Oshima Island Research Articles

Surface circulation in Sagami Bay: the response to variations of the Kuroshio axis

In order to study the characteristics of the surface circulation in Sagami Bay, long-term current measurements were carried out at five moored stations during the period from October 1982 to January 1984. The majority of current patterns show the existence of a cyclonic eddy in the bay, while at times the direction of the circulation is reversed. When the Kuroshio current flows over the Izu-Ogasawara Ridge and approaches Sagami Bay, the current that passes through the Oshima-West Channel north of Oshima Island (COWC), has a strong clockwise flow, while the counterclockwise circulation in the bay becomes intensified. When the Kuroshio shifts southward off the shore, the COWC and the flow in the bay are weak or at times reverse their directions.

奄美大島のサトウキビに見出されたアザミウマ類

Surveys were conducted on the species composition and the relative abundance of thrips on sugarcane in Amami Oshima Island, Kagoshima Prefecture. Thrips were col-lectd from young leaves of sugarcane from May to November in 1988. Total samples consisted of 1324 specimens belonging to 9 species. Stenchaetothrips minutus and Fulmekiola serrata were the predominant species which taken together comprised 99. 1% of the total thrips collected. Although Haplotrips aculeautus is considered as one of the important pests of sugarcane, only a few individuals were collected in this investigation.

Pattern of Breeding‐System Change in the Izu Islands in Campanula punctata: Bumblebee‐Absence Hypothesis

Abstract Bagging experiments of Campanula punctata were carried out in natural populations on the six of the Izu Islands and mainland Honshu to investigate distribution of self‐incompatibility. Additional observations on pollinators of Campanula supplementary to the previous study (Inoue and Amano, 1986) were made. Most of the plants on Honshu and Oshima Island showed self‐incompatibility: while almost all plants in the Izu Islands except Oshima were self‐compatible. Bumblebees did not exist in the Izu Islands except Oshima and the dominant pollinators of Campanula in these islands were halictid bees. These results support a hypothesis that a decrease in pollination efficiency in the absence of bumblebees results in the evolution of breeding systems in Campanula.

Influence of volcanic eruptions on helium isotope ratios in hydrothermal systems induced by volcanic eruptions

Temporal variations of 3He 4HE and 4He 20Ne ratios occur in high-temperature gases from a steam well located about 3 km north of the central cone of Mt. Mihara, an active volcano in Oshima Island, Japan. The 3He 4He ratio gradually increased from 1.71 R atm (1.71 times the atmospheric ratio of 1.40 × 10 −6) in October 1986 to 5.02. R atm in November 1987. Taking into account a similar 4He 20Ne change, the magmatic He component in the steam has increased since the violent eruptions of Oshima volcano from November 15 to December 18, 1986. This confirms a direct relationship between magmatic activity and elevated 3He 4He ratios in groundwater/hydrothermal systems. Based on the distance from the craters to the steam well, the time lag between the eruptions, and the increase of 3He 4He , we estimate the magmatic component velocity in the fluid flow. The calculated value, several tens of m per day, is significantly higher than typical groundwater flow in deep sedimentary basins of Japan.

伊豆大島周辺の海底地形

Topographic features around Izu Oshima region were summarized with special references to the characteristics relating to subduction of the Philippine Sea plate (PHS) along the Sagami Trough. Several topographic highs having circular contours around Oshima Island may be the results of parasitic eruption of Oshima Volcano. Their trend is almost parallel to the elongation of the linearity of parasitic cones distributing onshore. Along the eastern trench slope off Oshima Island, large scale collapse structures are seen in the submarine topographic map. These are the result of the falling down mostly of pyroclastic materials (tephras) during historic ages. The Oshima Island shows eastward tilting owing to the bending resulted from the subduction of the PHS. Large scale of the collapse structures may be caused by the oversteepening of the eastern trench slope of Oshima Island and soft sediments consisting mostly of pyroclastics including a large quantity of pore water slide down along the trench slope as far as the Sagami Trough.Radial distribution both of saddles and valleys observed northeastern offshore part of the Oshima Island may be lava flows and/or dike swarms derived from the old Okata Volcano whose eruption center was estimated to exist at the northeastern extension of the Oshima Island.About 4 km south off the Oshima Island, large scale of the topographic breakes consisting of caotic highs and depressions are seen in the submarine topographic map. These may be debris flow deposits along eastern slope of Ohmurodashi which consists mostly of the Quaternary rhyolites geologically and chemically similar to those exposed on the Niijima and Kozushima Islands. These are the results of catastrophic phreatomagmatic eruption of the Ohmurodashi such as that of the Myojinsho. Mixture of pyroclastics and lavas will be found from these caotic areas.The upper steam of the Sagami trough shows notable meandering whose direction is almost parallel to that of the movement of the PHS east off Oshima Island and almost perpendicular east off Ohmurodashi. At the latter case, thrust structures may trace along the subduction zone at the landward slope of the Sagami trough. Just landward side of the thrust, curious round topographic highs can be observed. They may be mud volcanoes.Topographic features observed around Oshima Island may best be understood in term of the normal and oblique subduction of the Philippine Sea plate along the Sagami Trough.

Changes in cortical thickness of the clavicle and serum bone gamma-carboxyglutamic acid-containing protein in the elderly in an island community in western Japan.

The cortical thickness of the clavicle (CTC), concentrations of bone gamma-carboxyglutamic acid-containing (Gla) protein (s-BGP, osteocalcin), alkaline phosphatase (s-ALP), calcium (s-Ca) and inorganic phosphorus (s-P) in serum, and calcium/creatinine (u-Ca/Cr) and inorganic phosphorus/creatinine (u-P/Cr) ratios in urine were examined in 211 subjects aged over 40 years in Oshima Island in Nagasaki prefecture. CTC decreased and s-BGP increased with age in both sexes, especially in women. Serum BGP was significantly higher in women than in men at the ages of 50's and over. Serum ALP in women increased until the ages of 60's. Serum Ca at the ages of 50's and s-P at the ages of 60's and over were higher in women than in men. As the increase in s-BGP is reported to be coincident with active bone formation, our findings do not support the view that age-related bone loss, especially in women, primarily results from decrease in bone formation.

Periodic Observations of Subsurface Water in Izu Oshima Island

Periodic Observations of Subsurface Water in Izu Oshima Island

Centrifugal forces estimated from trajectories of drifting buoys in winding paths of the Kuroshio

Radii and angular velocities in the motions of drifting buoys deployed in the Kuroshio are estimated by fitting circles to the trajectories of two drifting buoys, one with a drogue at 300 m depth and the other at 800 m depth. The buoys were deployed in the Kuroshio where it was flowing counter-clockwise around the large cold water mass south of Honshu. The same technique was applied to two drifting buoys with drogues at 300 m depth placed in the Kuroshio where it flowed clockwise around Oshima Island in Sagami Bay. The centrifugal forces were 7% and 6% as large as the Coriolis forces in the Kuroshio around the cold water mass, and they were −56% and −42% as large as the Coriolis forces in the current around the Oshima Island. The temperature gradient observed in the Oshima-West Channel suggested that the pressure gradient there was smaller due to the centrifugal force acting against the Coriolis force than the pressure gradient to be balanced with the Coriolis force.

Observations of upwelling around the Izu Peninsula, Japan: May 1982

Hydrographic observations between the Izu Peninsula and Oshima Island, Japan, in May 1982, showed upwelling around the tip of the Peninsula and possibly also in the lee of Oshima Island. The upwelling introduced water as cold as 18 ‡C with nitrate concentrations of 3ΜM to the surface. Temperature/salinity analyses indicated that the upwelled water was of Kuroshio characteristics. Slightly fresher water was advected out of Sagami Bay in a coastal counter current.

46A. Geochemical investigations of groundwater in Oshima Island.

46A. Geochemical investigations of groundwater in Oshima Island.

Evolution of Campanula punctata Lam. in the Izu Islands: Changes of Pollinators and Evolution of Breeding Systems

Abstract The pollination and breeding systems of Campanula punctata both in the Izu Islands and the mainland (Honshu) adjacent to the islands were investigated. The predominant pollinators of campanulas are: 1) Bombus diversus in Honshu, 2) Bombus ardens and halictid bees on Oshima Island, and 3) halictid bees on the islands of Niijima, Kodzushma, and Hachijo. The absence of bumble bees except B. ardens on Oshima Island, and the abundance of halictid bees represent a kind of island effect. Flowers of the campanula in the Islands were found to be smaller than those of the mainland. This might have resulted from adaptation to the small pollinators. Pollination experiments with plants grown from seeds revealed the following differences in breeding system: 1) most of the campanulas from Honshu were highly self‐incompatible (SI) and a few partially self‐compatible (SC), 2) one half of the plants from Oshima Island were more or less SC and the remaining highly SI, 3) those from Hachijo Island were SC and potentially autogamous. The breakdown of dichogamy co‐operated with self‐compatibility in the development of self‐fertilizing ability in Hachijo plants. Several possible causes for the change in the breeding system including the change in pollinators in the Islands are discussed.

イネミズゾウムシの福岡県への侵入とその後の発生状況

Invasion of the rice water weevil (Lissorhoptrus oryzophilus KUSCHEL) in Fukuoka Prefecture was first confirmed in June 1983. The occurrence was limited to only five paddy fields on the small island of "Oshima" and 9 adult weevils were collected in 15a paddy fields in the first survey. In the following year, however, the weevil spread to the whole area of the island, and the adults were observed in paddy fields as far as 1.6 km apart from the sites where they first occurred. In the same year the weevil occurred in Shingu town and Iizuka city. Shortly after transplanting was performed on May 8, overwintered adults invaded the paddy fields and started to infect rice seedlings. Adult density increased rapidly to reach a peak at the end of May, but it decreased rapidly in early June. Two-year survey on Oshima island showed that the weevil maintained a high reproductive rate in the years immediately after the initial invasion.

Bone changes and aortic calcification in aging inhabitants of mountain versus seacoast communities in the Kii Peninsula.

Bone changes and aortic calcification were compared radiographically for different age groups of the inhabitants of two communities on the Kii Peninsula at the central southern tip of the Japanese mainland, one a mountainous Shichikawa village with a traditionally restricted nutritional intake and the other a seacoast village on Oshima Island with an abundant nutritional supply. Changes in the physical properties of the bone were also assessed by resonance measurement. In the mountainous village, bone loss appeared to occur more rapidly than in the seacoast village, as indicated by a significantly higher frequency of thoracic vertebral deformity and more pronounced age-bound decrease of ulnar resonant frequency. Aortic calcification was also more frequent in Shichikawa than on Oshima Island. Such differences were more evident in women than in men. The poorer nutritional intake (especially of calcium and vitamin D) of persons living in the mountainous village (which receives less sunshine) might be responsible for the accelerated age-bound degenerative changes observed in their skeletal and vascular systems.

The Pattern of Fishing Ground Use of Longline Fishing (Haenawa) at Mukuna in the Ochi Islands

The aim of this report is to describe the pattern of fishing ground use of longline fishing at Mukuna in Oshima Island, Ehime Prefecture. To study some aspects of longline fishing the author made a field survey in the ecological point of view. The the author's method has been wanting in the field research of geography of fisheries so far. The data of this report, therefore, was obtaind by a diarect observation method in addition to hearing and collecting documents in the field.The results of the research can be summarized as follows.1) Longline fishing is operated throughout one year. The fishing season is divided into two categories by seasonality of catch; in November to April hogonawa catching mainly hogo (Sebastiscus marmoratus) is operated, while in May to October tamorinawa catching tamori (Hapalogenys mucronatus) and anago (Astroconger myriaster) is operated.2) Feeding habit of fish limits the time of the longline fishing operation. The hogo is diurnal, while the tamori and the anago are nocturnal. Hogonawa, therefore, is operated in the daytime, while tamorinawa is carried out early in the morning and the nighttime.3) The longline fishing must be operated in time-zone, called toromi, in which tidal movement changes from ebbing to flowing and from flowing to ebbing.4) There are 21 fishing grounds of longline fishing around Mukuna. They are divided into four categories by toromi.a. fishing grounds usable at toromi of ebb tideb. fishing grounds usable at toromi of flow tidec. fishing grounds usable at both toromi of ebb and flow tided. fishing ground not having relation to toromi5) Each fisherman in general uses only 1 to 5 fishing grounds where he is very familiar with conditions of tide, sea bottom, and so on.6) The activity of longline fishing is divided into three categories: (a) preparing for going out fishing at the port, (b) operating at the sea, and (c) landing catch and taking care of fishing gears at the port. The total time necessary for activity of (a), (b), and (c) is about 600 to 700 minutes. Therefore it is impossible for the fisherman to operate more than two times a day.

An Estimation of Age and Life-Span of the Genus Trimeresurus (Reptilia, Serpentes, Viperidae) on Amami Oshima Island, Japan

Two species of snakes of the genus Trimeresurus, Trimeresurus flavoviridis and Trimeresurus okinavensis, inhabit Amami Oshima Island in the Loo-Choo Islands. These are the common terrestrial venomous snakes on Amami Oshima Island. There is a ring structure on the centra of vertebrae in these snakes. I tried to confirm by in vivo staining that rings on centra were formed annually. Then, age and life-span was estimated by Walford's graphic method. It appears that the age of these snakes can be estimated by adding total ring number +1. The life-span of

3P. Submarine volcanoes between Izu Peninsula and Oshima Island(Abstracts of Papers Submitted for the Meeting of the Society)

3P. Submarine volcanoes between Izu Peninsula and Oshima Island(Abstracts of Papers Submitted for the Meeting of the Society)

4P. The structure of Oshima Island as inferred from magnetization intensity(Abstracts of Papers Submitted for the Meeting of the Society)

4P. The structure of Oshima Island as inferred from magnetization intensity(Abstracts of Papers Submitted for the Meeting of the Society)

On the surface gleyed red and yellow soils on the Amami Oshima Island

On the surface gleyed red and yellow soils on the Amami Oshima Island

新島および大島におけるくさや汁の微生物相

The microbial flora of the kusaya brine was studied in samples obtained from manufacturers in Niijima and Oshima Islands. The classification of bacteria at the genus level was performed on 144 strains from Niijima Island and 107 strains from Oshima Island. No significant difference in the bacterial flora was observed between these brines, though molds were isolated only from Niijima samples. Bacteria of genus Corynebacterium (about 56% of total isolates) which formed minute colonies on nutrient agar plate were the most predominant in the brine followed by bacteria of genus Pseudomonas (about 22-37% of total isolates). As the characteristic organisms in the brine, bacteria of genus Spirillum were isolated from all samples in small numbers.

28. Submarine volcanoes between Izu Peninsula and Oshima Island.(Abstracts of Papers Submitted for the Meeting of the Society)

28. Submarine volcanoes between Izu Peninsula and Oshima Island.(Abstracts of Papers Submitted for the Meeting of the Society)