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西部北太平洋熱帯域におけるカツオの初期生態に関する研究
https://fra.repo.nii.ac.jp/records/2010775
https://fra.repo.nii.ac.jp/records/20107750c4bc76b-e7fb-472a-a649-7e20fae0fa7e
| 名前 / ファイル | ライセンス | アクション |
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fra_k_3_63.pdf (721.6 KB)
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| Item type | 紀要論文 / Departmental Bulletin Paper(1) | |||||
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| 公開日 | 2024-10-02 | |||||
| タイトル | ||||||
| タイトル | 西部北太平洋熱帯域におけるカツオの初期生態に関する研究 | |||||
| 言語 | ja | |||||
| タイトル | ||||||
| タイトル | Studies on the early life ecology of skipjack tuna, Katsuwonus pelamis, in the tropical western-north Pacific. | |||||
| 言語 | en | |||||
| 言語 | ||||||
| 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 | open access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_abf2 | |||||
| 著者 |
田邉, 智唯
× 田邉, 智唯 |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | The objective of this study is to provide new information on the early life ecology of skipjack tuna. It is necessary to clarify the recruitment process of the skipjack tuna population and to establish a basis for stock management in the western Pacific. In order to collect large number of juvenile skipjack tuna, a new sampling protocol and associated gear were developed. The midwater trawl net TANSYU had a estimated mouth opening of 20m×20m, 72m total length, 1000-57mm mesh size at the body, 8 mm mesh size at the codend, and 5 knots maximum towing speed. A total of 497 tows was conducted in the tropical western Pacific (0-20˚N, 130-160˚E), from October to December during the years 1992-1996, resulting in the collection of 6724 skipjack, 6-172 mm tandard length (SL), and 0-1163 individuals (inds)/1 hr tow. These results indicate the establishment of a new sampling method for capturing much larger numbers of juvenile skipjack tuna than was possible using the sampling gear of previous studies. In addition, samples of 1373 other tunas, 8-140 mm SL, 0-128 inds/ 1 hr tow, were collected. These results verify that the TANSYU is an effective sampling gear for juveniles of not only skipjack tuna but also of other tunas and large oceanic fishes. Juvenile skipjack tuna are widely distributed in the north equatorial current area (NEC), the north equatorial counter current area (NECC), and the boundary area of these two currents. Vertically, juvenile skipjack tuna appeared mainly from the lower portion of the mixed layer to the upper portion of the thermocline. The abundance indices, frequency of occurrence (％) and density (inds/1 hr tow) were calculated as 61％ and 17inds/1 hr tow at the NECC, 35％ and 6 inds/1 hr tow at the boundary, and 32％ and 15 inds/1 hr tow at the NEC. The distributional pattern of juvenile skipjack tuna was different by year. The characteristics of the horizontal distribution of juvenile skipjack were as follows. During 1992 and 1994, juvenile skipjack tuna were relatively abundant in the southern area but poor in the northern area. During 1995, high concentrations of juveniles in the eastern area appeared. During 1993 and 1996, wider distributions with no clear differences between localities were observed. Young skipjack were collected only from the NECC at night, and were distributed mainly in the lower portion of the mixed layer. The vertical distribution of skipjack changed with growth stages. For daytime in the NECC, larvae at the metamorphosis stage of around 10 mm SL are distributed through depths of 0-200m, and juveniles after metamorphosis of 10-40 mm SL are distributed through depths of 0-220m. Juveniles of 50-60 mm SL are distributed through depths of 60-140 m. Juveniles of 70-80 mm SL are concentrated at about 90m depth. The vertical distribution of juvenile skipjack is related to the vertical temperature profile, with a shallower thermocline corresponding to a shallower distribution of juveniles and a deeper thermocline resulting in a deeper distribution of juveniles. The vertical distribution of juvenile skipjack is also related to the distribution of other organisms sampled. This result indicates that juvenile skipjack are preferentially distributed in the abundant layers of other organisms collected by the midwater trawl net. In contrast, other juvenile tuna, Thunnus spp. including yellowfin tuna Thunnus albacares and bigeye tuna Thunnus obesus are mainly distributed in the mixed layer shallower than about 80 m depth in the NECC, indicating a clear difference with juvenile skipjack. The physical charasteristics of distribution area of juvenile skipjack is mainly from 20 to 29˚C temperature and from 33.6 to 35.5PSU salinity. Those of other juvenile tuna ranged from 26 to 29 ˚C temperature and from 33.6 to 33.7PSU salinity. These results indicate that skipjack and other tuna juveniles have habitat segregation in the pelagic ocean of the tropical western Pacific. The stomach contents of skipjack and other tuna juveniles collected from the NEC and NECC areas were analyzed. The importance of each organism as a prey of skipjack or other tuna juveniles was evaluated by the index of relative importance of prey taxa (IRI). The IRI of fish larvae for juvenile skipjack was remarkably high, 14107 in the NEC and 10852 in the NECC. These data indicate that fish larvae are the principal diet of juvenile skipjack. In the NEC, Euphausiacea (IRI＝162), Amphipoda(9.2), and Copepoda(0.3) appeared. In the NECC, Copepoda (IRI＝158.4), Cephalopoda (66.8), Euphausuiacea (24.8), and others including Saggitoidea, Isopoda, and fish eggs (11.6), and Amphipoda (2.1) appeared. Unidentified organisms comprised the second-highest score of the IRI, 214.4 in the NEC and 346.5 in the NECC. These organisms were consisted mainly of digested fish larvae. Diel periodicity of feeding activities of juvenile skipjack was studied, based on the temporal change in the stomach content index (SCI), stomach fullness, and digestion index. The percentage of empty stomachs was 100％ at 22-02 hours, 80％ at 02-06 hours, and decreased rapidly after sunrise, reaching the minimum score of 5.3％ at 14-18 hours（before sunset）. In contrast, the percentage of full stomachs reached the maximum score of 60.6％ at 14-18 hours, and decreased to 0％ from 22 to 06 hours. The SCI and digestion index also indicated the maximum score at 14-18 hours in contrast with the minimum score at before sunrise. Therefore, juvenile skipjack are actively feeding during daytime from morning to sunset, but they do not feed at night. The stomach contents of other juvenile tuna were characterized by extremely high scores of fish larvae with no clear difference between the NEC and NECC ; the only occurrences of other prey organisms were Euphausiacea and Cephalopoda. These data show that other tuna are stronger piscivourous feeders than skipjack during the juvenile stage. Feeding activities of other juvenile tuna occur during daytime, similar to skipjack juvenile. In order to clarify the growth of skipjack during the early life stages, daily otolith increments were analyzed. Samples from skipjack larvae and juveniles were collected during 1994 to 1997. The otolith measurement system (Ratoc System Engineering Inc., Tokyo) was used for counts of growth increments and measurements of increment width. Daily growth increments were validated by marginal increment analysis for juvenile skipjack. Growth rate from larva to juvenile stages of skipjack was studied using the relationship between body length and the number of daily increments of 548 individuals（3.3 to 57.7 mm SL）. In 15 samples from 1996 and 1997 (3.3 to 7.8 mm SL), daily growth rate was slow, 0.55 mm /day at 3 to 9 days old. In 285 samples from 1994 (9 to 24 days old）, daily growth rate rapidly increased to 3.3 mm /day, and for 248 samples from 1995 (9 to 29 days old) growth was 2.5mm /day. The estimated length at 30 days after hatching was about 60 mm SL. After metamorphosis from larva to juvenile at 10 to 12 days after hatching, a period of extremely rapid growth with large individual variation was observed. Juvenile skipjack growth rates depend on hatching year and nursery area. The analyses of distance from core to margin at each otolith increment show that a larger individual had a faster growth period after 5 days after hatching. A rapid growth in the early life stage enables the utilization of larger prey organisms, resulting in increased survival rates in the nursery ground that are nutritionally poor. Consequently, these characteristics play an important role in maintaining the population level of skipjack in the pelagic ocean of the tropical western Pacific. | |||||
| 言語 | en | |||||
| 書誌情報 |
ja : 水産総合研究センター研究報告 en : Bulletin of Fisheries Research Agency 巻 3, p. 63-132, ページ数 70, 発行日 2002-03 |
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| 出版者 | ||||||
| 出版者 | 水産総合研究センター | |||||
| 言語 | ja | |||||
| ISSN | ||||||
| 収録物識別子タイプ | PISSN | |||||
| 収録物識別子 | 1346-9894 | |||||
| 書誌レコードID | ||||||
| 収録物識別子タイプ | NCID | |||||
| 収録物識別子 | AA11589591 | |||||
| 情報源 | ||||||
| 識別子タイプ | Local | |||||
| 関連識別子 | fra_k_3_63 | |||||
| 関連サイト | ||||||
| 識別子タイプ | URI | |||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010651116 | |||||
| 関連名称 | 日本農学文献記事索引（AgriKnowledge） | |||||
| 著者版フラグ | ||||||
| 出版タイプ | VoR | |||||
| 出版タイプResource | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |||||
