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潮境域におけるカツオ回遊魚群の行動生態および生理に関する研究
https://fra.repo.nii.ac.jp/records/2007424
https://fra.repo.nii.ac.jp/records/2007424ce417058-d081-4114-9f44-8b527d40cba8
| Item type | 紀要論文 / Departmental Bulletin Paper(1) | |||||||||||
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| 公開日 | 2024-06-10 | |||||||||||
| タイトル | ||||||||||||
| タイトル | 潮境域におけるカツオ回遊魚群の行動生態および生理に関する研究 | |||||||||||
| 言語 | ja | |||||||||||
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| 言語 | jpn | |||||||||||
| 資源タイプ | ||||||||||||
| 資源タイプ識別子 | http://purl.org/coar/resource_type/c_6501 | |||||||||||
| 資源タイプ | departmental bulletin paper | |||||||||||
| アクセス権 | ||||||||||||
| アクセス権 | metadata only access | |||||||||||
| アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||||||||
| 著者 |
二平, 章
× 二平, 章
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| 抄録 | ||||||||||||
| 内容記述タイプ | Abstract | |||||||||||
| 内容記述 | Frontal areas are one of the most important fishing grounds for migratory fishes. There have been many reports on the relationship between oceanographic features of fronts and the distributions of migratory fishes. However, most of these reports have just described the apparent relationship between them and not investigated the behavioral and physiological aspects essential to understand the mechanism behind this relationship. Studies on these aspects will contribute to clarify the interactions between the expansions and contractions of migratory areas and fluctuations in population sizes. A clearer understanding is also essential to forecast fishing ground locations and available stock abundances. This study aims to clarify the behavior and the thermal physiology of the skipjack tuna Katsuwonus pelamis which migrates to the frontal area off the northeastern coast of Japan.Results are summarized as follows :1. Biological characteristics of skipjack tuna migrating to the frontal area off the northeastern coast of Japan. Biological characteristics such as the fork length, gonad index, condition factor, condition factor except internal organs, liver index and index of fat deposition of the stomach of skipjack tuna were investigated during 1971-1993 to clarify the stock structure and the mechanism of the formation of the fishing ground around the oceanic front. Recovered data from skipjack tunas tagged and released in the Kuroshio-Oyashio transitional area in autumn during 1978-1992 were used to detail their northward and southward migrations. 1) Five size groups (A~E) are identified among skipjack tunas migrating to the area off the northeastern coast of Japan. The size group, "A" 51~54 cm mean fork length, migrates to this area in April. The size groups "B" and "C" appear from May to June, mean fork lengths vary from 45 ~48 cm for group "B" and 42~44 cm for group "C". The size groups "D" and "E" appear after August, with a mean fork length varying from 41-45 cm and below 40 cm respectively. Results of tagging experiments indicate that the "E" group which appears in autumn, increases in size to become the "C" group in the following year and further to the "A" group after two years, while the "D" group becomes the "B" group in the following year. It is also suggested that the "E" group is spawned in the area between the North Equatorial Current to the Equatorial Current during winter, and that the "D" group is spawned in the area of the Subtropical Counter Current in summer. 2) Fish belonging to the "A" group and some of the "B" group seem to mature in spring because their sizes exceed the minimum size of maturation, 45 cm fork length. For this reason, after migrating to the southern edge of the Kuroshio Extension, they migrate back to subtropical area for spawning. 3) Only immature fish belonging to the "B" and "C" groups migrate northward and pass through the Kuroshio Front. Biological indices (fork length, condition factor, condition factor except internal organs, liver index and index of fat deposition on the stomach) are higher for individuals collected in the northern area than those collected in the southern area of the Kuroshio Front. 4) After the northward migration for feeding, the "B" and "C" groups begin to migrate southward in autumn and remain in the tropical area to overwinter. On the other hand, the "D" and "E" groups spend the winter in the Kuroshio area. 2. Behavior of skipjack tunas tagged in the frontal area Tagged skipjack tunas were released at a secondary Kuroshio Front in August, 1981 and at the Kuroshio Front in May and June, 1986 to investigate the relationship between the oceanographic features of these areas and the biological conditions of fish migrating northward. 1) Skipjack tunas migrating to the Kuroshio Extension area in spring, before arriving at the southern edge of the warm core, decide whether they turn back to the subtropical area or continue their migration northward. All of the fish which migrates to the Kuroshio Front passes through the front and enters into the Kuroshio-Oyashio transitional area. 2) In June, when the surface water temperature of the warm streamers is lower than 20℃, only large size skipjack tunas, above 45 cm in fork length, are able to migrate northward by this route. 3) In September, large size skipjack tunas pass through the secondary Kuroshio Front and enter into the cold water area with an increase in their condition factor. However, small size skipjack tunas turn back from the front to the warm water area. The phenomenon by which large and small size fish are separated at the oceanic front is termed "size-screening" hereafter. 3. Distribution of skipjack tunas caught by floating gill nets in the Kuroshio Front Distributions of skipjack tunas in the Kuroshio area and warm streamers were investigated using floating gill nets in June during 1987-1988. 1) Both large and small size skipjack tunas inhabit in the southern area of the Kuroshio Front, while only large size fish were collected in the northern area of the front in 1987. "Size-screening" was clearly recognized at the front. 2) Skipjack tunas sampled at the front of the western edge of a warm streamer, 20.4˚C surface water temperature, mainly fed on Euphausiacea and larval anchovy. On the other hand, skipjack tunas caught in the colder water side of the front, 18.3˚C the surface water, mainly fed on Euphausiacea and sardine. The weight of the stomach contents of skipjack tunas caught near the front of the warm streamer was twice to five times higher than those caught at the center of the warm streamer. From this, the frontal area seems to be the most suitable feeding place for the skipjack tunas. 4. Behavior of skipjack tunas in the frontal area from a thermal ecological point of view. Fat content and body temperature of skipjack tunas in the western Pacific Ocean from the tropical area to the Kuroshio-Oyashio transitional area were investigated. 1) The fat contents of skipjack tunas increase when they pass through the Kuroshio Front and enter into the transitional area in spring. The fat contents also increase when they enter into the warm streamer protruding into the Oyashio water from the secondary Kuroshio Front in autumn. Fat is accumulated under the skin and around the stomach. Large size skipjack tunas, over 45 cm in fork length, accumulate more fat than smaller ones. The fat accumulation seems to contribute to the maintenance of the high body temperature when they enter into colder water. 2) When skipjack tunas of 30~55 cm in fork length migrate to the transitional area, they maintain their body temperature above 22˚C in spite of the drop in the ambient water temperature. Since skipjack tunas below 45 cm in fork length can not continuously maintain their body temperature over 22˚C in ambient water temperature below 20˚C, they decrease their metabolic rate and can not sufficiently feed and accumulate fat. This seems to be the main cause of the "size-screening" at the front. 3) During the southward migration period, large size skipjack tunas raise their body temperature in the transitional area and smoothly pass through the Kuroshio Front southward, and migrate to the southern area of the Subtropical Counter Current, where the ambient water temperature is 26 ~27˚C. On the other hand, since small size skipjack tunas, below 42~43 cm in fork length, can not raise their body temperature like the larger size fish, they can not migrate southward over long distances and tend to remain within the Kuroshio area even in winter. 5. Conclusions Putting together the above results on the ecological and physiological characteristics of skipjack tunas sampled from in and adjacent areas to the frontal area of the Kuroshio Extension, the following are concluded : 1) In the Kuroshio Front and the transitional area, fish below 45 cm in fork length can not maintain their body temperature above 22˚C, which may be the lowest limit of body temperature for skipjack tuna. Therefore, they stay in waters with temperature above 20˚C. On the other hand, fish above 45 cm in fork length are able to accumulate fat under the skin and around the stomach which helps avoid excessive cooling, thus they can pass through the front and enter into the cold waters of the transitional area. This could be a possible mechanism for the "size-screening" at the front. 2) Skipjack tunas passing through the Kuroshio Front migrate further north into the warm streamer protruding into the Oyashio area, and succeed in exploiting the abundant food available. This makes it possible for them to accumulate much fat and to migrate southward over long distances to the tropical area for spawning. 3) Possible mechanisms for fishing ground formation based on these characteristics are proposed. Skipjack tunas which are maturing during the period of their northward migration in the Kuroshio area in spring, turn back from the southern edge of the Kuroshio Extension to the subtropical area. Therefore, only immature skipjack tunas pass through there and migrate to the Kuroshio Front. In large stock size years, as the result of relatively slow growth of the skipjack tunas due to density effects, the rate of immature and small size individuals with low condition factors increases during the northward migration period. This subsequently decreases the quantity of fish which turns back from the southern edge of the Kuroshio Extension and promotes the aggregation of the northward migration fish with a low condition factor which can not immediately enter into the warm streamer by "size-screening" effects at the Kuroshio frontal fishing grounds. In small stock size years, on the other hand, the opposite situation occurs and the fish aggregation is less favorable at the Kuroshio frontal fishing grounds, leading to a large scale turn back from the southern edge of the Kuroshio Extension to the subtropical area and consequently to poor fisheries at the Kuroshio Front. | |||||||||||
| 言語 | en | |||||||||||
| 抄録 | ||||||||||||
| 内容記述タイプ | Abstract | |||||||||||
| 内容記述 | 潮境域は陸棚や湧昇域とともに回遊性浮魚類の重要漁場であり,これまでにも多くの研究がなされてきた.しかし,潮境の海洋構造と漁場の位置関係を示す事実記載的な研究がそのほとんどであり,魚群の行動生態学的あるいは生理生態学的な研究は皆無に近い。魚群の回遊行動や資源量変動に伴う回遊域の拡大·縮小の機構などの問題を,生物と環境の相互作用の面から解明し,また,これらの生態学的な知見を基礎とした漁場形成や漁況の予測手法を改良するためにも,魚群の回遊行動に対する生理生態学的な研究が必要である.本研究は,東北近海の潮境域に来遊するカツオ Katsuwonus pelamis を対象として,主に標識放流と流し刺網調査および体温測定により,その回遊行動と生理および潮境環境との関連性を明らかにした.研究成果の大要は以下のとおりである.1. 日本近海に来遊するカツオの生物学的特性 茨城県那珂湊港における1971~1993年の体長測定データをもとに,カツオの資源構造,生物特性値(生殖腺指数,肥満度,内臟除去肥満度,肝臟重量指数,腸間膜脂肪量指数)の変化と潮境の位置関係を解析するとともに,標識放流調査によりカツオの回遊生態を検討した.その結果,以下のことが明らかになった.1) 春·夏季に東北近海域に来遊するカツオには,来遊の時期と体長により冬季発生する群と夏季発生する群に由来するA~Eの5つの群が存在する.A群は4月に出現し,その時の平均体長は51~54 cm,B·C群は5~6月に出現し,前者は45~48 cm,後者は42~44cm,D·E群は8月以降に出現し,前者は41~45cm,後者は30cm台の大きさである.北赤道海流域から赤道海流域で冬に生まれるE群は成長して翌年C群に,さらにその翌年の春A群になる.他方,主に亜熱帯反流域で夏に生まれるD群は翌年の春B群となる.2) カツオは体長45.0cm付近から成熟度を増加させることから,B群の一部とA群は春季に成熟過程に入る.そのため,これらの魚群は黒潮続流の南縁付近まで北上した後,Uターンして南下し産卵群となる.3) B群の一部とC群のほとんどは,黒潮前線を越えて北上する.北上するB·C群は未成熟個体のみである.また,それらの体長,肥満度,内臓除去肥満度,肝臓重量指数,腸間膜脂肪重量指数はいずれも黒潮前線を境に北側で不連続的に高くなる.4) 北上したB·C群は秋·冬季に亜熱帯反流域および赤道海域まで南下するが,D·E群は南下しても黒潮周辺域どまりである.2. 標識放流調査からみた潮境域におけるカツオの行動生態 潮境における魚群の行動調査のため,1981年8月に2次黒潮前線,1986年5,6月に黒潮続流の前線付近でカツオを標識放流し,放流時と再捕獲時の生物特性値を比較検討した.その結果,以下のことが明らかになった.1) 春季に黒潮続流水域まで北上してきたカツオ魚群のUターン行動の決定は黒潮続流の最高水温帯の南縁付近で行われる.北縁の黒潮前線まで北上した個体は最終的にはすべて北上する.2) 6月に黒潮前線から北にのびる暖水ストリーマに乗って北上する個体は,ストリーマの水温が約20℃以上になるまでは体長·肥満度の大きいものに限られる.3) 9月に2次黒潮前線付近まで北上した群のうち,体長45cm以上の大型魚は潮境を通過し肥満度を高めながら北の低水温域側へ侵入するが,小型魚は潮境から高水温帯側に戻る.潮境域におけるこの体サイズ別の魚群のふるい分け現象を「サイズスクリーニング」と呼ぶことにした.3. 流し刺網調査からみた潮境域におけるカツオの分布と海洋環境 潮境域におけるカツオ魚群の分布と海洋構造の関係を調べるために,1987年と1988年の6月に黒潮水域および暖水ストリーマ内において流し刺網調査と海洋調査を実施し,以下のことを明らかにした.1) 黒潮前線南の暖水域では体長45cm以下と45cm 以上の個体が混在するのに対して,北の冷水側では体長45cm以上の大型魚のみが分布し,サイズスクリーニング現象が認められる.2) 暖水ストリーマ西縁部のフロント付近(表面水温20.4℃)におけるカツオはオキアミ類とカタクチシラス,低水温側(表面水温18.3℃)に分布したカツオはオキアミ類とマイワシを主に食べていた,ストリーマ内のカツオのうち,先端部付近の個体の胃内容物重量は中央部付近の個体の2~5倍もあり,より活発に採餌していることがわかった.4. 温度生態学的視点からみた潮境域におけるカツオの行動 黒潮と親潮の間の混乱水域に分布するカツオの部位別蓄積脂肪量の測定と,北西部太平洋全域のカツオの体温測定により,以下のことを明らかにした.1) カツオの脂肪蓄積量は,春季に魚群が黒潮前線を越えて混乱水域に北上した時と,秋季に暖水ストリーマ北縁の低水温域に侵入した時に増加する.体長45 cm以上の大型個体は小型個体に比べて蓄積脂肪量が高い.この脂肪は主に皮下部と胃腸壁部に蓄積されており,低水温環境域に侵入するカツオの体温保持に有効であると考えられる.2) 混乱水域に来遊する体長30~55cmのカツオは,環境水温が低下しても,代謝のための最低体温22℃を保つ.体長45cm以下の小型個体は,断熱層としての脂肪蓄積量が少ないため,大型個体に比較して体温を高く保つ能力が劣るので,水温環境が20℃以下になると代謝活性が低下すると考えられる.このことが潮境におけるサイズスクリーニング現象の基本的な要因であると推察される.3) 南下期のカツオのうち,大型個体は潮境通過前に体温を上昇させ,水温26~27℃の亜熱帯反流以南の水域まで一気に南下する.一方,体温が大型個体ほど高くならない体長42~43cm以下の小型個体は,南下しても黒潮周辺域にとどまる傾向がある.以上により,黒潮続流の潮境域におけるカツオ魚群の回遊に関わる生理生態学的特性と漁場形成の経年変動の機構に関して,以下のことが結論される.(1) 黒潮続流の南縁ですでに成熟過程に入った魚群は南にUターンする.肥満度が高い魚群の一部は前線を越えて混乱水域に入るが,南側にUターンする個体の割合は肥満度の低い魚群に比べて高い。(2) 混乱水域に来遊する魚群のうち,体長30~45cm の個体は20℃以下の水温環境下では体温を高く保持する機構がないために,20℃以上の暖水域にとどまる.一方,体長45cm以上の索餌群は,皮下部に脂肪を蓄積することにより体温保持機構を備え,潮境を越えて低水温域まで侵入する.その結果,サイズスクリーニング現象が生じる.(3) 北に侵入した大型個体は親潮水域表層部に伸びる暖水ストリーマを利用してその先端付近まで侵入し,多量の栄養蓄積を行うことにより,亜熱帯反流以南の産卵域までの長距離南下回遊を可能にする.(4) 資源量の水準が高い年は個体の成長と発育が遅れ,未成熟·低肥満度·小型魚の出現割合が増え,黒潮南縁域でUターンせずに北上する魚群量が増加する.さらに,前線付近でサイズスクリーニング現象のために滞留する魚群の量が増える結果,黒潮続流域の前線漁場形成は活発となる,資源の低水準年には逆の現象が生じ,前線漁場の形成は不活発となる. | |||||||||||
| 言語 | ja | |||||||||||
| 書誌情報 |
ja : 東北区水産研究所研究報告 en : Bulletin of Tohoku National Fisheries Researh Institute 巻 58, p. 137-233, ページ数 97, 発行日 1996-03-31 |
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| 出版者 | ||||||||||||
| 出版者 | 東北区水産研究所 | |||||||||||
| 言語 | ja | |||||||||||
| 出版者 | ||||||||||||
| 出版者 | Tohoku National Fisheries Researh Institute | |||||||||||
| 言語 | en | |||||||||||
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| 収録物識別子タイプ | PISSN | |||||||||||
| 収録物識別子 | 0049-402X | |||||||||||
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| 収録物識別子タイプ | NCID | |||||||||||
| 収録物識別子 | AN00167637 | |||||||||||
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| 識別子タイプ | Local | |||||||||||
| 関連識別子 | tnf_k_58_137 | |||||||||||
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| 識別子タイプ | URI | |||||||||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010541827 | |||||||||||
| 言語 | ja | |||||||||||
| 関連名称 | 日本農学文献記事索引(agriknowledge) | |||||||||||
