discussed, and data sets with and without desert dust influence are compared. Before the optical closure calculation a mass closure of the aerosol was performed, and the influence of the nonanalyzed fraction on the calculated optical properties of the aerosol is investigated. In general, good agreement between measured and modeled aerosol optical properties was found for the aerosol scattering and absorption coefficients, while less agreement was found for the backscattering coefficients, especially for the coarse mode of the aerosol. A distinct difference between the dust and nondust periods was found for the wavelength‐dependent single‐scattering albedo.

Field evaluation by RNA/DNA ratios on post-release nutritional status of released and wild Japanese flounder Paralichthys olivaceus juveniles

A large-scale juvenile Japanese flounder ( Paralichthys olivaceus) release–recapture experiment was undertaken to find the optimal release season by evaluating the nutritional status of released fish at different seasons during which food abundance was significantly different. Forty thousand fish were released at depths of 1.5 m for early-release (May 29, 1997) and 2 m for late-release (July 2, 1997) (42.1±3.5 and 40.9±4.2 mm body length, respectively) in an experimental field, Wakasa Bay, the Sea of Japan. Samples were taken, after the releases, at Wada beach at intervals of 1, 2, 3, 6, 10, 16 and 30 days after release (DAR), including pre-surveys before each release. Released fish recaptured from the two different release groups totaled 764; 467 from the early-release group (ER) and 297 from the late-release group (LR). A total of 1956 wild flounder juveniles were simultaneously collected (1041 ER, 915 LR). ER fish were subject to higher food availability and were exposed to less pressure from predation by smaller wild juvenile flounder. RNA/DNA ratios in ER juveniles were significantly higher than those of LR fish during all samples. Especially, RNA/DNA ratios in ER juveniles were higher than in wild juveniles from 3 to 50 DAR. In the LR group, the nutritional status of juveniles was relatively low in shallower water. These findings corresponded well with feeding incidence examined by coworkers. Mass release of hatchery-reared juveniles apparently reduced RNA/DNA ratio of the wild juveniles right after releasing. The present study showed that earlier release of hatchery-reared juvenile Japanese flounder with higher RNA/DNA ratio could increase the possibilities of survival right after release in the nursery ground, and that RNA/DNA ratio appeared to be a good tool in evaluating nutritional status of released juveniles as well as wild juveniles in Japanese flounder.

Geographical structure of morphological characters in Semanotus japonicus (Coleoptera: Cerambycidae) in Japan

The sugi bark borer, Semanotus japonicus, occurs naturally in Honshu, Shikoku, Sado Is., Oki Is., and Yaku Is. in Japan, and its main host tree is the Japanese cedar, Cryptomeria japonica. Because of a correspondence between the present distribution of geographical variation in the borer and the refugia of the Japanese cedar during the last fullglacial period, isolation of the cedar is thought to have caused differentiation in the borer between local populations. In this study, we used morphological information to elucidate the geographical differentiation of S. japonicus populations. Multivariate analyses were performed based on ten morphological characters for ten populations. Populations between the Pacific coast side and the Wakasa Bay area showed remarkable variation in morphological characters. Because the distribution of the refugia of the cedar coincided with the patterns of morphological variations in S. japonicus, it is suggested that the geographical structure of the present S. japonicus population was caused by isolation during the last glacial period. While vicariance is no longer a factor with the expansion of C. japonica’s distribution, its past effects may have been important enough to influence the present genetic structure of S. japonicus.

Developmental change in RNA: DNA ratios of fed and starved laboratory‐reared Japanese flounder larvae and juveniles, and its application to assessment of nutritional condition for wild fish

Starved Japanese flounder Paralichthys olivaceus larvae were characterized by relatively lower levels of RNA content throughout their early life stages. Significant differences in the RNA: DNA ratios were found between fed and starved fish, and appeared to increase as starvation proceeded. Ontogenetic changes in RNA: DNA ratios were clearly observed during metamorphosis, especially decreasing during the period from the late‐metamorphic to postmetamorphic stages. The criteria established from these laboratory experiments, were applied to the nutritional condition of wild larvae and juveniles collected in Wakasa Bay, Sea of Japan in 1994 and 1995 by measuring RNA and DNA content. Starved fish were mainly found in stage I (settling stage) fish during the late season of settlement in 1995. This suggests that starvation could be associated with settlement in Japanese flounder.

A NUMERICAL SIMULATION OF WIND FIELD OVER THE LAKE BIWA

A wind field over the Lake Biwa is very complex and variable since the wind field is influenced by sea and land breezes from Osaka, Ise and Wakasa Bays, and the Lake Biwa is surrounded by mountains. In this study, we conducted a three-dimensional numerical simulation of the wind field with HOTMAC of a mesoscale meteorological simulation model. And we verified the numerical simulation method by making a comparison between calculated result and some preceding observational data and examined a relationship between the wind field and the extended sea breeze. The simulation result show that a northwest wind which is the most dominant wind system is caused by the sea breeze from the the Wakasa Bay and that the lake breese is strongly influenced by the extended sea breese.

Geographic Variations in Dorsal and Anal Ray Counts of Juvenile Japanese Flounder, Paralichthys olivaceus, in the Japan Sea

Meristic counts of early and late wild settled juveniles of Japanese flounder, Paralichthys olivaceus (Paralichthyidae), in Wakasa Bay, Japan, were compared, with specimens collected from 26 sites spread along ca. 1700 km of coastline facing the Japan Sea. Mean dorsal and anal ray counts of the early settled group at Kyoto were significantly larger than those of the late settled group. A discontinuous geographic boundary in mean dorsal and anal ray counts was found around Wakasa Bay and the Noto Peninsula with both means significantly larger in the southern group than in the northern group. Mean ray counts of the early and late settlers at Kyoto were similar to those of the southern and northern groups, respectively. The effect of water temperature on meristic characters was tested on two groups of laboratory-reared juveniles. Mean dorsal and anal ray counts were larger in juveniles reared at higher water temperatures. The early and late settler groups were estimated to hatch in late February and late April, respectively, representing negative response of meristic characters to water temperatures if these two groups hatched out in Wakasa Bay. Differences in the dorsal and anal ray counts between the early and late settled groups at Kyoto can, therefore be attributed to genotypic, not phenotypic variation. This suggests the possibility of transport of larvae of the early group from areas further south to Wakasa Bay by the warm Tsushima Current, a branch of the Kuroshio, which flows northeastward along the coast of the Japan Sea, particularly when the temperature gradation between the south and north areas during these seasons is considered.

Neoheterobothrium hirame sp. nov. (Monogenea: Diclidophoridae) from the Buccal Cavity Wall of Japanese Flounder Paralichthys olivaceus.

Neoheterobothrium hirame sp. nov.is described, based on specimens collected from the buccal cavity wall of Japanese flounder, Paralichthys olivaceus, caught in Wakasa Bay, Japan. The parasite was 14-33 mm in total length, with 4 pairs of clamps on the pedunculated haptor, which was separated from the body proper by a long isthmus. The presence of a pair of peripheral intestinal branches running along both sides of body, in addition to the main pair of medial branches, is described here for the first time.The new species can be distinguished from N. affine (Linton, 1898) --the most closely related species and the type species of the genus--by the relatively large body proper and the shorter isthmus. The taxonomic status of other related species is discussed. The generic diagnosis proposed by Price (1943), Yamaguti (1963) and Mamaev (1987) is emended.

The Current Structure of the Tsushima Warm Current along the Japanese Coast

The branching of the Tsushima Warm Current (TWC) along the Japanese coast is studied based upon intensive ADCP and CTD measurements conducted off the Wakasa Bay in every early summer of 1995–1998, the analysis of the temperature distribution at 100 m depth and the tracks of the surface drifters (Ishii and Michida, 1996; Lee et al., 1997). The first branch of TWC (FBTWC) exists throughout the year. It starts from the eastern channel of the Tsushima Straits, flows along the isobath shallower than 200 m along the Japanese coast and flows out through the Tsugaru Strait. The current flowing through the western channel of the Tsushima Straits feeds the second branch of TWC (SBTWC) which develops from spring to fall. The development of SBTWC propagates from the Tsushima Straits to Noto Peninsula at a speed of about 7 cm sec−1 following the continental shelf break with a strong baroclinicity. However, SBTWC cannot be always found around the shelf break because its path is influenced by the development of eddies. It is concluded that SBTWC is a topographically steered current; a current steered by the continental shelf break. Salient features at intermediate depth are the southwestward subsurface counter current (SWSCC) between 150 m and 300 m depths over the shelf region in 1995–1998 with the velocity exceeding about 5 cm sec−1, although discrepancies of the velocity and its location are observed between the ADCP data and the geostrophic currents.

若狭湾西部海域におけるヒラメの成熟

1992&acd;1998年に若狭湾西部海域で漁獲されたヒラメを試料とし, 生殖腺の成熟度とGSIから成熟の年齢およびサイズと産卵期を検討した。年齢別の成熟割合は, 雌では2歳で5%, 3歳以上で75%以上, 雄では1歳で5%未満, 2歳で5%, 3歳以上で80%以上と推定された。成熟最小全長は, 雌43cm, 雄32cmで, 雌は47cm, 雄は36cmをそれぞれ超えると50%以上が成熟すると推定された。産卵期は, 概ね2月下旬から6月上旬であり, その盛期は4&acd;5月と推察された。

The influence of environmental factors on early life history patterns of flounders

The near-shore migration and settlement phases of Japanese and American flounders of the genus Paralichthys are compared and discussed relative to differences in coastal environments. Field sampling was conducted in Wakasa Bay, Kyoto Prefecture, Japan, where the shelf is narrow, estuarine habitat limited and tidal range slight, and in Onslow Bay, North Carolina, USA, where the shelf is broad, estuarine habitat extensive and tide relatively strong. Distribution of larvae and juveniles suggests Japanese flounder spawn in close proximity to nursery grounds relative to flounder in Onslow Bay. Sampling of planktonic and benthic flounder just seaward of nursery grounds resulted in capture of a wide range of developmental stages in Wakasa Bay (early planktonic to juvenile), but was limited to metamorphosing larvae in Onslow Bay. Vertical distribution of larvae during the night also differed between the Bays. At night most larvae in Wakasa Bay remained near the bottom regardless of tidal stage. In contrast, larvae in Onslow Bay exhibited selective tidal stream transport. Laboratory experiments conducted to examine the behaviour of recently captured wild and laboratory-reared larvae indicated that wild flounder from Onslow Bay had an endogenous rhythm of activity that corresponded to the tide at the time of capture. In contrast, wild flounder from Wakasa Bay and laboratory-reared larvae showed no distinct activity pattern. These results suggest that physical characteristics of the environment influence the early life history patterns of flounders by modifying behaviour of migrating larvae.

Morphology and chemical composition of individual dust particles collected over Wakasa Bay, Japan

Morphology and chemical composition of individual dust particles collected over Wakasa Bay, Japan