fishermen. During the last 20 years the catch 

 has been mostly fish of 25 - 30 lb. or less. 

 Since 1958, some large bluefin (>100 lb.) have 

 reappeared in the catch. California bluefinmay 

 inhabit either warm, high-saline water, such as 

 is normally occupied by yellowfin, or the cold, 

 low-saline water characteristically inhabited by 

 albacore, but they occur mostly in water with 

 temperature -salinity characteristics intermedi- 

 ate betweenthese two. In years when ocean tern - 

 peratures are unusually warm, the California 

 bluefin ranges hundreds of miles farther north. 

 It was agreed that a cause -and -effect relation- 

 ship between distribution and ocean temper- 

 ature should not be postulated without further 

 investigation. 



It was stated that bluefin leave the 

 California coastal area for spawning, since there 



is an absence of sexually mature adults, eggs, 

 and larvae in this area. H. Nakamura presented 

 evidence for a possible continuous distribution 

 of bluefin across the Pacific. 



To further our understanding of tuna 

 distribution, it was felt that increased emphasis 

 should be given to tagging of small tunas in the 

 western and North Pacific, of albacore off South 

 America, and of southern Australian bluefin. 

 The design of exploratory fishing surveys uti- 

 lizing special equipment was recommended. We 

 can expect further knowledge to result from 

 studies on migration, subpopulations , behavior, 

 and oceanography, all of which relate to 

 distribution. 



Migrations 



Discussion Leader - Tamio Otsu 

 Rapporteur - Eugene L. Nakamura 



Reference: Papers No. 



II - 1. Otsu, T., and R. N. Uchida - A model of the migration of albacore in the North 

 Pacific Ocean 



2. Clemens, H. B. - Migration, age and growth, and spawning studies of the North 

 Pacific albacore (Thunnus germo) 



A model was presented of the migration 

 of albacore in the North Pacific Ocean, based on 

 tag recovery data, age and growth data, and dis- 

 tribution and size frequency data from the three 

 major albacore fisheries: the Japanese live - 

 bait fishery, the Japanese longline fishery, and 

 the American west coast trolling and live -bait 

 fishery. This model is consistent with the hy- 

 pothesis that there is a single population of alba- 

 core throughout the North Pacific Ocean. 



Discussion of the albacore tagging data 

 brought forth remarks that young bluefin in 

 Australian waters ought to be tagged to see if 

 they would appear in the Japanese longline fish- 

 ery in equatorial waters. Agreement was 

 expressed by others with further remarks con- 

 cerning the desirability of tagging the young of 

 all species of tuna to help solve distributional, 

 growth, and taxonomic problems of the various 

 species . 



Further discussion about small albacore 

 centered around the 35 -cm. modal group. It was 

 stressed that one should be aware of the fact that 

 even though 35-cm. fish are present they may 



not be fished for economic reasons, particularly 

 if larger fish are available. 



A suggestion was made that in viewof the 

 amount of information available from the various 

 laboratories studying albacore, a joint effort 

 should be made to define more clearly the prob- 

 lem of assigning absolute ages to modal groups. 



The view was expressed that there may 

 be some danger in assuming that recruitment 

 occurs only in the eastern Pacific. There was 

 general agreement that the major spawning area 

 is in subtropical waters, but which way do the 

 newly hatched fish go? What size are they when 

 they enter the postulated migratory routes? At- 

 tention should be directed toward the smaller 

 fish, particularly the 35-cm. modal group. 

 These fish have been reported in the area of the 

 Japanese live -bait fishery by fishermen who do 

 not catch them for economic reasons. So per- 

 haps it may be better to hypothesize that recruit- 

 ment occurs in both the Japanese and American 

 fisheries. Plans are being made by the Japanese 

 to use special gear for catching these small fish 

 in the future. 



