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北洋産DALL'S porpoiseの生態について


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Title: 北洋産DALL'S porpoiseの生態について
Other Titles: On the Ecology of the DALL's Porpoise in Bering Sea and the North Pacific Ocean
Authors: 水江, 一弘 / 吉田, 主基 / 竹村, 暘
Authors (alternative): Mizue, Kazuhiro / Yoshida, Kazumoto / Takemura, Akira
Issue Date: Nov-1966
Publisher: 長崎大学水産学部
Citation: 長崎大学水産学部研究報告, v.21, pp.1-21; 1966
Abstract: As a result of our investigation on the stomach contents of 148 animals and the gonad of 103 animals from among many DALL'S porpoises which had been caught by the Japanese salmon fishing gill nets in the Bering Sea and the North Pacific Ocean in 1964 and 1965, the following characteristics have been ascertained. The sampling period in each year lasted for three months from the latter part of May to the first part of August. 1) The stomach contents of infant porpoises were their mother's milk in all cases; no other food was found; and there was no empty stomach. 2) In this sea area, small marine animals (squid, fish and shrimp) for the food of porpoises were very abundant in this season, but generally the quantity of their stomach contents was not so large. 3) No significant difference was recognized in quantity and kind of stomach contents between male and female, but there was a distinct difference between pregnant and nonpregnant animals. The contents were less in quantity and more polyphagous in the former than in the latter. 4) Squid were very abundant in this sea area in this season, and porpoises ate mostly these squid. Sometimes fish and shrimps were found among the stomach contents but these were very small in quantity in camparison with squid. 5) There was only one sample of red salmon in the investigated stomachs, but it is most likely porpoises do not eat adult salmons as their food. It is not clear whether or not small size salmons in this sea area are caught by porpoises. It is subject to future investigations. 6) As a result of the investigation in 1965, it was clarified that the period of parturition for the porpoises in this sea area is between the latter part of July and the first part of August. 7) It is presumed that the body length of a baby porpoise at the time of parturition is about 100cm. 8) It is believed that the pregnant period of porpoises is less than a year. Fetuses were found in the left uterine cornu in all cases. 9) A sexually mature male is 185cm in body length or more, and three years or more in age. 10) Any perfectly ripe testis was not found in this investigation in spite of many large male samples. It is deemed that the time of copulation came after the period of this investigation. This is also evident from the result of the investigation of the ovaries. There was no difference in weight between the left and right testes. 11) There was no difference in size between the left and right ovaries in the stage of fetus, but since childhood, the left ovary became larger than the other. Ovulation from the left ovary was observed in all cases (83 cases) with the exception of one case. The right ovary was immature in those 83 cases. 12) The corpus luteum projected to the outside of the overy and the size was four or five times as large as that of the ovary. 13) The corpus luteum of ovulation (corpus luteum menstruationis) was not found in this season. This is on account of the fact that the period of this investigation did not fall on the pairing-time of this species. This is also evident from the observation of hystological ovarian sections. 14) With this species, too, the corpus luteum fade away quickly into the ovary when its function terminates and becomes the corpus albicans, but it seems that the corpus albicans in the ovary of this species does not disappear for their whole life as in the case of large whales. 15) Most of the females reach sexual maturity after two full years since their birth. The body length at that time is about 170cm. 16) Most of the vesicular follicles do not ovulate but fade away, and on account of the increase in cells of the follicular epithelium, the liquor folliculi disappears and the follicle becomes hyaline and then disappears. 17) The lutein cells in the corpus luteum disappear quickly after the parturition. 18) The growth curve of DALL'S porpoises drawn from their body length and body weight (Fig. 6) which had been investigated in 1964 and 1965, is shown in Fig. 7. 19) One individual of common porpoise and one individual of BAIRD'S beaked whale were caught by the salmon fishing gill nets in addition to DALL'S porpoises in the season of 1965, and they were investigated. / 1964年,1965年の両年北洋母船式鮭鱒漁業の流し網にかかった多くのDALL'S porpoiseのうち,148頭について胃内容の,103頭について生殖巣の調査を行なった結果,次のことが明らかになった.期間は5月下旬から8月上旬の3ヵ月間である. 1) 稚体の胃内容は総て乳液であり,他の餌は全く発見できなかった.また,空胃は存在しなかった. 2) 本海域はこの時期には餌料生物が非常に豊富であるにもかかわらず,一般に胃内容量は少ない. 3) 雌雄による胃内容の量および種類の差は認められないが,妊娠獣と非妊娠獣では明らかな差があり,前者の方が量は少なく雑食性である. 4) 本海域のこの時期ではイカ類が頗る豊富で本種の主食になっている.胃内容にはこの他にエビ類・雑魚も発見されるが,これらはイカ類に比べて量的に極めて少ない. 5) ベニザケを摂食していた事例が一つあったが,本種は成長した鮭鱒に対して殆んど食害を与えていないと推定される.小型の鮭鱒に対する食害については不明であり,今後の調査に待ちたい. 6) 本海域における本種の分娩時期は7月下旬より8月上旬にかけてである. 7) 本種の分娩体長は100cm前後と推定された. 8) 妊娠期間は1年未満と推察される.胎児はすべて左側の子宮角から発見された. 9) 本種の雄の性的成熟体長は185cm以上であり,満3才以上である. 10) 本調査時期中には完熟精巣は全く発見されず,交尾の時期はこの調査時以後に到来するものと思われる.これは卵巣の調査からもいえる.精巣では左右による重量(成熟度)の差は見られない. 11) 卵巣の大きさは胎児の時は左右の差はないが,幼体以降においては左側の方が他よりも大である.また排卵は1例を除いて総て(83例)左側の卵巣より行なっていた.右側の卵巣は未成熟の状態である. 12) 本種の黄体は卵巣外に突出し,その大きさは卵巣の4~5倍である. 13) 本漁期中には単なる排卵の黄体は全く発見されていない.これはこの漁期が本種交尾の時期以外であるためである.このことは組織学的調査による卵巣の状態からもいえる. 14) 黄体はその機能が終れば急速に卵巣中に収縮して白体となるが,しかし,本種の白体は消失しない. 15) 本種の雌の性的成熟は大部分は生後満2年経過した後である.そしてその時の体長は約170cmである. 16) 卵巣中の胞状卵胞は殆んどがその機能を果さずに収縮する.すなわち卵胞萎縮である.そして卵胞膜細胞の増殖侵入によって卵胞液が消失し,硝子様帯となってその姿を消す. 17) 黄体細胞は分娩後始めて急速に消失する. 18) 漁期中測定した本種の体長・体重(Fig. 6)より成長曲線を描くとFig. 7のごとくなる. 19) 漁期中,鮭鱒流し網には本種の他に小型歯鯨類はネズミイルカ1頭・槌鯨1頭が網にかかり調査された.
URI: http://hdl.handle.net/10069/31459
ISSN: 05471427
Type: Departmental Bulletin Paper
Text Version: publisher
Appears in Collections:第21号

Citable URI : http://hdl.handle.net/10069/31459

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