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北洋鮭鱒漁業の流し網にかかったイルカについて


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Title: 北洋鮭鱒漁業の流し網にかかったイルカについて
Other Titles: On the Porpoises caught by the Salmon Fishing Gill-Net in Bering Sea and the North Pacific Ocean
Authors: 水江, 一弘 / 吉田, 主基
Authors (alternative): Mizue, Kazuhiro / Yoshida, Kazumoto
Issue Date: Oct-1965
Publisher: 長崎大学水産学部
Citation: 長崎大学水産学部研究報告, v.19, pp.1-36; 1965
Abstract: 1) A great number of porpoises had been caught by the Japanese, salmon fishing gill nets in Bering Sea and the North Pacific Ocean except a few northern porpoise whales and minke whales. A salmon fishing fleet had caught more than 1,000 porpoises every year, and 11 Japanese salmon fishing fleets had caught more than 10,000 porpoises. These porpoises have hitherto not been utilized and have been thrown into the sea. 2) The porpoises thus caught belong to one species of the various kinds of the porpoises. Of 54 of them, the body color, body shape, external proportions, skull measurement, number of vertebrae, os costale, cartilago costale and the teeth were investigated, and their food and reproduction behaviors were surmised from their stomach contents and their uroganital organs (i. e. genital organs, mammary gland and fetus). As a result of these investigations, it was found that this species of porpoise is so-called DALL'S porpoise itself which DALL had caught in the adjacent water of. Adakh Is. in 1873 and TRUE had reported as Phocaena dallii TRUE in. 1889. 3) In 1911 ANDREWS found out, in the north-east coast of Japan, a porpoise (what we call "Rikuzen-iruka" in Japanese) and he named this porpoise Phocoenoides truei ANDREWS (TRUE's porpoise). And then he maintained that 'genus Phocaena' which TRUE had indicated in his report should be divided in two groups; 'genus Phocoenoides' should be established newly and Phocaena dallii be displaced by Phocoenoides dalli. The authors. will conform to this opinion. 4) The range in which this species of porpoises were caught is shown in Fig. 1. It seems that they exist in abundance in the sea area more eastern than Long. 175° W., but the Japanese salmon fishing factory ships do not operate in the sea area more eastern than Long. 175° W., so there is no report about this species of porpoises in that place. DALL's porpoise were caught in larger quantities by the salmon fishing gill nets in the adjacent water of the islands along the Aleutian Is'lands and in the east coastal sea of Kamchatka Peninsula than in other areas, and the number of the porpoises caught was in direct proportion to the catch of the salmon. 5) In the case of the adult animales, the body color of these porpoises are deep black except their specific white parts. There is a wide clear white pattern of heart shape from the anus to the umbilicus at the abdominal region (Plate II-5), the tip of the dorsal fin (Plate II-6) and the tail flukes (Plate II-7) are white and then there are many gatherings of the white dots or complicated whitish patterns at the perimeter of the flippers (Plate III-8) and the finny projections (Plate II-7) in the dorsal and ventral margins at the front of the flukes. In the fetus (Plate I-2) or the infant stage (Plate I-3), there is no white part except the only white pattern at the abdominal region, and the animal in childhood-one year after the birth, has white parts at the abdominal region and the tip of the dorsal fin. The abdominal white part is indistinct to some extent until they reach adult. 6) The body shape is in fusiform, stout and closely resembles to the Rikuzen-iruka (Phocoenoides truei) or Ishi-iruka (Phocoenoides dalli?) which live in the north-east sea area of Japan. There is no snout, but the tip of the mouth becomes sharp a little and the lower jaw projects slightly than the upper one (Plate IV-13, 14, 15). And there is the prominent finny ridge, at the dorsal and ventral margins in the front of the tail flukes, which porpoise has had since the fetus and the infant stage (Plate I-2, 3, Plate III-9), and in the adult stage this dorsal project is exterme (Plate III-10). 7) The values of the external proportions are shown in Table 2. The head of this porpoise is smaller than those of other species, and the growth of the body length of this species is due to the growth of the abdominal part as in the case of Neomeris phocaenoides. 8) The body weight of about 47 animals of this species containing three fetus, was measured, and the relation between the body length and weight of this secies, in summer, in this sea area is as follows. W=L²·³⁴¹×10⁻⁴·¹º⁶ 9) The values of the skull measurement are shown in Table 3. The space between both orbits of this skull is broad (Plate V-16) and the dorsal face in the front of the orbits of skull is flat in general (Plate VI-18, 19). The width of the base of the snout is broad (Plate V-17), the nares are very large and the fore part of the nares on os incisivum rises extremely (Plate VI-19). Os nasales are situated more forward than those of other porpoises and they have a projection respectively in the outer side of the bones (Plate VII-21). Both os pterygoides separate from each other and os palatinums exist, occupying in large space, between them as we find in the case of Neomeris phocaenoides (Plate V-17). 10) The number of vertebrae of this species is shown in Table 4 and they are most numerous as compared with other porpoises and dolphins. All the cervical vertebrae adhere one another to all specimens. 11) The number of os costales is shown in Table 5. Ist.-5th. of the left and right cartilago costalis are connected with the sternum by the cartilage. The number of cartilago costalis which does not connect with the sternum is shown in Table 6. And then the number of os costales which are not accompanied by cartilago costalis is shown in Table 7. 12) The teeth are very small and slender in the case of this porpoise; the tips of the teeth are sharp and their shape is various. The exposed part of the teeth is slightly shown and when we feel with our hand upon the teeth from the outside, the tip of the teeth can not be touched by our hand as the gingiba is higher than the tips of the teeth (Plate IV-13). The number of teeth is shown in Table 8. The number of teeth in the lower jaw is more than those in the upper jaw. 13) As a result of the investigation of the stomach contents of this porpoise in this sea area, it was found that they take the squid mainly; and the shrimps and many bones of fish were found in their stomachs, but it will made clear by further investigations to be made in future, whether the salmon in this sea area will suffer considerable damage because of these porpoises which eat them as th,ir food and as to the degree of the damage if it happens. From the fact that the stomach contents of this porpoise concurred, in general, with those of the salmon which had been caught at the same time, it is supposed that they migrate seeking for the food with the salmon. And then, as the porpoise attacks the salmon caught in the net, being entangled by it and suffocated, it is presumed that many porpoises were caught by the salmon gill net. 14) The sex ratio of the investigated porpoises is 26♀/28♂. It seems that this species is delivered of its cub in this sea area between the middle of July and the first ten day of August, and in the case of the southern groups in the sea area we studied, the season of the parturition is earlier to some extent than in the case of the northern groups. Concluding from the largest fetus and the smallest infant of this porpoise, it is supposed that the body length of the fetus at the parturition is 85-90cm. All fetus were found in the left uterine cornu. In the female animals immediately after the parturition, the evidence of it was noticed at the left uterine cornu and a corpus luteum existed in the ovary; the graafian follicles developed at the left ovary in the resting stage of the adult female animals and the right ovary was immature without exception in this investigation. 15) Phocoenoides truei and especially P. dalli (?) which live in the north-east sea area of Japan resemble closely to this porpoise. But the authors regret that there are few data about these porpoise and those of the adjacent water of North America, so the authors can not compare these values with those of other sea areas and can not discuss about the situation of the classification of these porpoises.
Description: 26頁は白紙
URI: http://hdl.handle.net/10069/31536
ISSN: 05471427
Type: Departmental Bulletin Paper
Text Version: publisher
Appears in Collections:第19号

Citable URI : http://hdl.handle.net/10069/31536

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