著者

上原 匡人 本永 文彦 太田 格 海老沢 明彦 宮岡 勇輝 立原 一憲

出版者

一般社団法人 日本魚類学会

雑誌

魚類学雑誌 (ISSN:00215090)

巻号頁・発行日

vol.68, no.2, pp.129-142, 2021

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<p>The Indian mackerel <i>Rastrelliger kanagurta</i> 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 <i>R. kanagurta</i> 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. <i>R. kanagurta</i> 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 <i>R. kanagurta</i>.</p>

著者

上原 匡人 太田 格 海老沢 明彦 立原 一憲

出版者

一般社団法人 日本魚類学会

雑誌

魚類学雑誌 (ISSN:00215090)

巻号頁・発行日

vol.68, no.2, pp.93-107, 2021

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<p>Two closely related, commercially important threadfin breams, <i>Nemipterus furcosus</i> and <i>N. peronii</i>, are an essential coastal fishery resource in Okinawa Prefecture. The age, growth, reproductive cycle, and stomach contents from 124 <i>N. furcosus</i> and 37 <i>N. peronii</i>, obtained from November 2011 to December 2015, were examined, age being assessed from sectioned otoliths and gonadal histology. <i>Nemipterus furcosus</i> and <i>N. peronii</i> were the most abundant threadfin breams in Kin Bay and Nakagusuku Bay, Okinawa Island, areas including many coastal tidal flats, where the two species comprised 98.1% of the total number of <i>Nemipterus</i> individuals examined. Overall sex ratios of both species were significantly sex-biased, the apparent lack of transitional gonads implying functional gonochorism. The spawning seasons of both species were estimated as occurring between spring and fall, no immature fishes having been obtained. Age validation using edge-type analyses implied that opaque zones were formed once per year, being valid annual growth increments. Although no intersex differences in maximum length, growth equation, and age range were observed in <i>N. furcosus</i>, <i>N. peronii</i> females were larger and older than males. The greatest ages observed were 4.3 and 7.0 years for <i>N. furcosus</i> and <i>N. peronii</i>, respectively. Both species fed predominantly on crabs, which primarily occupied the inner bays. Over the previous 27 years, the catch per unit effort of <i>Nemipterus</i> has declined in the highly altered environments of Kin and Nakagusuku Bays, suggesting that the decline in the populations of these species at Okinawa Island may be due to coastal fishery practices, environmental decline, and the degradation of suitable habitats. The biological implications for conservation are discussed.</p>

著者

上原 匡人 本永 文彦 太田 格 海老沢 明彦 宮岡 勇輝 立原 一憲

出版者

一般社団法人 日本魚類学会

雑誌

魚類学雑誌 (ISSN:00215090)

巻号頁・発行日

2021

---

<p>The Indian mackerel <i>Rastrelliger kanagurta</i> 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 <i>R. kanagurta</i> 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. <i>R. kanagurta</i> 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 <i>R. kanagurta</i>.</p>

著者

上原 匡人 太田 格 海老沢 明彦 立原 一憲

出版者

一般社団法人 日本魚類学会

雑誌

魚類学雑誌 (ISSN:00215090)

巻号頁・発行日

2021

---

<p>Two closely related, commercially important threadfin breams, <i>Nemipterus furcosus</i> and <i>N. peronii</i>, are an essential coastal fishery resource in Okinawa Prefecture. The age, growth, reproductive cycle, and stomach contents from 124 <i>N. furcosus</i> and 37 <i>N. peronii</i>, obtained from November 2011 to December 2015, were examined, age being assessed from sectioned otoliths and gonadal histology. <i>Nemipterus furcosus</i> and <i>N. peronii</i> were the most abundant threadfin breams in Kin Bay and Nakagusuku Bay, Okinawa Island, areas including many coastal tidal flats, where the two species comprised 98.1% of the total number of <i>Nemipterus</i> individuals examined. Overall sex ratios of both species were significantly sex-biased, the apparent lack of transitional gonads implying functional gonochorism. The spawning seasons of both species were estimated as occurring between spring and fall, no immature fishes having been obtained. Age validation using edge-type analyses implied that opaque zones were formed once per year, being valid annual growth increments. Although no intersex differences in maximum length, growth equation, and age range were observed in <i>N. furcosus</i>, <i>N. peronii</i> females were larger and older than males. The greatest ages observed were 4.3 and 7.0 years for <i>N. furcosus</i> and <i>N. peronii</i>, respectively. Both species fed predominantly on crabs, which primarily occupied the inner bays. Over the previous 27 years, the catch per unit effort of <i>Nemipterus</i> has declined in the highly altered environments of Kin and Nakagusuku Bays, suggesting that the decline in the populations of these species at Okinawa Island may be due to coastal fishery practices, environmental decline, and the degradation of suitable habitats. The biological implications for conservation are discussed.</p>