FISHERY BULLETIN: VOL. 73, NO. 2 



Table 8.-Number of skipjack gonads in each maturity stage by 

 size of fish, Cruises Jordan 57-Cromwell 51, November- 

 December 1970. 



Totals: males (M) 24; females (F) 28; Indeterminate (<40 cm) 15. 



Table 9.-Number of skipjack gonads in each maturity stage by 

 size of fish, Cruise Jordan 60, March-April 1971. 



<40 

 40-49.9 

 50-59.9 

 60-69.9 



>70 



2 



1 1 



2 



1 



10 



5 



1 



13 



8 



Totals: males (M) 24; females (F) 34. 



63% and 67%, respectively, in March-April 1971 

 (Tables 8, 9). Most others were at the immature 

 resting stage. The spent-recovering fish appeared 

 to be at a more advanced stage of recovery in 

 March- April than in November-December 1970. 



Data on other skipjack ovaries taken from or 

 near the study area in 1970-71 are available from 

 samples of purse seine-caught fish examined by 

 the Inter-American Tropical Tuna Commission (C. 

 L. Petersen, pers. commun.). Gonad indices were 

 calculated by them according to Orange (1961), 

 and data are given in Table 10. 



The principal interest lies in the samples (mean 

 lengths >57 cm) from long. 110°W westwards. It 

 is assumed that gonad indices < 15.1 indicate 

 immature (virgin or resting) or spent-recovering 

 ovaries, 15.1 to 45 indicate maturing ovaries, and 



> 45 indicate mature or ripe ovaries. The oc- 

 currence of 35% of skipjack ovaries with indices 



> 45 in the middle of the study area in September 

 1970 may correspond to the 36% of ovaries in spent 



condition in fish > 50 cm in the same area in 

 November-December 1970 (Table 8). The sample 

 from lat. 5°N, long. 110°W in April 1971 (Table 10) 

 showed similar ovarian states to those in skipjack 

 > 50 cm caught in March-April 1971 (Table 9): 

 about 75% immature or spent-recovering, and 25% 

 maturing, in each case. 



Sex and Maturity of Yellowfin 



In November-December 1970, 24 specimens of 

 yellowfin under 50 cm were classified as immature, 

 sex indeterminate; of 5 yellowfin from 50 to 60 cm, 

 3 were immature female, 1 was immature male, 

 and 1 was indeterminate. 



OBSERVATIONS ON THE 



ENVIRONMENT IN RELATION 



TO SKIPJACK 



Temperature 



The data from Part I operations on the 1970 and 

 1971 cruises were used to construct temperature 



Figure lO.-Temperature (°C) section from lat. 15°N to 5°S 

 along long. 119°W, cruise Cromwell 51, 1-7 November 1970. 



23 August 1970 

 8 September 1970 

 April 1971 

 30 April 1971 

 May 1971 



135 



120 



110 



90 



90 



48.9 



2.5 



76.0 



57.1 

 32.0 



46.8 

 62.5 

 24.0 

 42.9 

 60.0 



4.3 

 35.0 

 

 

 8.0 



50 

 40 

 50 

 49 

 59 



53.5-63.8 

 55.0-62.3 

 54.3-67.6 

 53.3-68.7 

 57.8-70.0 



59.9 

 57.8 

 60.5 

 62.3 

 64.5 



392 



