Bulletin of the Hiroshima University Museum Issue 10
2018-12-25 発行

瀬戸内海三原瀬戸におけるイカナゴの夏眠底質環境

Estivation grounds of the sand lance Ammodytes japonicus (Ammoditidae) in the Mihara Strait, mid-western Seto Inland Sea, Japan
Endo, Azusa
Iwasaki, Nami
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abstract
The sand lance Ammodytes japonicus in the Seto Inland Sea is known to estivate in fine sandy grounds when water temperatures reach above 19ºC, usually from late June to early December. Catches of the sand lance have decreased drastically since the mid-1980s, coinciding with large-scale quarrying for bottom sands, which strongly suggests that sand lance populations have been seriously impacted as a result of deterioration and disturbances to sandy-bottom habitats. Mihara Strait was once a major fishing ground for sand lance and has also suffered from quarrying. To evaluate the present condition of the sandy areas of Mihara Strait as potential estivation grounds of the sand lance, we sampled sediments at 11 survey points, using a square-shaped dredge towed by the training vessel Toyoshio-maru of Hiroshima University, in 2014 and 2015. We then analyzed the physical characteristics of the sediment samples. Sand lance individuals were observed in the sediments collected from five survey points: three on the western side and two on the eastern side of the strait. Sediments at these five survey points comprised sandy elements of 0.25–4.0 mm diameter, which constituted over 80% of the weight ratio of the sediment samples. Sediments from the other survey points included pebble elements and had significantly lower weight ratios of sandy elements, suggesting the unsuitability of the substrate at those points for burrowing by the sand lance. Thus, it is suggested that sandy grounds for estivation of the sand lance are geographically limited in Mihara Strait at present, a situation that may restrict population recovery of this species in these waters.
description
本研究は,環境省環境研究総合推進費S-13「持続可能な沿岸海域実現を目指した沿岸海域管理手法の開発(2014-2018年度;代表 柳 哲雄)」の助成を受け,サブテーマ「閉鎖性海域・瀬戸内海における栄養塩濃度管理法の開発(テーマリーダー 西嶋 渉)」のプロジェクト事業の一環として実施したものである。
subject
イカナゴ
夏眠
三原瀬戸
粒度組成
せん断強度
sand lance
estivation grounds
Mihara Strait
sediment components
vane share strength
rights
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