Stock assessment and release strategy of red sea bream Pagrus major in Kagoshima Bay, Japan (original) (raw)
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Japanese Journal of Limnology (Rikusuigaku Zasshi)
The Ogasawara mitten crab Eriocheir ogasawaraensis is a varunid species endemic to the Ogasawara (Bonin) Islands. Although this crab undertakes catadromous migration to the sea for reproduction, little is known about its ecological characteristics. Therefore, we carried out field surveys on the distribution patterns of E. ogasawaraensis and other brachyuran crabs in the rivers and streams of Chichi-jima, Ogasawara Islands, from June to July and in November, 2007. Although, the streams and rivers of Chichi-jima are generally small and the range of the tidal river area is usually very short, the upper tidal river area is an extremely important habitat for the recruitment and maintenance of the mitten crab population. The present survey revealed that E. ogasawaraensis settled in a narrowly limited area nearly dozens of meters long at the rivermouth. Juvenile crabs (13-23 mm carapace width) with relatively longer legs migrated upstream to the headwaters at a high altitude. Though the distribution of E. ogasawaraensis covered the entire river area, it was strongly inclined toward the headwaters. The microhabitat of the crab was usually underwater, though an occasional adult crab wandering along the riverside wetland was also captured. This distribution pattern differs from that of its congener, E. japonica, which favors freshwater downstream areas in mainland Japan. In addition, the number of mitten crabs caught was too small for the effort made in the present survey, suggesting that the population of this species in Chichi-jima may be endangered. Three brachyuran species (Ptychognathus glaber, Varuna litterata and Chiromantes dehaani) were also widely distributed from the downstream area to the upper freshwater area in the river. Complexity of brachyuran species composition in the rivers and streams of Ogasawara Islands was generally poor compared to that in the Japanese mainland and the Ryukyu Islands.
Japanese Journal of Ornithology, 2006
The Great Cormorant Phalacrocorax carbo is generally considered to be a major predator of Sweetfish Plecoglossus altivelis released primarily for recreational fishing. We counted Great Cormorants, herons and anglers along 400 km of rivers and at seven lakes in or close to Tochigi Prefecture at the end of May, June and August 2005. We recorded a total of 433 Great Cormorants, 516 herons of four species, and 736 anglers. Along rivers suitable for Sweetfish angling, Great Cormorants were fewer than at other sites and fewer than Grey Herons Ardea cinerea, Great Egrets Egretta alba, or anglers.
2011
阿蘇海は宮津湾の西部の湾入部が堆砂によって仕切られた海跡湖である。その阿蘇海内に形成されたカキ礁内部に生息するアマオブネガイ目の巻貝ミヤコドリ（Phenacolepas pulchella）を採集した。海跡湖に生息するカキ礁を生息環境とするミヤコドリの報告は初めてである。採集したミヤコドリの殻表面は黒色沈着物で覆われていた。この黒色沈着物について，電子プローブマイクロアナライザー（EPMA）を用いて電子像による形態観察，定性分析および定量分析を行ったところ，顕著なマンガン（Mn）のピークが検出され，沈着物の主成分は酸化マンガン（MnOn）であることが示された。これまでミヤコドリの殻表上の付着物は還元鉄が付着して茶色になる（土屋，2000）とされていたが，分析の結果，阿蘇海で採集されたミヤコドリの殻表面には酸化マンガンが濃集していることがわかった。阿蘇海のミヤコドリ生息域における酸化還元条件が，酸化還元に敏感な元素であるマンガン（Mn）の沈着に深く関与している可能性が考えられる。Aso-kai is a lagoon separated by sand spit from the Miyazu Bay, a marginal water of the Sea of Japan. We collected individuals of Phenacolepas pulchella, belonging to the order Neritimorpha, from inside of oyster reefs, as the first record of such inhabitation. Shell surface of P. pulchella accumulated blackish deposits. Electron probe micro-analysis revealed that the deposits consist mainly of manganese oxides (MnOn). Geochemical setting of the habitat may facilitate accumulation of the redox-sensitive element, Mn