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音響資源調査によるスケトウダラ(Theragra chalcogramma)太平洋系群の若齢魚の年級豊度推定
https://fra.repo.nii.ac.jp/records/2010812
https://fra.repo.nii.ac.jp/records/201081297ace3da-3fa9-4a58-a8d1-c89ab9ab0ced
| 名前 / ファイル | ライセンス | アクション |
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fra_k_12_25.pdf (10.3 MB)
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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 | 音響資源調査によるスケトウダラ(Theragra chalcogramma)太平洋系群の若齢魚の年級豊度推定 | |||||||||||
| 言語 | ja | |||||||||||
| タイトル | ||||||||||||
| タイトル | Abundance estimation of the young cohorts of the Japanese Pacific population of walleye pollock (Theragra chalcogramma) by acoustic surveys | |||||||||||
| 言語 | en | |||||||||||
| 言語 | ||||||||||||
| 言語 | jpn | |||||||||||
| キーワード | ||||||||||||
| 言語 | en | |||||||||||
| 主題Scheme | Other | |||||||||||
| 主題 | walleye pollock; Theragra chalcogramma; Japanese Pacific population; acoustic survey; abundance estimation | |||||||||||
| 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 |
本田, 聡
× 本田, 聡
WEKO
617
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| 抄録 | ||||||||||||
| 内容記述タイプ | Abstract | |||||||||||
| 内容記述 | The Japanese Pacific population of walleye pollock (Theragra chalcogramma), which is distributed widely along the Pacific coast of Hokkaido and Tohoku, is one of the most important fishery resources in Japan. One of the features of this population in recent years is the occasional occurrence of dominant year classes. Once a strong year class occurs, this cohort accounts for the greater part of the age composition in this population and subsequently sustains good catches for several years. Recognizing the sign of the occurrence of a strong year class as soon as possible before its recruitment is an effective measure to assess the consequent quantitative situation of this population in the years ahead. Quantitative echo sounder has been well developed as one of the oceanographic observation equipments during last few decades; it is widely used for direct stock estimations of marine organisms at present. In this study, hydroacoustic surveys were applied for the quantitative evaluation of young cohorts of the Japanese Pacific population of walleye pollock, which had not evaluated by the orthodox method of stock analysis because of their pre-recruitment size. Optimum conditions and the seasons to accomplish the acoustic survey are presented from the viewpoint of the features of the survey equipment and other conditions to conduct the surveys. The attenuation of acoustic energy due to the effects of sailing was measured on the R/V Kaiyo-maru No. 3, which was used for the acoustic survey cruises. The attenuation by sailing appeared with the increase of the ship speed. In particular, the attenuation was apparent under the head sea condition of sailing; maximum attenuation was attained 1.3dB at 38kHz, 0.7dB at 120kHz. Furthermore, the attenuation by sailing occurred at slower sailing speeds than that at which the apparent attenuation was recognized on the echogram. This means that the attenuation by sailing exerted an influence upon the acoustic data without the operator being aware of it. On the planning of the acoustic survey by the R/V Kaiyo-maru No. 3, setting the sailing direction in a following sea will prevent the underestimation of the acoustic biomass index caused by the attenuation by sailing. Considering the weather conditions, various kinds of fisheries activities that would obstruct the grid surveys or trawl towing, and the overall schedule of the stock assessment of this population, early summer (June till July) was proposed as the optimal season for the acoustic survey aimed at juvenile pollock in the Pacific coast of Hokkaido. Distribution, ecology and the estimation of the standing stock at age of walleye pollock was described by the combined acoustic and trawl surveys conducted on the continental shelf and slope area in the Pacific side of Hokkaido from Jun. 1996 to Jan. 2002. The shoals of the young cohort of walleye pollock often occurred on the continental shelf area of the offshore southeastern Hokkaido. Apparent diel vertical migration of pollock appeared in every season and whole age groups. The range of the vertical migration varied with age/- size and season. Since the echo sounder has acoustical invisible zones both in the surface and the off bottom area, diel or seasonal variation of the swimming layer would cause the fluctuation of the stock estimation. Seasonal variation of the abundance estimation was wider than the diurnal variation; estimated standing stock in early summer was always larger than the results based on the data taken in winter. Emigration of the fish shoals from the survey area, underestimation caused by the bottom acoustic deadzone, increasing of the acoustic attenuation by sailing under rough weather, were assumed as the potential causes for the decrease of estimated abundance in winter. For young cohorts of pollock in early summer, acoustically estimated abundances based on the daytime survey were always larger than those based on nighttime survey. Surfacing of fish shoals toward the undetectable surface layer by echosounder in nighttime was considered as the main cause of the more conservative abundance estimation. Correspondence of the structure of walleye pollock shoals to the habitat conditions was investigated. In the present procedure of the allocation of acoustic energy from the pollock shoals to each age group, both age composition and the average sizes at age of each pollock shoal, taken from the trawl operations, are indispensable parameters. If we estimate both parameters of pollock shoal structure using the information of their habitat location instead of the numbers of trawl tows, we could reduce the effort for conducting trawl operation. The same as other demersal fishes, an age-dependent bathymetric pattern was observed; age composition biased younger in shallower coastal area, then gradually become older with the depth increasing. Furthermore, average sizes at same cohort also tended to be larger in proportion to the increasing depth. Using these relationships as regression functions, the age/size structures of walleye pollock shoals were estimated from their distribution depth and the area was then compared to the real structures of pollock shoals taken by trawl tows. Although the average size at age in the pollock shoal was well reproduced and matched with the real data, the age-composition ratio could not be reproduced from the regression function of the depth. Particularly, since the age-1 cohort appeared patchily on the shallower half of the continental shelf, a simple regression function explained by the depth and area could not well describe their elusive distribution pattern. This negative result consequently confirmed the need of direct biological sampling with the acoustic survey simultaneously for interpretation of the acoustically detected fish shoals. Geostatistics was applied to evaluate the precision of the abundance estimation and the optimal transect interval for the acoustic surveys. By applying geostatistics, standard error of mean (SEM) of the estimator was extensively reduced. This was caused by the existence of the autocorrelation among the data taken from the neighboring transects. If applying the orthodox statistics into the systematic parallel transects survey design, it neglects the autocorrelation among the neighboring data and regards them as mutually independent. Therefore, applying orthodox statistics into the systematic parallel transects survey design overestimated the variance of the abundance consequently. Although the point estimator itself was not varied regardless of the statistical method, applying geostatistics could show the correct level of variance of the estimator. Results of the simulation of varying the transect interval showed that narrowing the intertransect distance would improve the precision of the abundance estimation of young cohorts of pollock. However, narrowing the transect interval increased the total survey distance and therefore the necessary time to run. Considering the expansion of the survey area and the allowable shiptime, the present transect distance of 8 nautical miles was regarded as practical to accomplish the whole survey with an acceptable level of precision. In the case of young cohorts of pollock such as age－1 to－3, significant positive regression line was fitted on the correspondence between the acoustically estimated standing stock at age off southeastern Hokkaido (the Doto area) and the total abundance at correspondent cohort derived by VPA analysis a few years later. These results meant that the acoustically estimated standing stock of young cohorts of walleye pollock in the Doto area well reflected the total magnitude of these cohorts in the whole distribution, despite the Doto area is just a part of the whole distributional area of this population. By applying these regression functions, the total abundance of the young cohorts those have not been recruited or have just recruited recently can be forecast immediately. That is, the acoustic survey for young cohorts of pollock well complement the weak point of VPA on the process of the fish stock evaluation. | |||||||||||
| 言語 | en | |||||||||||
| 抄録 | ||||||||||||
| 内容記述タイプ | Abstract | |||||||||||
| 内容記述 | 近年,北海道太平洋海域に分布するスケトウダラ(Theragra chalcogramma)太平洋系群では,数年間隔で卓越年級群の発生が観察されている。卓越年級群の発生は,その後数年にわたって資源状態に多大な影響を与えることから,新規加入群の豊度を出来る限り早く把握することは,短期的な資源動向予測を行う上で非常に有効である。一方,水産研究所ではスケトウダラの資源解析に Virtual Population Analysis(VPA)を用いているが,その手法の特性上,漁獲開始から数年を経過した年級群については過去に遡って精度良く評価できるのに対して,漁獲情報の蓄積が乏しい最近年の若齢魚の年級豊度を正確に推定することは困難である。本研究では,このVPAの弱点である最近年の若齢魚の量的評価を補完する試みとして,音響資源調査によるスケトウダラ幼魚·若齢魚の年級豊度の直接推定を実施し,その有効性について検討した。調査船による音響資源調査の結果,スケトウダラ若齢魚は初夏および冬季のいずれにおいても襟裳岬周辺から釧路沖にかけての北海道東部太平洋海域(道東海域)の陸棚域を中心に分布した。調査時期の違いによる現存量推定値の変動は,昼夜による変動よりも大きく,同じ年級群の現存量が毎冬の調査で減少し,翌年初夏の調査で再び増加する傾向が示された。この原因として,魚群の日周鉛直移動の影響や魚群の逸散などの可能性が示唆されたが,各要因の影響の有無あるいは程度を特定するには至らなかった。音響資源調査で推定した,年別,季節別,年齢別現存量のうち,初夏の道東海域に分布するスケトウダラ1歳魚の現存量推定値と,その翌年度以降にVPAによって過去に週って推定されるスケトウダラ太平洋系群全体での若齢魚の年級豊度との間に,有意な正の直線回帰関係が得られた。これは,音響資源調査によって得られた加入前のスケトウダラ1歳魚の現存量推定値が,その翌年度以降に徐々に判明する新規加入群量と比例関係にあることを意味する。音響資源調査の実施年数が少ないため,現状ではVPAの結果と比較できるデータが限られているものの,新規加入群が卓越年級群かあるいは低い年級豊度であるかの判断には十分に有効であることが示された。今後調査が継続する中で,デー夕数が増えることにより,回帰関係の信頼性が向上し,より高い精度での年級豊度の予測が可能となると期待される。 | |||||||||||
| 言語 | ja | |||||||||||
| 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 12, p. 25-126, ページ数 102, 発行日 2004-11 |
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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_12_25 | |||||||||||
| 関連サイト | ||||||||||||
| 識別子タイプ | URI | |||||||||||
| 関連識別子 | https://agriknowledge.affrc.go.jp/RN/2010710398 | |||||||||||
| 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 | |||||||||||
