魚類学雑誌
Online ISSN : 1884-7374
Print ISSN : 0021-5090
ISSN-L : 0021-5090
沖縄島沿岸域におけるグルクマの成熟様式と初期生活史
上原 匡人本永 文彦太田 格海老沢 明彦宮岡 勇輝立原 一憲
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ジャーナル 認証あり 早期公開

論文ID: 20-037

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The Indian mackerel Rastrelliger kanagurta is an important coastal fishery resource for Okinawa Prefecture, southwestern Japan. However, much is still unknown about its life history. The early development, occurrence, sexual maturation, and reproductive cycle of the species was examined from specimens collected from the coastal waters of Okinawa Island, and management of the fishery evaluated. Larvae [3.4 mm notochord length–12.5 mm standard length (SL)] and juveniles (11.4–16.2 mm SL) of R. kanagurta were distinguished from other mackerel species by: 1) numbers of myomeres, 2) absence of spines on the preopercle posterior margins, 3) positional relationship between the upper and lower jaw tips, 4) melanophore pattern, and 5) distribution (allopatric). Both larvae and juveniles occurred in the offshore epipelagic zone of Nakagusuku Bay in May, June, and August, which coincided with the occurrence of high-gonadosomatic value adults in coastal waters. However, specimens were not encountered in extremely shallow coastal areas (e.g., tidal flats), although younger individuals may utilize such the offshore epipelagic zone of the bay, attaining fork lengths (FL) of ca. 8 cm. Individuals mature at ca. 26 cm FL, one year after hatching. R. kanagurta are primarily caught by set net fishery near Okinawa, small (immature) individuals accounting for > 45% of netted individuals in all months, except May and June, during the period from April 1985 to April 1987, and for > 35% of the examined individuals in all months, except June and July, between April 2011 and March 2016. These results for both periods suggest growth overfishing. Accordingly, immature individuals must be conserved to sustain the Okinawan population of R. kanagurta.

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© 2021 The Ichthyological Society of Japan
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