238 EIGHTH PACIFIC SCIENCE CONGRESS 



some much weaker animals quite indifferent to the food habits of the 

 predators [planktonic crustaceans — Tetraodontidae — Trichiurus (19h. 

 20 min. Sept. 17, 1950), planktonic crustaceans — Engrcndis of Shirasu 

 stage— Trichiurus (3h. 25 min. Sept. 18, 1950)]. During the observations 

 I have also recorded the order of arrival of main lamp-animals near the 

 lamp. The order of animals, determined by the mode of frequency, 

 is as follows: planktonic crustaceans — Engraulis of Shirasu stage — 

 Atherina — Cypselurus — Engraulis — Pempheris — Stolephorus — Sphy- 

 raena — squids — Carangidae — Trichiurus. Squids contain some small 

 individuals which come to the light early and are considered to be- 

 long to the prey group. The order of arrival of squids as solely the ter- 

 tiary predators is much later. Although Sphyraena seems to come to 

 the light earlier than carangids in the order determined by the mode 

 of frequency: Sphyraena — squids — Carangidae — Trichiurus, in actual 

 cases it and Trichiurus assemble to the light last. Whenever they visited 

 the light relatively earlier, no other animals could be expected under 

 the lamp after their arrival. Actually there was no case, in that the 

 carangid came to the light later than squids, Sphyraena and Trichiurus. 

 From these facts the order of arrival near the light may be determined 

 as follows: Carangidae — Sphyraena — squids — Trichiurus. Thus, the 

 order of arrival near the light is quite parallel to the order of food 

 rank and the spatial arrangement mentioned previously. 



Successional changes are strongly affected by the dispersing acti- 

 vity and the order of arrival; those two facts are also related closely 

 with the rank of animals in the lamp-community described previously. 



B. Predators absent. 



At Murotsu, about 35 miles west of Kobe, the gray rock cods 

 (Sebastodes inermis) are gathered by scattered bait and angled up in the 

 daytime. At night, the acetylene lamp is placed near the rock not far 

 from the coast and the fishes gather around the lamp to eat the zoo- 

 plankton and Shirasu assembling around the lamp. Then fishermen 

 angle for these fishes. 



In the latter case, it has been said that the more preys are assem- 

 bled around the lamp the more fishes are caught. The amount of 

 conger leptocepharus in preys is considered one of the key factors. Ac- 

 tually the stomach of the angled gray rock cod is filled with the zoo- 

 plankton and fry which are considered to be assembled to the lamp. 

 I have been told that the fishes hardly assemble in the daytime near 

 the rock where the lamp is put at night, even if scattered baits are 

 placed in the water. It is clear that the prey plays a significant role 

 and there are no predators of the fishes in the present case. 



