Journal of the Graduate School of Biosphere Science, Hiroshima University Volume 52
2013-12-25 発行

広島湾江田島沖のカキ養殖筏の垂下構造中にみられた魚類

A list of fishes found on the oyster farming rafts by the underwater visual census in northern Hiroshima Bay, Seto Inland Sea, Japan
file
abstract
The oyster farming rafts occupy 200ha of the water surface in Hiroshima Bay. Each floating raft (ca.11m wide x 26m long) hangs a total of 600 wires (ca. 10m depth) each attaching 40 oysters’ collectors, providing a complex underwater structure. Though the raft structure has been suggested to provide nursery habitats for fishes, information of fishes found around the oyster raft has been very limited hitherto. In order to obtain data of the species composition and the abundance of fishes occurring on the raft structure, we conducted visual census at off Eta-shima Island, northern Hiroshima Bay, during the daytime on August 5 and October 3, 2011. The collecters were dropped in 0-15m depth from floating rafts. Five observers swam for 52m along the outer edge of the raft in 5-9m depth, with recording fish species and individual numbers occurring within the structure (ca. 100min observation for each raft). The underwater survey was conducted for two types of the rafts in each survey month; a raft with well-grown oysters after overwintering (called the late raft) and one with oyster spats (called the early raft). A total of 24 fish species (16 families) were confirmed and almost of them (23 species) have ever been known as occurring on rocky reefs in Hiroshima Bay. Four fishes, a sparid Acanthopagrus schlegelii, a gobiid Tridentiger trigonocephalus, monacanthids Rudarius ercodes and Stephanolepis cirrhifer, commonly occurred in all four surveyed rafts, suggesting their high abilities in fitting for the environmental conditions of the oyster rafts. The late rafts maintained significantly higher values both in mean fish species numbers and in mean fish abundance than the early rafts, implying that the environmental conditions would become attractive for fishes as a nursery habitat in accordance with the growth of oysters mooring for longer periods.
description
本研究は平成23年度広島大学地域連携推進研究事業の支援を受け,プロジェクト「魚類によるカキならびにアサリの食害防除に関する生物学的研究」の一環として実施したものである。
subject
出現魚種数
出現個体数
潜水センサス
広島湾
マガキ筏式垂下養殖
abundance
fishes
Hiroshima Bay
oyster raft
species composition
underwater census