The statement was then made that per- 

 haps discussions of recruitment involve a se- 

 mantic problem. One use means recruitment 

 into the fishery while the other means recruit- 

 ment into the temperate North Pacific Ocean. 



The question of tagging small fish arose 

 again. It seems desirable to tag small albacore. 

 It was suggested that the salmon investigators 

 might be encountering small albacore in their 

 gill nets. However, it was believed that the 

 mesh sizes used for salmon were too big to 

 catch small albacore. 



Serological evidence supports the hy- 

 pothesis that a single reproductive population of 

 albacore exists in the North Pacific Ocean. 



The subject of depth of albacore occur- 

 rence was discussed next. In both the Japanese 

 live -bait fishery and the American fishery, the 

 fish are caught at the surface. In the longline 

 fishery, the albacore are caught with gear fish- 

 ing down to 100 meters . The depth of occurrence 

 may be associated with the depth of the mixed 

 layer. Japanese longline fishermen adjust the 

 depths of the hooks depending upon the area 

 fished. 



In connection with depth of occurrence, 

 the suggestion was made to further develop the 

 idea of a depth gauge which could be attached 

 directly to the fish. If a miniature type of bathy- 

 thermograph could be developed, it could help 

 solve problems of vertical distribution. Such 

 depth gauges, which must be inexpensive, small, 

 and calibrated after recovery, were worked upon 

 by Bureauof Commercial Fisheries technicians 

 at Seattle, but lack of interest and research 

 funds brought an end to the project. 



A method that has been used in Japan to 

 determine the depth of fish occurrence was de- 

 scribed. The gear consisted of a float attached 

 to each branch line. It was implied that the fish 

 could not have been caught at a depth deeper 

 than the length of the line. In the Celebes Sea, 

 yellowfin were caught as deep as 160 m. , but 

 most were caught at 100 m. Marlin catches were 

 best at 70 to 80 m. , and shark catches at 30 m. 

 However, the work of gear handling was increased 

 greatly so that not as many units could be fished 

 as normally. 



The use of echo sounders for determining 

 hook depths was mentioned, and a design for a 

 sonic reflector tag for skipjack was described. 



Vertical distribution of tuna in relation 

 to oceanographic factors was also discussed, 



such factors being internal waves, the deep scat- 

 tering layer, and temperature discontinuities. 



It was pointed out that there was basic 

 agreement between the two reference papers and 

 that the major difference was in the assignment 

 of absolute ages to the various modal groups. 

 Another difference was that Clemens' paper pos- 

 tulated that some albacore of all sizes remain 

 in the central Pacific without migrating either 

 eastward or westward. The paper by Otsu and 

 Uchida does not so postulate, although available 

 data would tend to support Clemens. 



Clemens' estimation of albacore age is 

 1 year less than that of Otsu and Uchida. The 

 possibility of the difference being due to a differ- 

 ent assumed spawning season was expressed. 

 Clemens believes that the youngest fish entering 

 the American fishery are really about 15 or 16 

 months old. In addition to other data, Clemens 

 read scales from near the caudal peduncle to 

 estimate age. Slides were shown of albacore 

 scales from the peduncle of a 59-cm. fish which 

 had one annulus, a 69 -cm. fish with two annuli, 

 and a 75-cm. fish with three annuli. It was 

 stated that scale readings of albacore in 

 Japan were in agreement with the California 

 studies. The opinion was also expressed that 

 because scales in the peduncular area are the 

 last to develop in a young fish, the first annulus 

 may be so compact and small in radius that it may 

 be overlooked. A comparison was made of the 

 albacore growth curves of Clemens and of Otsu, 

 and both are nearly identical for fish sizes above 

 50 cm. A statement was made that in the Atlantic 

 yellowfin and bluefin the first year's growth is 

 in the neighborhood of 30 cm. 



The discussion then turned to triggering 

 mechanisms for migration. Two areas of search 

 for this triggering mechanism were suggested: 

 in the environment and within the organism. It 

 was then suggested that the two probably inter- 

 act, that an environmental mechanism (extrin- 

 sic factor) interacts with an internal mechanism 

 (intrinsic factor). That extrinsic factors may 

 be temperature or length of daylight was dis- 

 cussed. An example of the importance of length 

 of daylight was given for the maturation of the 

 ayu in Japan. It was suggested that the intrinsic 

 factor is possibly associated with the endocrine 

 system, as has been shown in salmonids. 



The final discussion involved the use of 

 commercial landings as indicators of presence 

 or absence of albacore. It was pointed out that 

 lack of commercial landings need not mean the 

 absence of albacore, but rather the lack of en- 

 counter between fishermen and fish, whether it 

 be due to inclement weather or something else. 



