202 



Fishery Bulletin 104(2) 



was a concomitant delay of two to three months in 

 this increase. 



Catch of YFT in relation to recruitment 



Recruitment explains most of the YFT catch fluctuations 

 in relation to El Nino events at the entrance of the Gulf of 

 California. A recurrent pattern in the time-series of the 

 catch revealed a peak of catch fourteen ( 1993 1 to twelve 

 (1999) months following an El Nino event. A similar 

 result has been observed in a cross-correlation between 

 the Southern Oscillation index (SOI) and the long-line 

 series of catch data for yellowfin tuna; a positive correla- 

 tion was found in the eastern Pacific region after a lag 

 of fourteen months (LehodeyM. This finding supports the 

 hypothesis of a recruitment base (age-effect) for yellowfin 

 because at 14 months YFT reach 75 cm, corresponding to 

 the first age class recruited to the long-line fishery. These 

 results are also consistent with those from previous 

 analyses of time-series of catches of YFT in the eastern 

 Pacific, namely by Joseph and Miller^ and the IATTC-. 

 Therefore, recruitment can be the major explanation of 

 the YFT catch fluctuations in relation to El Niiio events 

 at the entrance of the Gulf of California. 



been observed in the central Western Pacific for the 

 long-line fishery (Lu et al., 2001). 



Forecasting catch within the study area may give us 

 the ability to reliably develop predictions of catch fol- 

 lowing El Nifio or La Niiia events. 



Acknowledgments 



The first author was a CONACYT grant holder for the 

 duration of his doctoral studies at CIBNOR (Reg. 60997). 

 The Universidad de Colima and PROMEP also supported 

 our research effort. The research project was supported 

 by a CONACYT grant (990107004). We are grateful to 

 the ATUN project (CICIMAR-IPN) for providing the 

 capture data. The third author is a SNI grant holder 

 and wishes to acknowledge the support of the Oceanol- 

 ogy Division of CICESE and of CICESE's campus at Baja 

 California Sur. We are grateful for the critical analysis 

 and suggestions from two anonymous reviewers and the 

 scientific editor. 



Literature cited 



Catch distribution of YFT related to ENSO episodes 



For the long-line fishery in the tropical Pacific Ocean, 

 areas with significant higher hook rates of YFT during 

 El Nino years are located east of 150'"W within tropical 

 waters of the central eastern Pacific (Lu et al., 2001). 

 Conversely, higher hook rates occur during La Nina epi- 

 sodes in areas where SSTs rise during El Nifio events. 

 These two findings may provide two possible reasons 

 for the change in hook rates; the expansion of optimal 

 habitat and the change in vulnerability of the resource 

 to the fishing gear during the ENSO episodes. 



Conclusions 



At the entrance of the Gulf of California, an El Nino 

 event is associated with an increase in the purse-seine 

 catch of YFT after two to three months, when SSTAs 

 reach the study area. Similarly, this increase is delayed 

 three to four months after the onset of El Niiio at the 

 equator. 



A positive correlation of El Nifio on YFT catch at 

 the entrance of the Gulf of California after a twelve 

 to fourteen month delay supports the hypothesis that 

 the ENSO affects recruitment of YFT. This correlation 

 seems to be independent of the thermal structure dur- 

 ing the recruitment phase. In 1993, normal conditions 

 in SST were present, whileas in 1999 La Niiia was 

 observed. 



A northward displacement of YFT seems to occur at 

 the entrance of the Gulf of California twelve to fourteen 

 months after El Nino events. Lower catches in southern 

 latitudes were recorded, whereas higher catches were 

 recorded in northern latitudes. Similar results have 



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