A comparison of length-frequency distribu- 

 tions taken during the third quarter of the year 

 by the Hawaiian and eastern Pacific fishery pro- 

 vides further clues to the origin of skipjack 

 caught in the Hawaiian fishery. A similarity in 

 size distribution exists between the small-size 

 group of Hawaiian and of eastern Pacific fish 

 for 2 of 3 years for which data are available. 

 This similarity in size could be indicative of a 

 common origin for eastern Pacific and the small- 

 size group Hawaiian fish. By hypothesis the 

 eastern Pacific fish originate in the central Pa- 

 cific; therefore, the concept of a common origin 

 suggests that those taken in Hawaiian waters 

 also originate in the equatorial central Pacific. 

 The lack of apparent similarities between third 

 quarter length-frequencies of Hawaiian and east- 

 ern Pacific fish during the third year for which 

 data have been published is interpreted as an 

 environmentally induced failure of equatorial 

 central Pacific skipjack to enter the Hawaiian 

 Zone during this year. 



A consideration of various features of the 

 biology of the skipjack taken by the Hawaiian 

 fishery yields no immediately discernible con- 

 clusion regarding the origin of those skipjack 

 taken in the Hawaiian Zone. It seems fairly 

 evident, however, that a likely hypothesis would 

 suggest that one of the two subpopulations that 

 enter the Hawaiian fishery originates in equa- 

 torial waters of the central Pacific and is com- 

 prised of fish that make up the bulk of the season 

 catch. The magnitude of the season catch may 

 be related to the physical environment, but it is 

 likely that dynamic features of the skipjack popu- 

 lations are also important. 



CONCLUSIONS 



The purposes of the hypotheses presented in 

 this paper were to assemble data pertinent to 

 understanding the movements of skipjack tuna in 

 the central and eastern Pacific and to provide a 

 guide for future studies. The need for more 

 evidence on the problems of the origin and move- 

 ment of skipjack tuna is evident. The accumula- 

 tion of this evidence should be based on a consid- 

 eration of alternative sets of hypotheses, a sub- 

 stantiation of the assertions made in this paper, 

 and the design of critical experiments to test the 

 hypotheses. 



In considering sets of hypotheses other than 

 those proposed in this paper it is important to 

 note that the conceptual division of the central 

 Pacific into three zones of origin puts immediate 

 constraint upon the nature of solutions. Should 

 the central Pacific be considered as a single 

 zone (one huge population of skipjack that extends 



from the Hawaiian Islands in the north to the 

 Tuamotu Archipelago in the south), as two zones 

 (a northern and southern zone, both or only one 

 contributing to the eastern Pacific fishery), or 

 finally as many discrete zones (each contributing 

 variable proportions of fish to the eastern Pacific 

 fishery), then the nature of the hypotheses based 

 on these considerations might be different than 

 that of the three-zone concept. A consideration 

 of these alternatives and several others has, 

 however , continued to suggest that the three-zone 

 approach presented in this paper is most con- 

 sonant with the evidence as it is now available . 

 When new and pertinent data are acquired, then 

 it is possible that alternatives will be accepted. 



Some of the assertions made in this paper 

 need to be substantiated. Perhaps the weakest 

 assertion involves the exclusion of Marquesas 

 Zone fish from the Central and South American 

 fishery area. The temporal-spatial distribution 

 of skipjack larvae certainly needs to be studied 

 more intensively. One of the more perplexing 

 features of the evidence is the large numbers of 

 immunogenetic ally distinct groups that have been 

 identified. What are the isolating mechanisms? 



Finally, which experiments provide critical 

 tests of the hypotheses? In general, studies of 

 larval and juvenile skipjack are indicated since 

 these studies may provide clues to the year class 

 strength phenomena mentioned earlier in this 

 paper , elucidate isolating mechanisms, and pro- 

 vide samples for subpopulation studies. More 

 specifically an experiment to test the hypotheses 

 is based on the definition of a critical area. This 

 critical area lies along a line between the Hawai- 

 ian Islands, the Line Islands, the Marquesas 

 Islands, and the Tuamotu Archipelago. Juvenile 

 skipjack (since adult skipjack appear to be un- 

 available to capture for some interval prior to 

 spawning; samples of juvenile skipjack are more 

 likely to be from a single genetic pool than the 

 adults) should be taken along this critical area, 

 and their immunogenetic affinities determined 

 with already developed reagents. The immuno- 

 genetic affinities of the eastern Pacific adoles- 

 cent skipjack could then be compared with central 

 Pacific samples to determine the loci of their 

 origin. The conduct of this research will pro- 

 vide added benefits by substantiating various 

 assertions and providing new information on the 

 temporal-spatial abundance of larval and juvenile 

 skipjack. 



SUMMARY 



A set of hypotheses has been generated to ac- 

 count for the origin and movement of exploited 

 skipjack in the eastern and central Pacific Ocean. 



17 



