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北西太平洋系サンマの回遊機構の綜観的解析
https://fra.repo.nii.ac.jp/records/2007259
https://fra.repo.nii.ac.jp/records/2007259eecf5aa0-4057-4a38-a1ca-e6e1676409b2
| 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 | 北西太平洋系サンマの回遊機構の綜観的解析 | |||||
| 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 |
福島, 信一
× 福島, 信一 |
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| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | Pacific saury, Cololabis saria (BREVOORT), is one of the most important commerical fishes exploited in the Northwest Pacific Ocean, especially in the waters around the central Kurile, southeastern Hokkaido and northeastern Honshu. The fishing activities are now concentrated in rather short period of a year from September to November. The fisheries have experienced tremendous fluctuations in fishing conditions such as amount and size composition of the catch, location and time of the successful operations, etc. Many studies were, therefore, conducted in order to understand the fluctuations. But lack of long series of detailed data kept the previous works at such a level as to broadly describe average features of fishing and oceanographic conditions, not permitting to provide means of pre-season forecasts of the stocks. The present study aims at establishing methods to predict abundance, size composition and distribution of saury stocks available to the fishery around Japan in advance to each fishing season. Investigated in the study are (1) long-term information on fisheries both in methods of fishing localities of operations and amount of catch, (2) biological data of fish, especially distribution, size and maturity, and (3) hydrographic and other environmental data, obtained from 1950 to 1970 by nation-wide cooperative surveys and literature investigations. Additional data are also analyzed for reviewing the distribution and abundance of the species in the 1970's. Pacific saury has long been fished in various parts of Japan in particular seasons of the year. Traditionally the fishing activities have been most developed in the Pacific waters in this country. The first significant fishing method to capture the species was purse seining. This method was recorded as early as around 1670 in southern Japan. The fishing grounds were limited only coastal zones of 10 nautical miles around peninsulas. In 1905, drift netting was found more efficient than the traditional pursing, and the former soon replaced the latter. The new method does not need large numbers of crew and boats, and so maneuverable as to exploit fish distributed in offshore waters beyond the traditional grounds. Eventually the drift net fleet soon exploited deep grounds off the Tohoku Region around Lat. 35°N to 40°N. For many years the saury fishery was one of the "free fisheries", or "fisheries that can be arbitraily operated by any willing body", in the Japanese fisheries law. In 1933, the saury drift net fishery was included into the "Minister's approved fisheries" or "fisheries that can be operated only by bodies who are approved by the responsible minister (.e.g Minister of the Agriculture, Forestry and Fisheries since 5 July 1979) as such". In other words, the saury drift net fishery has then been regarded so effective as to need any monitoring on its fleet size. In 1949, the saury fishermen introducted more efficient stick- held dip net with attracting lumps, known as bouke ami in Japanese language. Since then the fishing grounds expanded rapidly toward offshore waters and the amount of catch increased drastically, and the saury fihsery is enumerated one of the most important fishing operations during the autumn in Japan. Figure 6 shows the fishing grounds and the annual production of saury for each of the three era of different fishing methods. Wide areal coverage of the commercial operations since introduction of stick-held dip net benefited not only fishermen but also biologists. The catch records from fishing vessels have provided information required to develop ecology of saury, together with related oceangoraphic and biological surveys undertaken on board research vessels. The following paragraphs cover major finding on seasonal distribution and migration of the species. Pacific saury immigrate the Tohoku Region in April or May following rapid northward expansion of the Kuroshio Current. Shoals move northward along branches of the Kuroshio. In May the fish are most frequently found in the mixture waters of the Kuroshio and Oyashio Currents. The distribution range then steady approaches the Oyashio Front in June. During the northward migration in the early summer the larger fish are always found in the northern part of distribution range while the smaller in the southern waters. When the Kuroshio branches significantly expand northward after the rainy season is over in early or middle July, the fish cross the Oyashio Front and reach a conspicuous front off the Kurile Islands, which is called the Convergence off Eastern Kurile or simply the Kurile Front hereafter in this report. Saury aggerate at the warmer side of the Kurile Front where zooplanktons are so densely concentrated as to form prolific feeding grounds of the fish during summer months (Figure 12). Dominant forage species include Calanus cristatus KROYER, C. plumchrus MARUKAWA and Themisto spp. In early and middle August the fish start the southward migration from the Kurile Front and surrounding waters. There appear sevral groups of migrants. Large-sized fish of 30 cm in modal length immigrate the northern part of distribution range, reaching as north as Lat. 47°N to Lat. 50°N. In such northern waters, the fish are liable to be exposed to cold water below 6˚C (Figures 12 and 21). It should be also noted that the length of day time changes significantly then and there. For instance, from 10 July to 10 August, the day time reduces by 64 minutes at Lat. 45°N, while by 42 minutes at Lat. 35°N (Figure 28). Presence of cold waters near the distribution range and significant reduction of day time must stimulate sexual maturation of large-sized fish that will spawn within a few months, and drive them to the spawning grounds near the Kuroshio Front. Medium- and small-sized fish are sexually immature in the summer and continue northward migration seeking food plankton even in early August (Figure 22). After the temperature starts to lower in middle August the fish turn to southward migration. Thus four or five groups are recognized in fishing grounds off southeastern Hokkaido, where the first group usually appears late August. Major fishing grounds form first in early and middle September in areas between southeastern Hokkaido and northern Sanriku (Figure 46). The Sanriku area extends between Lat. 38°N to Lat. 41°30'N, along the northeastern coast of Honshu. In the northern waters the fishing activities occur over southward projection of the Oyashio Intermediate Water of 2˚C at 100 m depth layer (Figures 46, 49 and 50). Figure 46 also shows that a warm water mass or masses frequently occur around southeastern Hokkaido in September. Positions of the intermeditate cold water and then the early fishing ground are affected by pressence and by position of the warm water mass. The pronounced water mass drives the exploitable shoals toward offshore (e.g. 1960 and later years). When the warm water mass is absent or small, the fish are caught mostly in the nearshore waters. The Intermediate Cold Water of 2°C once disappears in the waters south of the northern fishing grounds until it is found again but at deeper layers around 300 m off Joban, Lat. 35°N-38°N, or at times off southern Sanriku (Figures 51-54). In the middle area without the intermediate water the fish move quickly and most of them are found forming sinking shoals or Sokomure. Most fish leave the northern Tohoku Region (Sanriku and north) in late November, and stick-held dip net fishery clases the fishing season. In the following winter months, the majority of fish enter into the waters around the Kuroshio Current and the Counter Current, north of the Subtropical Convergence (Figures 42-44). Attention of biologists and fishermen is directed toward distribution and abundance of fish in September that determine success of fishing in that season. The remarkable change of intensity of the Kuroshio Current and the resultant east-west shift of the Oyashio Current insert definite influence on the formation of the early fishing grounds in September either in nearshore or in offshore waters (Figure 56). Figure 57 shows yearly average position of the northern tip of the Kuroshio Current in the Tohoku Region. It is evident that the average northern most path shifted from about Lat. 38°N in the early 1950's to Lat. 36°N or even south in the late 1960's, and then moved northward. Beside this long-term shift, there appears another short-term cycle with a period of four and half years. The northward expansion of the Kuroshio drives the southward flow of the Oyashio Current westwardly or toward the northern Tohoku Region. When the Kuroshio stays in the south, the warm water mass develops off southeastern Hokkaido and affects the Oyashio so as to make the major southward flow passing east of the warm water mass or toward the offshore. Such shift of the currents resulted in change of not only location of early fishing grounds but also size composition and abundance of the stocks. Taking the northernmost position of the Kuroshio Current into consideration, there are recognized four periods in the twenty years from 1950 to 1969, and the fifth in the 1970's. First the northern tip of the Kuroshio Current continuously reached Lat. 38°N every year during 1950 through 1953. The northward expantion of the Kuroshio was associated with development of the first branch (western-most flow) of the Oyashio Current. The fishing grounds formed in the nearshore waters, expanding as south as the Joban. The fishing operations occurred widely extending southward to Joban, and lasted for three months until middle December. Reflecting the large stock of immigrants, the amount of catch reached around 200 000 tons even though then the saury fishery was at the very early stage of development of the stick-held dip net introduced in 1949 just after the complete destruction of the fleet during the War. Medium-sized fish of 27-28 cm in modal length dominated in the catch. The Kuroshio did not reach north of Lat. 37°N in the summer of 1954. In the season the large-sized fish of 30 cm in modal length replaced the medium-sized fish. The amount of catch was 292 000 tons. This drastic change of fishing conditions was followed by the second phase of fishing until 1958. The Kuroshio reduced its intensity in the Tohoku Region, and the northern tip stayed around Lat. 37'30'N. The Oyashio Current projected two pronounced branches, the first branch close to Honshu and second at east of Long. 145°E. The water temperature in Sanriku was high in 1955, 1957 and 1958 but low in 1956. The saury stocks were abundant in all the four years. Fishing season lasted until late November, with successful operations in wide range as south as off Kinkasan, Lat. 38°N-39°N and Joban of Lat. 35°N-38°N. Amount of catch exceeded 400 000 tons in the three warm years when both large - and medium-sized fish, 30 cm and 27-28 cm in modal length, respectively, were exploited and the medium-sized fish stayed long in the major fishing ground off Sanriku. In the cold season of 1956, the medium-sized fish dominated over the large-sized fish. The first branch of Oyashio extended toward Lat. 38°N, and then saury did not stay off Sanriku. The amount of catch in 1956 was 360 000 tons, less than in the three warm years. The Kuroshio again shifted southward with the northern limit at Lat. 36°10'N in 1959. Dominant medium-sized fish in this season were smaller in size, 26-27 cm, than in previous years. The abundance was on the decrease but the catch still amounted 400 000 tons possibly due to intensified fishing activities. The following four years between 1960 and 1963 form the third stable phase characterized by further southward shift of the Kuroshio, south of Lat. 37°N. The first branch of the Oyashio Current along the coast was weak while the second branch developed in the offshore around Long. 147°E-148°E. Most fishing activities occurred in the offshore grounds near the second branch. Operations in the southern ground of Joban were not successful in three years except 1968 when abnormally cold water hit Pacific coast of Japan. The yearly catch stayed around 300 000 tons, mainly comprising both large- and medium-sized fish of 30 cm and 26-27 cm in modal length. In 1964, the northern tip of Kuroshio shifted further south to Lat. 35°55', and medium-sized fish decreased in abundance. This season initiated the fourth phase up to 1968 with alternative oscillation of the northern path of Kuroshio that stayed around Lat. 36°N. The southward shift of Kuroshio accompanied eastward expansion of the warm water mass off southeastern Hokkaido, and then further contraction of the second and third branches of the Oyashio Current. The distribution range of saury stocks shifted eastwards year-after-year, and the major fishing grounds formed around the Oyashio Front in offshore waters or even in the high sea as east as Long. 150°E. Catch off Joban was very poor. The shoals were scattered in the whole fishing grounds, and dominated by smallsized fish of 24-25 cm in modal length. Amount of the landings stayed very low, hardly reaching about 200 000 tons. The poorest catch of 52 000 tons was recorded when the Kuroshio stayed at the southernmost position of Lat. 36°N in 1969. The fishing activities were fragmental, mostly limited to the offshore waters of Long. 144°E to 160°E. The catch mainly consisted of small-sized fish of 24-25 cm in modal length. The fifth phase from 1970 to 1973 then follows. During the four years, the northern path of Kuroshio gradually returned to Lat. 36°30'N on the average, having fluctuated between 36°10'N in 1970 and 37°N in 1973. The Oyashio Current approached Honshu, and then fishing grounds also shifted coastwardly. Some fishing occurred off Joban since 1972. Major size group in the catch was small in 1970 and 1971, but medium in 1972 or large in 1973. Amount of catch also recovered to 200 000 tons. The Kuroshio moved once to south, hardly reaching Lat. 36°N in 1974. But northward shift of the current continued in 1975 to 1979. Accordingly the warm gyre off southeastern Hokkaido contracted and the Oyashio approached Honshu. Immigrants to the coastal waters increased and fishing activities were intensified in the southern Tohoku including Joban. Medium-sized fish occurred constantly every season, and amount of the catch recovered to a level of around 250 000 tons. Such chronological changes are illustated in Figures 46 and 56 for positions of the Kuroshio and fishing grounds, and Figure 47 for amount and size composition of saury catch. The following table depicts the aforementioned oceanographic and fishing changes related to the northern most position of the Kuroshio Current. The review summarized in this table indicates that amount of catch was large in years when the fish immigrate nearshore waters and reduced with eastward shift of major fishing grounds. It is also noted that large catch occurred when both large- and medium-sized fish immigrated fishing grounds. Catch was moderate for years when either one of these two groups was available to the fishery. Only poor catch was obtained when small-sized fish dominated. The present study has elucidated the method of pre-season forecast of distribution and size composition as well as general level of abundance of available saury stocks based on the synoptic information on biology of the species including effects of oceanographic conditions on the behaviour. Further investigations are required to develop methods for estimating the stock size of saury, which will not be easily approached by the conventional population dynamics because the life span is short and because major biological characteristics such as distribution and migration are so changeable due to environmental conditions as to pointed out above. For forecasting the stock size, it is highly desirable to develop methods to evaluate abundance of the fish before exploitable phase, based on larva census, experimental fishing or acoustic surveys. |
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| 言語 | en | |||||
| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | 東北海区のサンマ漁況変動の研究は古くから行われているが,何れも4~5年程度の短期間の平均的な漁獲と海況との関係を概観したもので極めて不充分であった, 1) 本研究はサンマ漁況予測の基礎を確立する目的で,1950年から1970年の間を中心に実施し,1971年以降の情報も収集した,長期間の漁業の変遷を究明すると共に,関係機関の協力を得て収集した漁獲物·漁場形成·海洋構造に関する資料,ならびに補完的·実験計画的に行った海上調査結果の解析により,サンマの回遊特性のいくつかを明らかにした、それらの知見の総観に基づいて,漁場·漁獲物組成および漁獲水準を内容とする漁況予測が試みられるようになった.2) サンマは日本周辺の各地で季節的に漁獲される,太平洋側の漁業は1670年ごろ本邦南岸で旋網を用いて行われていたが1905年に流網が考案され,以来東北海区が主漁場となった.1949年には火光利用棒受網漁法に転換,漁獲も急増し秋の重要漁業の一つとなった、この漁業は自由操業であったが,1933年から取締り規則が制定され所管大臣の承認漁業となった.漁獲量の長年の動きをみると,沿岸来遊群の多寡により増減し,4~5年の短期変動が合した長期変動を示している.最低水準年は 1898·1932·1969年にみられ,凡そ36年の周期性が認められる.3) サンマ群は4~5月ごろ黒潮の急激な増勢に伴って黒潮前線以北へ来遊し,黒潮北上分派沿いに北方移動して6月には親潮前線周辺に停る.魚群は黒潮分派先端部に多く,魚体の大きいものがより北方に分布する.梅雨あけに暖流系水が急に北進する際に親潮前線を越え,千島沖の顕著な潮境(千島東方集連線と命名,千島前線と略称)に達し,前線の暖水側に分布する、この水域にはサンマの餌となる動物プランクトンが極めて濃密に分布し,重要な索餌水域となっている.北限水域に達したサンマは間もなく南下に移る、成長を終えた大型魚は8月上~中旬には親潮根幹水の低温と日長短縮の刺戟を受け,成熟を指向して南下を開始する,一方,成長期の中·小型魚はなお北上·索餌を続け,水温の降下により南下を誘発される,例年8月下旬ごろ南下第1群が道東沖へ来遊する,平均的に魚体の大きい群が先行し,1漁場間には4~5群団が波状的に来遊して南方移動する、漁期末には東北海区北部の残留群が少くなり,冬季には大部分が黒潮周辺および反流域に分布し,亜熱帯集連線をその南限としている.4) 南下初期の主漁場は9月上·中旬ごろ100m層水温2℃の親潮中冷水縁辺上に形成され,親潮が接岸南下すると沿岸に,道東沖暖水塊に接岸を阻まれると沖合へ移る、後期(11月以降)の主漁場は常磐沖の黒潮前線北側の潮境に形成され,親潮系水のこの水域への張り出しの強弱により漁況の年変動が大きい。漁場の海洋構造は前線帯の集連部から冷水側へ僅かに離れ,鉛直安定度が大きく,下層には親潮中冷水が張り出し,顕著な潮境が上下に走っている、中冷水は三陸沖で100m,常磐沖で300m前後に分布するが,ソコ群れ(潜没群)が多く、南下速度が早い10月中·下旬には認められなかった.5) 親潮主勢力と初期サンマ主漁場位置の年代的な離岸·接岸の根源は黒潮流路北限の南北振動である。主漁場は黒潮が北にあると親潮の接岸南下が顕著で沿岸に,南偏すると道東沖暖水塊が発達して親潮の接岸が阻まれ,沖合に形成される、黒潮流路はほぼ4年半の周期性をもって減衰振動しながら段階的に南へ移り,再び北へ移り始める.それに伴う水塊配置の型·主漁場位置·魚体組成および漁獲水準は次のように類別される. 漁獲水準は沿岸来遊群が多い年代は高く,資源の相対的分布重心の東偏に伴って低下する、また大·中型魚の双峯年代には高く,何れか片方だけでは中漁程度で,小型主体年代には低い,6) 漁況予測は重要課題であるが,サンマは短命で,魚群分布·移動の生物学的特性が,海洋学的特性に影響され易いので,数理学的な予測は現段階では難かしい,そこで漁業の変遷と動向および回遊に関する生物学的·海洋学的特性の相互関連など,総観的知見に基づいて予測している,漁場形成·漁獲物組成は比較的高い精度で予測できるが,漁獲水準については今後さらに研究を深める必要がある、魚群分布量の把握のためには,探索技術の習熟,新鋭実測機器の導入と方法の開発,あるいは稚仔魚の時空的分布量から予測する方法の確立が重要である. | |||||
| 言語 | ja | |||||
| 書誌情報 |
ja : 東北区水産研究所研究報告 en : Bulletin of Tohoku Regional Fisheries Research Laboratory 巻 41, p. 1-70, ページ数 70, 発行日 1979-12 |
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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 Regional Fisheries Research Laboratory | |||||
| 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_41_1 | |||||
| 関連サイト | ||||||
| 識別子タイプ | URI | |||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010212443 | |||||
| 言語 | ja | |||||
| 関連名称 | 日本農学文献記事索引(agriknowledge) | |||||
