北西太平洋におけるサンマの生活史とそれにもとづく資源変動の考察

小坂, 淳

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北西太平洋におけるサンマの生活史とそれにもとづく資源変動の考察

https://fra.repo.nii.ac.jp/records/2007445

Item type

紀要論文 / Departmental Bulletin Paper(1)

公開日

2024-06-10

タイトル

北西太平洋におけるサンマの生活史とそれにもとづく資源変動の考察

言語

jpn

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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

metadata only access

アクセス権URI

http://purl.org/coar/access_right/c_14cb

著者

小坂, 淳

抄録

内容記述タイプ

Abstract

内容記述

I Purpose and method In the research of fish resources, the elucidation of the life history of the object species is basically one of the important problems. Hotta (1960) published as the following opinion about the life history of the Pacific saury. "One population is composed of the largest and the middle groups, which presumably hatched in early spring to early summer (March to June), called the spring spawning saury. The middle sized group and largest size group are one and a half year old in the former, two and a half year old in the latter, and hatched in the spring of the previous year. The other population is composed of the larger and smaller groups, which presumably hatched in late autumn to winter (October to February), called the autumn spawning saury. Concerning the growth of each size group in autumn spawning saury groups, the larger sized group is two years old and the smaller sized group is one year old." Afterwards, the change phenomenon of the resource which was not able to be explained had occurred when basing on his opinion. The life history is newly reviewed, and there is no research by which the resource fluctuations are considered though there is a negative opinion from the standpoint of population genetics to his theory. This research aims to elucidate the life history of Pacific saury completely. The upheaval line interval of the scales and the change in the transparency of the otoliths were objectively examined, and the method of adequately determining the growth process was established concerning the problem of the age and growth. Moreover, to understand the development process of the ovarian eggs, observations and measurements were done by histological methods about the reproduction. In addition, to elucidate distribution, movement and migration, etc. investigations by ship was executed in a wide-ranging sea. The amount of the resource was assessed based on a new method, and consideration of the resource fluctuation was added. The material used is data of body measurements and fishing reports of Pacific saury collected by the Tohoku national fisheries research institute and related organizations in the whole country over 36 years from 1951 to 1988.
II Results
1. Life history
1) Growth The upheaval line interval of scale of large fish is about 1.3mm wide, and about 2.3mm narrower from the center. The interval broadens a little when further parting from the center, and the interval is narrow again in the part of the scale in the surrounding. Then its interval in scale of middle fish broadens most in about 1.5 mm, and narrows gradually afterwards. The interval for the small size group broadens from the center by about 1.3mm, and narrows afterwards. It is thought that the annual ring is formed with this in about 2.3mm in the radius in scale of the large size group. When scalation was observed again, the annual ring is not formed in almost the middle size group and the small size group though one annual ring was observed in the majority of scales of the large size group. When the change in the upheaval line interval in a group to which the annual ring is formed and a group not so is seen, the former is corresponding it of the large size group and the latteris almost corresponding to it of the middle size group. It is presumed that the length when the annual ring is formed with the relational expression of the length and the scale radius is about 23cm. Moreover, the length when the growth assessed from the upheaval line interval wide is fast is about 13-15cm. The range of length is 18-30cm when the annual ring is formed with Scale method is presumed, and the mode is 23cm. The change in the transparency by which the growth of otolith is accompanied shows the same pattern as changing scale in the upheaval line interval. It is assessed that the Pacific saury has larval and juvenile stands during January-March, and arows to adult through the young and pre-adult stands during April-August when a change in the length composition is seen. Especially, it is thought that growth is fast in May and June. Meanwhile, the middle size group and the small size group grow up and the change in the composition which shifts to the large size group is observed. It is thought that there is generally no big change in the composition after September, and growth stagnates. As for large size group into which the length is divided based on Matsumiya and Tanaka's (1974) methods and the middle and the small size groups, age is thought to be I + and 0+ from the above-mentioned respectively.
2) Reproduction The early peri-nucleolus stage corresponds to about the relation between the development stage of the ovary and the length as chromatin nucleolus stage corresponds to juvenile, and the later peri-nucleolus stage corresponds to almost in young and pre-adult, yolk vesicle stage, and yolk gloubule stage corresponds to the adult. The development style of Pacific saury's ovary egg is an asynchronous oocyte development, and the egg diameter composition of the developing ovary eggs shows a multimodal pattern. It is thought that the eggs which reach the tertiary yolk globule stage develops rapidly, matures, and ovulates when the change in the development stage of the egg is seen. Fecundity is presumed to be almost 1000-3000. The gonado-somatic index of adult females thought to be maturs and egg laying soon is 2.0 or more. Individuals of 2.0 or more appear a lot in February, March, and June, and few in September. The difference by the length of this change pattern was not remarkable.
3) Distribution, movement and migration The larvae are chiefly distributed in the perturbed area in the autumn. Moreover, they are distributed in the subtropical mode-water area outside of the Kuroshio in the winter and in going north warm water of the Kuroshio system in the spring. The larvae and juveniles move north while growing up from the spring to the early summer. They migrate to the Oyashio area during the developmental stage reaching the preadult period. The group with an undeveloped gonad of age I + at the same time also migrates to the Oyashio area. The developing group of the gonad of age I + does not migrate to the Oyashio area at this time, but stays in the perturbed areas, and spawn in the autumn. The fish which migrate from the Oyashio area south in the autumn develop the gonad after assing the Oyashio Front, changes to the egg laying preparation period the growth stage, and after winter, chiefly spawns.
4) Resource structure Situations of the composition of the age, sex ratio and the vertebral number, of the presumed growth curve the reproduction process, parasite rate, etc. suggest division into some groups and living though are when the Pacific saury in the northwest Pacific Ocean belongs to as a whole one system group.
2. Considerations of resource fluctuations
1) Presumption of stock size
The number of larvae was obtained from the number collected for each larval net haul by the area method, the abundance of egg-laying was presumed from its number based on the theoretical formula of the Pacific saury's death curve, the age composition, sex ratio, and the gonad index were assumed to be a parameter, and the stock size according to the age was presumed by so-called the number of eggs method.
2) Change of stock size In the stock size, in 1977 year was 5,600,000 tons and at a high level. It has changed during 1988 afterwards within the range from almost 600,000 to 1,500,000 tons. It is thought that the change of oceanic conditions, food, predator and fishing effort which correspond at a peculiar developmental stage and the life cycle in the process of the development of the life history takes part in the fluctuation of the resource.
3) Relation between the stock size and the catch The catch increases relatively by reinforcing the fishing effort compared with the level of the stock size.

言語

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 63, 号 tnf_k_63_1, p. 1-95, ページ数 95, 発行日 2000-03

出版者

東北海区水産研究所

言語

出版者

Tohoku National Fisheries Researh Institute

言語

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

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北西太平洋におけるサンマの生活史とそれにもとづく資源変動の考察

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