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東北海域における動物プランクトンの動態と長期変動に関する研究
https://fra.repo.nii.ac.jp/records/2007409
https://fra.repo.nii.ac.jp/records/20074091ba1878c-8b6c-40d7-90ca-214dc76c2d11
| Item type | 紀要論文 / Departmental Bulletin Paper(1) | |||||
|---|---|---|---|---|---|---|
| 公開日 | 2024-06-10 | |||||
| タイトル | ||||||
| タイトル | 東北海域における動物プランクトンの動態と長期変動に関する研究 | |||||
| 言語 | ja | |||||
| 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 | metadata only access | |||||
| アクセス権URI | http://purl.org/coar/access_right/c_14cb | |||||
| 著者 |
小達, 和子
× 小達, 和子 |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | The sea area of the western North Pacific Ocean off the northeastern part of Japan is called the Tohoku Sea Area. The hydrography of the sea area is complicated by influences of the Kuroshio Extension, the Oyashio Water, and the Tsugaru Warm Water systems. The sea area is one of the most productive fishery grounds in the world. The present study aims to reveal long-term variations of zooplankton biomass, which are preyed upon by pelagic fishes that migrated to this area, and to evaluate the functional role of the zooplankton community in relation to the fishery resources. 1. A total of 17,242 zooplankton samples collected from the Tohoku Sea Area between 1951 and 1990 was examined in this study. The samples were taken by vertical hauling of a conventional net, so called Marutoku net (net opening 45 cm, mesh aperture 0.33 mm) from 150 m depth to the surface. Using the collections, wet weight measurements and identifications to species were conducted. Long-term variations of zooplankton biomass and distributions of the dominant species were investigated. Relatively small variations of water temperature are observed at a depth of 100 m. The Oyashio Front and the Kuroshio Front are commonly represented by the Counter lines of 5 and 15℃ at that depth, respectively. The present study also divided the Tohoku Sea Area into these three water masses based on this water temperature at a depth of 100 m, that is, the Oyashio Water (<5℃), the Transitional Water (5-15℃), and the Kuroshio Water (>15℃). 2. Monthly mean biomass of zooplankton within grids of every one degree of latitude and longitude was calculated for all the data collected. The biomass of zooplankton between January and March was less than 1 g/net although the sampling area covered only the western part from 150°E off the Joban Coast. High biomass was observed from May to October, during which observations occupied the whole of the Tohoku Sea Area. In particular, biomass of more than 10 g/net was commonly observed off the Sanriku Coast, the eastern Hokkaido, and the southern Kurile Islands. From November to December the biomass became small again to level as observed from January to March. The extensive survey conducted off the Joban and the Sanriku Coasts to the meridian of 160°E in May of 1973 revealed that high biomass occurred in the Kuroshio Water (>15℃). Observation along the meridian of 145˚E conducted in September of 1986 also showed that zooplankton was abundant in the Oyashio Water and less so in the Transitional and the Kuroshio Waters. These results indicated that distributions of zooplankton are largely affected by the oceanographic conditions. 3. The rage of water temperatures at the sampling sites was among 0.1 and 24℃. The highest biomass of zooplankton (34.1 g/m2) occurred in the lowest water temperature rage (0-1℃), Zooplankton biomass decreased with increasing water temperature. Mean abundance in water temperature rages of 5-10, 10-15, and >15℃ were 11.6, 7.4 and 6-5 g/m2, respectively. Ninety-seven percent of samples were less than 20 g/m2 in the Kuroshio Water, while only the 51% was less than 20 g/m2 in the Oyashio Water. 4. Seasonal changes in the zooplankton biomass were also investigated in the Tohoku Sea Area. The annual maximum biomass usually occurred in May in the Oyashio Water. Eighty percent of observations in the forty years had an annual maximum in May or June. The mean biomass in May reached 40 g/m2. From May to August the biomass was high (20-30 g/m2) and decreased in autumn. In the Transitional and the Kuroshio Water the biomass was also high in May and decreased in summer, but a small increase of biomass was observed in November. 5. Mean biomass of zooplankton was 17.3 g/m2 in the Oyashio Water, although a long-term variation was noted for the yearly mean biomass. That is, relatively high biomass was observed from 1956 to 1962 (mean biomass, 16.5 g/m2), from 1965 to 1978 (21.0 g/m2), and from 1987 to 1989 (16.3 g/m2). The mean biomass in the Transitional Water was 7.8 g/m2. Year to year variation was also observed in this water mass, but the trend was not as consistent as that observed for the Oyashio Water. In the Kuroshio Water the mean biomass was 5.8 g/m2 with a small year to year variation. 6. Zooplankton biomasses in the three water masses of the Tohoku Sea Area were estimated based on the mean biomass and the area of the respective water masses. The estimates were conducted using data collected in the western sea area from 146°E from 1964 to 1990. During this period the total biomass for the whole Tohoku Sea Area varied between 1.934x 106 and 5.358x 106 ton. The mean biomasses in the Oyashio, the Transitional, and the Kuroshio districts were 1.731 x 106, 1.857×106 and 0.299×106 ton, respectively. In the Oyashio district, year to year variations of the biomass were corresponded to the long-tern variations of biomass and not to the changes of the area of the water mass. This trend was also noted in the Transitional district. 7. A total of 259 species was identified in the present study. Species composition represented well the properties of the water masses from which they were sampled. For example, seven of the 33 species occurred in the Oyashio Water off the Joban and the Sanriku Coasts, were indicator species of cold water masses (e.g., Calanus cristatus, Calanus plumchrus), while ten of 50 species that occurred in the Kuroshio Water were indicator species of warm water masses. In the Transitional Water both cold and warm water species were observed. Fifty-six species were regarded as dominant species based on the rank order of the individual number. Seven species were determined as the most important species in terms of the body weight (Calanus cristatus, Calanus finmarchicus, Calanus plumchrus, Eucalanus bungii, Metridia pacifica, Calanus helgolandicus and Themisto japonica). All of the seven species were indicator species of cold water. Although Paracalanus parvus was numerically dominant (5,886 inds/net), the total abundance of them was equivalent to only 24 individuals of Calanus cristatus. Calanus cristatus and Calanus plumchrus are widely distributed off the Sanriku Coast, the southeastern coast of Hokkaido, and the southern Kurile Islands, which are the main fishing grounds of the Pacific saury, from early summer to autumn. The increase of total zooplankton biomass observed in the Oyashio Water was due to Calanus cristatus and Calanus plumchrus. 8. Pacific saury (Cololabis saira) hatches out in the Kuroshio Water, and stay off the Joban Coast during their juvenile stages. Stomach content analysis showed that they preyed upon small body size copepods of the warm water species in the Joban Sea Area. Pacific saury starts to migrate northward with growth, and reach the Oyashio Water, where zooplankters are abundant. In this water mass they prey on larger body size zooplankters than those eaten in the Joban Sea Area. The mean amounts of stomach contents of Pacific saury (body length, 19-31 cm) were 3-5 g. The amount in small sized Pacific saury was less (2-5 g) and that of larger ones was more (max. 8 g). Although the weight of stomach contents increased with body size, the ratio to body weight was less in large size Pacific saury (4%) than in small size one (7%). 9. Total amount of zooplankton consumed by Pacific saury was estimated based on the growth from the juvenile stage in the northward migration to the adult stage in the southward migration assuming a transport efficiency of 10%. The fisheries of Pacific saury are usually conducted in the latter stage. From 1979 to 1985 the annual mean consumption of zooplankton by Pacific saury was 1.55x106 ton, which was 7-fold higher than the annual mean yield of Pacific saury during the same period. 10. Long-term variation observed in the yield of Pacific saury corresponded to that observed in zooplankton biomass in the Tohoku Sea Area. The present study revealed that zooplankton, especially the most important seven species in the cold water, played an essential role in maintaining resources of Pacific saury in the Tohoku Sea Area which is the main feeding ground of them. The present study shows variations in zooplankton biomass and species compositions in relation to a planktivorous pelagic fish species. The results provide valuable information to investigate fishery resources, especially to consider trophodynamics of zooplankton and plankton feeder in the Tohoku Sea Area. | |||||
| 言語 | en | |||||
| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | 東北海域は,北太平洋亜寒帯水域の西部に位置し,黒潮続流と親潮および津軽暖流等により複雑な海况を呈し,我が国周辺海域で最も漁業生産が高い海域である.この海域に来遊する小型浮魚類が利用する動物プランクトンの質的·量的動態を解析し,それらが魚類資源との関わりに果たす役割を解明することを本研究の目的とした.1. 東北海域において,1951~1990年の40年間に,丸特ネットを用い,水深150m層から曳網採集した動物プランクトン試料17,242点について湿重量の計測と種の同定を行い,現存量の長期変動と重要種の動態について解析した.東北海域の水深100m層水温分布のパターンは一年を通じて比較的変化が少ないので,親潮前線に相当する5℃以下を親潮水域,黒潮前線を指標する15℃ 以上を黒潮水域,それらの間の5~15℃を混合水域に区分して,解析を行った.2. 1951~1990年の月別緯度経度1度枡目の平均採集量の分布によると,1~3月は調査の行われた 150°E以西の常磐水域で1g/net 以下であったが,4~10月は調査が東北海域の全域で実施されるとともに平均採集量も増加し,5~8月には三陸~北海道東~南千島沖水域で10g/net 以上となった.しかし,10月以降は調査範囲も縮小し,採集量も少なくなった.1973年5月の常磐·三陸沖の160°Eに及ぶ広域調査で,動物プランクトンは38°N線以北において水深100m層5℃以下の冷水域に多く,15℃ 以上の暖水域で少なかった.また,1986年9月の145°E線南北縦断採集では,親潮前線以北で多く,混合水域·黒潮水域では少なかった等,採集量は環境条件を反映していることが明らかになった.3. 採集点における水深100m層の水温範囲は0.1~24.0℃ であり,1℃階級ごとの現存量(g/m2)は,0℃台の最低水温階級を最高値(34.1g/m2)として,水温が上がるにつれて減少し,5~10℃で11.6g/m2,10~15℃で7.4g/m2,15℃以上では6~5g/m2と低水準が続いた.親潮·混合·黒潮水域別の採集点ごとの現存量頻度分布は,黒潮水域では20g/m2 までの累計が97%を占めていたが,親潮水域のそれは20g/m2以上の採集点が51%を占めた.4. 東北海域における動物プランクトン現存量の季節変化で,初夏5月にピークが認められた. 親潮水域では40年間に5·6月に現存量のピークが出現する年は80%に達し,初夏の増殖が顕著であった.総平均では5月のピーク(40g/m2)から8月頃まで20~30g/m2の高水準が続き,秋には減少した.混合水域·黒潮水域では5月のピークから夏に減少し,11月頃に小さなピークが見られるという特徴を示した.5. 親潮水域における総平均現存量は17.3g/m2であったが,40年間にわたる長期変動のなかで,3つの高水準期すなわち,第Ⅰ期(1956~1962年,平均16.5g/m2),第Ⅱ期(1965~1978年,平均21.0g/m2),第Ⅲ期(1987~1989年,16.3g/m2)が検出された.平年偏差からもこの傾向は明瞭であった,混合水域での総平均値は7.8g/m2で,漸増から漸減状態は認められたが,親潮水域の変動と同期するような傾向は識別されなかった.黒潮水域の平均値は5.8g/m2で,その変動は小さかった.6. 146°E以西に特定した近海特定区域において,1964~1990年6月の水深100m層の水温分布から,親潮·混合·黒潮区域の占有面積(km2)と現存量(g/m2)の積で動物プランクトン生物量を求めた.この27年間で年別生物量は1.934×106~5.358×106トンの間で変動し,親潮区域で平均1.731×106トン,混合区域で1.857×106トン,黒潮区域では0.299×106トンであった.親潮区域における経年変動は,現存量の長期変動の第Ⅱ期と第Ⅲ期にほぼ並行しており,混合区域においても同様な傾向が明らかになった.生物量は各区域の占有面積よりは,現存量すなわち分布密度とよい相関を示した.7. 同定された動物プランクトンは259種に及んだ.1986年5月の常磐·三陸水域では,親潮水域に出現した33 種の う ち Calanus cristatus, Calanus plumchrus 等の7種の冷水性種が,黒潮水域では50種のうち10種の暖水性種が出現した.混合水域では両水域に分布する種が複合して出現した.平均出現個体数の順位から56種を主要種とし,出現個体数順位で第1位(5,886個体/net)は Paracalanus parvus であった.さらに個体数順位と1個体の体重比から換算して,Calanus cristatus, Calanus finmarchicus, Calanusplumchrus, Eucalanus bungii, Metridia pacifica,Calanus helgolandicus, Themisto japonica の計7種を最重要種と評価した.これら7種は全て親潮系冷水性種であるが,特に Calanus cristatus と Calanusplumchrus は,初夏から秋へかけて三陸~北海道東~南千島沖水域に多く分布して,現存量の高水準を維持するのに寄与し,サンマを始め回遊性浮魚類の漁場域に広く分布することが明らかになった.8. 黒潮流域で生まれたサンマは,稚幼魚期を過ごす常磐水域では暖水性小型橈脚類を主な餌料としているが,6~8月の北上期における未成魚~成魚は前線を越えて動物プランクトンの豊富な親潮水域に回遊し,餌料種も冷水性大型種となる.この時期のサンマ(体長19~31cm)の1個体当たりの平均消化管内容物重量は3~5gであるが,消化管内容物重量範囲は小型魚で2~5g,大型魚では最高8gに達した.体重比でみると小型魚ほど多く摂餌し(7%),大型になるにつれて消化管内容物重量は増えるが,体重比は逆に減少して4% 程度であった.9. 北上回遊期のサンマ未成魚の成長傾向と,南下期に漁獲物の主構成群となる中型·大型群までの増重量から,餌料転換効率を10%として算定した索餌水域におけるサンマの動物プランクトン消費量は,1979~1985年では平均155万トンで,この期間の年平均漁獲量の約7倍を消費したと推定された.10. 東北海域におけるサソマの漁獲量の長期変動は,動物プランクトン現存量および生物量の長期変動とほぼ同期しており,東北海域における動物プランクトンとくに7種の冷水性大型種が,索餌水域においてサンマ資源を支える最重要種であることが明らかになった.以上,東北海域における動物プランクトンの動態および長期変動と,それを利用するサンマとの関わりを解明し,東北海域の生物生産のメカニズムを明らかにするための示唆が得られた. | |||||
| 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 56, p. 115-173, ページ数 59, 発行日 1994-03-31 |
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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 | |||||
| ISSN | ||||||
| 収録物識別子タイプ | PISSN | |||||
| 収録物識別子 | 0049-402X | |||||
| 書誌レコードID | ||||||
| 収録物識別子タイプ | NCID | |||||
| 収録物識別子 | AN00167637 | |||||
| 情報源 | ||||||
| 識別子タイプ | Local | |||||
| 関連識別子 | tnf_k_56_115 | |||||
| 関連サイト | ||||||
| 識別子タイプ | URI | |||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010510438 | |||||
| 言語 | ja | |||||
| 関連名称 | 日本農学文献記事索引(agriknowledge) | |||||
