Observation! on the skipjack fishing grounds 



Last year (1923) I mas able to assemble and publish various items concerning 

 the tunas and bonitos, which I have been studying for the past ten years or more* 

 This year, with the assistance of the Kelmeikai Foundation, I have continued these 

 studies. In May I made a field trip to Kagoshima Prefecture and, through the 

 kindness of the Prefectural Fisheries Experiment Station, I was able to travel 

 aboard the research vessel Shbyo Maru to the islands of Kuchinoshima, Nakanoshima, 

 Kogaja, Gaja, Suwase, Taira, Akuseki, Kotakara, Takara, and Yokoate, which lie be- 

 tween Yakushima C30°20'N, 130°30'E]and Amami Oshima [28°15'N, 129°20'E], and saw 

 the actual conditions on the skipjack grounds of the area, which extend for about 

 100 miles from north to south and about 60 miles from east tc west. Since the 

 materials which I obtained at that time and those which were previously collected 

 for me by Mr. Gisuke Umemoto aboard the same vessel are important to the knowledge 

 of the life histories of the skipjack and other pelagic fishes. I am going to 

 gradually assemble and make available these data, beginning with those parts the 

 study of which has already been completed. 



Skipjack [Katsuwonus pelamls] 



I took along with me a specially constructed net for collecting larval and 

 juvenile fish, but there were few opportunities to try it and I was regrettably 

 unable to learn whether or not it is suitable. Fish eggs and larval fishes were 

 collected with a small net, but it is not known to what species these belong. This 

 is because I have never seen ripe skipjack eggs and do not know the characteristics 

 of newly-hatched larval skipjack. 



Among the material which I obtained the specimens which can be recognized with 

 certainty to be skipjack were recovered from the bellies of the parent skipjack and 

 yellowfin (most of them being juveniles). These fish congregated around reefs 

 with depths of over 50 meters and water temperatures of about 25° and fed on the 

 young of various pelagic fishes, called collectively koma.lako by the fishermen, 

 which are abundant in such areas at that season. It is thought that these young 

 fishes, and particularly the young skipjack, are most plentiful in the stomachs in 

 the forenoon. There are quite a few fresh specimens in the koma.lako if it is re- 

 moved from the stomachs immediately after the fish are captured. If they remain 

 for long in the stomachs, the skin is digested and the surface of the flesh also 

 begins to be digested, but even in such cases it is possible to distinguish tunas 

 and bonitos from other fishes by the appearance of the dark red tissue along the 

 sides, and identification is even more certain if the flesh is removed so that the 

 vertebral column can be seen. Five or six juvenile skipjack are sometimes found 

 in one fish, and judging from this it appears that these juveniles are present in 

 some abundance, however, when this is compared with the appearance of 20 or 30 

 juveniles of Prlonurus spp. in one stomach, it is indeed a very small number. 

 Probably this is because the Prlonurus are slow in their movements while the skip- 

 jack are quick. 



The following is a list of the juvenile skipjack which have been collected. 

 Date Length Location 



May 16 

 May 19 

 May 19 



May 21 

 May 21 

 May 21 

 early June 



58 mm 

 60 mm 

 80 mm 

 63 mm 

 83 mm 

 85 mm 

 120 mm 



Nakasone [28°10 , N, 129°15 , e] 



Nakanoshima [29° 51 *N, 129° 52" E] 



Nakanoshima 



Gonsone [29°47% 129°25 , E] 



Gonsone 



Gonsone 



