Tagging in the eastern Pacific . --Most skipjack 

 tagging in the eastern Pacific has been under- 

 taken by the lATTC. Tag recoveries from skip- 

 jack tagged in the eastern Pacific show essential- 

 ly two patterns of movement: a pattern that 

 seems typical for skipjack tagged to the north of 

 the Gulf of Tehuantepec and another pattern for 

 those to the south of this area. Interchange of 

 tagged fish in the north-south direction across 

 the Gulf of Tehuantepec (lat. 15° N.) has not yet 

 been reported. 



In the northern region, studies by the Califor- 

 nia Division of Fish and Game (Blunt and Messer- 

 smith, 1960) have indicated, with limited data, 

 that there is northward movement of skipjack in 

 May and June, northward and southward move- 

 ment in July, and southerly movement in Septem- 

 ber. Schaefer, Chatwin, and Broadhead (1961), 

 with large numbers of tag returns, have shown 

 there are essentially no interarea movements 

 among the lATTC statistical areas north of the 

 Gulf of Tehuantepec. 



In the southern region, there appears to be 

 relatively greater coastwise movement than in 

 the northern region. Blunt and Messersmith 

 (1960) have shown interchange between the Four- 

 teen Fathom Bank (long. 80° W., lat. 9° S.) and 

 the Gulf of Guayaquil (long. 80° W., lat. 3° S.). 

 More detailed studies by lATTC (Schaefer et al., 

 1961) have shown interchange among the regions 

 off Colombia, Ecuador, and Peru. The fish 

 seemed to move toward the Fourteen Fathom 

 Bank in the summer and away from it in the 

 winter. These authors also give data which indi- 

 cate that skipjack marked off Central America 

 may be recovered in South American fisheries. 



Long distance tag recoveries . --To date three 

 eastern Pacific tagged skipjack have been recov- 

 ered in the central Pacific (fig. 9). The two re- 

 coveries in Hawaiian waters were of fish tagged 

 in the spring and fall. The skipjack recovered 

 in equatorial waters was tagged in the winter, 

 was at large for a shorter period of time, and 

 was smaller than the two tagged fish recovered 

 in Hawaiian waters. 



These three recoveries present problems of 

 interpretation. How valid are inferences regard- 

 ing the movements of large numbers of fish based 

 on a few tag returns? To provide some tangibility 

 for this question, the probabilities of recovering 

 a skipjack from a region different from that in 

 which it was tagged should be considered. This, 

 however , requires a discussion of various satel- 

 lite problems such as the distribution of fishing 

 effort on tagged fish, tagging mortalities, the 

 distribution of tagged fish among untagged fish. 



etc. Many aspects of these problems have been 

 discussed in lATTC publications (e.g., Schaefer 

 etal., 1961, Barrett and Connor, 1962). I cannot 

 evaluate all aspects of these problems. Further- 

 more, many of the data necessary for such an 

 evaluation are unattainable with available tech- 

 niques. Therefore, in this study, the probabili- 

 ties of capturing a tagged interregional-migrant 

 skipjack can only be appraised in a gross and 

 qualitative fashion. 



LONG RANGE TAG UCOVERIES OF SKIPJACK 



■^SAN fX.4NCJSC0 

 ~J.OS ANGELES 



JUNE 19U 

 77 CM. 



«UG.1962 

 78 CM. 



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APR. 1H3 y 

 70 CM.^- 



160- "CHRISTMAS! 



Figure 9. --Schematic representation of three 

 long-distance recoveries of tagged skipjack 

 showing time of tagging, time out, time of 

 recovery, and size. These fish were tagged 

 by lATTC. 



The likelihood of recovering a tagged interre- 

 gional-migrant skipjack is dependent on, among 

 other things, the amount of effective fishing effort 

 expended for skipjack in the region of potential 

 recapture. A fairly intensive (for the central 

 Pacific) skipjackfishery exists in the immediate 

 vicinity of the Hawaiian Islands; in other areas 

 of the central Pacific, however, relatively few 

 skipjack are taken. Therefore, the recovery of 

 an eastern Pacific tagged skipjack in the equa- 

 torial central Pacific may appear more likely to 

 represent a large movement of fish than the two 

 Hawaii recoveries. Of the several thousand 

 skipjack tagged in Hawaiian waters during 1957 

 and 1958 none have been recovered in the eastern 

 Pacific fishery. 



Prediction of Hawaiian Skipjack Catch 



Seckel and Waldron (1960) have derived an 

 index which predicts the magnitude of the annual 

 catch of skipjack tuna in the Hawaiian fishery. 

 In essence it forecasts the magnitude of the sum- 

 mer catch (June, July, and August) because a 

 considerable proportion of the Hawaiian catch is 

 taken during the summer. The index itself is 

 based on the time during January, February, or 

 March when the sea-surface temperature off 

 Oahu, Hawaii, changes from cooling to warming. 

 The prediction states that the annual skipjack 

 catch will be above average when the shift from 



10 



