Table 17. Indices of maturity and condition of gonads (Frade 1937a). 



Table 18. Stages of maturity for 1 7 1 bluefin tuna examined at Vila Real de Santo 

 Antonio. Portugal. May 31-August 18, 1933 (Frade 1937a). 



60 



50 



>40 



^30 



10 

 



FEMALE 



MALE 



A B C D E F G 



F G 



Figure 66. Plot showing the changes in sexual maturity of Atlantic bluefin tuna 

 by month. The data are the same as in Table 18. 



become productive until the index 

 reached 63.6 (LozanoCabo 1957). The 

 maturity of the females decreased 

 slightly (index rising fi-om 40.0 to 43.9) 

 from the second to the third ten days of 

 June. This was caused by the capture of 

 some spent, post-spawning, or "return" 

 fish in this "arrival" trap. The only in- 

 dices for males, taken in the last ten 

 days of May, ranged from 42.7 to 1 3 1 .2. 

 with a mean of 76.8. These figures do 

 not differ greatly from those for fe- 

 males taken in the same period. 



Fumestin and Dardignac (19^2) 

 tabulated the mean "gonado-somatic 

 indices" (evidently the "gonosomatic 

 relation" ofRodriguez-Roda 1964a) for 

 males and females taken in the trap at 

 Moulay-bou-Selham (near Kenitra) in 

 the first and second halves of May and 

 the first half of June (Table 23). 



The indices for males increased 

 rather regularlv from 1.10 in the first 

 half of May to 2.04 in the first half of 

 June. Those of the females followed a 

 similar trend, from 1.52 to 1.99 over 

 the same period. TTiese values showed 

 a more consistent increase in maturity 

 through the season than those of Lozano 

 Cabo ( 1 958). Fumestin and Dardignac 

 ( 1 962) also plotted the gonado-somatic 

 indices for each sex against the length 

 of fish. Those for females increased 

 with length, but those for males only 

 increased up to a length of 210 cm and 

 decreased slightly in longer individu- 

 als. The authors attributed this to the 

 fact that the largest fish were caught at 

 the beginning of the season, when their 

 mauirit)' would normally have been less 

 advanced. The maturity of the fish taken 

 in the first half of June at Moulay-bou- 

 Selham is generally comparable to that 

 found by Rodriguez-Roda ( 1 964a) for 

 fish taken at Barbate, Spain, in the first 

 twenty days of June. Lozano Cabo 

 ( 1 958), however, reported that the blue- 

 fin tuna which he examined at Los 

 Cenizosos were less mature than those 

 which he had examined at Barbate. 



I'liere is sn^ong circumstantial evi- 

 dence that bluefin tuna spawn in the 

 Ibero-Moroccan Bay, but conclusive 

 proof of this is lacking. Great numbers 

 of maturing individuals occur there in 

 May and June, and recently spent fish 

 are abundant in July and August. The 

 stages of maturity of these fish have 

 been verified by many investigations. 

 On the other hand, much research and 



75 



