Torres-Orozco et al Variation in catches of Thunnus albacores related to El Niho-Southern Oscillation events 



199 



base (IRI'). The SST fields were blended from 

 ship, buoy, and bias-corrected satellite data. A 

 description of this procedure can be found in 

 Reynolds and Smith (1994). SSTA data for El 

 Niiio region 3 (NIN03, from 150°W to 90°W 

 and from 5°N to 5°S) were obtained from Cli- 

 mate Prediction Center databases (CPC'). 



Yellowfin tuna catch data were obtained 

 from the database of the ATUN (tuna) Project 

 of CICIMAR (the Interdisciplinary Research 

 Center of Marine Science of the National 

 Polytechnic Institute in La Paz, Mexico). This 

 database has information on daily fishing ac- 

 tivities for about 80% of the Mexican purse- 

 seine fleet operating in the eastern Pacific. 

 The data used in the present study include 

 carrying capacity, catch-by-species, location, 

 and school type (YFT associated with dol- 

 phins; YFT associated with floating objects; 

 and free-swimming YFT), from 1990 to 1999, 

 comprising 11,690 records. Total distribution 

 of the sets made by the Mexican purse-seine 

 fleet from 1990 to 1999 at the entrance of the 

 Gulf of California is shown in Figure 1. 



Interannual variation 



In order to study annual variation, total 

 catches of YFT of the purse-seine fleet within 

 the study area were accumulated by year. 

 A cross-correlation analysis was applied to 

 obtain information on lags between SST 

 anomalies and YFT catches. 



Latitudinal stratification 



In order to analyze the latitudinal catch 

 variation of YFT within the study area, 

 catch data for the period 1990-99 were 

 accumulated in six latitudinal bands of one 

 degree from 18°N to 24°N at the entrance of 

 the Gulf of California. Longitudinal limits 

 extended from the coastal line of the Mexi- 

 can continent (from 104°W to 112°W). 



24' N I 



23' N 



22"N 



2r'N 



20"N 



19' N 



t. . . - . .......Csivv. J.'.: ■• i 



114"W 



108°W 



•■:i;;ii^iC-r:^ 



\rd--^ ■'■'■-••:••', .•■•'!••: ' .Itf- v-fftlH 



i 



112 W now 108 W 106 W 104°W 



Figure 1 



Total distribution of the sets made by the Mexican purse-seine fleet 

 during 1990 to 1999 at the entrance to the Gulf of California. Catch 

 data for yellowfin tuna {Thunnus albacares) were obtained from the 

 CICIMAR (the Interdisciplinary Research Center of Marine Science 

 of the National Polytechnic Institute in La Paz, Mexico). 



« 20 



1994 1995 



Year 



1996 



Total 

 1990- 



Figure 2 



catch for yellowfin tuna [Thunnus albacares) by year during 

 -99 in the study area. 



Results 



Interannual variation in YFT catch 



The catch of YFT in the study area showed high inter- 

 annual variation (Fig. 2). This high variation showed 



■■' IRI (International Research Institute for climate prediction). 

 2002. Sea surface temperature anomaly data. Website: 

 http://ingrid.ldgo.columbia.edU/SOURCES/.NOAA/.NCEP/. 

 EMC/.CMB/.GLOBAL/.Reyn_SmithOIvl/.monthly/.ssta/ 

 laccessed on 9 February 2002]. 



" CPC (Climate Prediction Center). 2002. Monthly atmo- 

 spheric and SST indices. Website: http://www.cpc.ncep.noaa. 

 gov/data/indices/index.html [accessed on 9 February 2002J. 



substantial increments, 85% from 1991 to 1992, 54% 

 from 1992 to 1993, 102% from 1995 to 1996, and 102% 

 from 1997 to 1998. In particular, the sum of the two El 

 Niiio years in the record (1991-93, 1997-98) represents 

 59.5% of the total catches over the 10-year period. 



Latitudinal variation in YFT catches 



Figure 3 shows the variation of catch and effort (in sets) 

 from 1990 to 1999. Vertical bars include catches from dif- 

 ferent one-degree latitudinal range areas between 18°N 

 and 24°N and meridional ranges between 104°W to 112°W 

 (Fig. IJ. With the exception of the southern 18-20°N area, 



