jack tuna from January through April was between 300,000 

 and 800.000 pounds per month. Then in May the catch 

 increased to an estimated 3.5 million pounds and in June 

 was 2.3 million pounds. For the first 4 months of the year 

 average salinities at Koko Head were about 34.99 ",,,,. drop- 

 ping- to 34.65 Villi in May and June. 



On the basis of previously established criteria, the waters 

 changed from what is designated as an unfavorable type 

 in April to a favorable type in May. From the weekly 

 landings and the biweekly salinity samples one can see that 

 the change must have occurred about May 5. The salinity 

 was 34.99 Vim on May 4, dropped to 34.69 ",,„ on May 7 and 

 34.53 ",„, on May 11. For the 7-day period ending on May 3, 

 the estimated Oahu landings were 130,000 pounds, for the 

 7-day period ending May 10, they were 510,000 pounds. 



This correlation supports the hypothesis that water type 

 is important in the distribution of skipjack. It should be 

 emphasized, however, that the correlation is between type of 

 water, of which the salinity is merely an inde.x, and skipjack 

 catch — not between salinity itself and skipjack catch. The 

 decline in the catch rate in June, when salinity remained 

 low, shows that other factors also affect the availability of 

 skipjack. 



Skipjack Hypotheses 

 Theoretical studies of the origin of the skipjack caught 

 by the Californian and Hawaiian fleets may seem remote 

 from the immediate interests of the fishery. Yet until it is 

 known where and when the fish are spawned and in what 

 quantities it will be mosi. difficult to arrive at valid sugges- 

 tions for rational management of the resource. Since fishery 

 scientists, dealing with matters that vitally affect major 

 industries and international relations, only cautiously put 

 forward general theories on the basis of evidence not 

 wholly and repeatedly substantiated, there exists no gen- 

 erally accepted "skipjack theory." This reporting period, 

 however, has seen the publication of a scientific paper by 



Brian J. Roth.schild that considers all of the available data 

 on the skipjack tuna and advances a set of interlinked 

 hypotheses to explain some of the enigmas of the fluctua- 

 tions of the skipjack catch. These hypotheses are not yet 

 a theory, but constitute a bold and significant first step 

 toward one, and almost all research on the skipjack in the 

 next few years will need to take them into consideration. 



In brief, on the evidence of data on spawning, size distri- 

 bution, movements, and gonad indices, Rothschild hypo- 

 thesizes that the small skipjack that make up the bulk of 

 the eastern Pacific catch are spawned not in those waters 

 but somewhere in the central Pacific and that they immi- 

 grate to the shores of the Americas at an early age, stay 



jmm 



FIGVRE 12. The ai-rhal of water of lower »altnitv at 

 Oahu rail signal g<»od skipjack catches. Here are shown the 

 average nionthlv salinity values at Koko Head from January 

 through June 1965 (the line) and estimated a>erage skip- 

 jack catches (bars). Note that as salinitv dropped. es|i. 

 mated skipjack catches increased. 



17 



