■^^■^-yy 



Figure 65. Bluefin spawning areas in the Eastern Atlantic and the Mediterranean 

 and Black Seas. 



for stages of maturity, based on the 

 color of the ovaries: 



I. Immature: Gonads of rosy color. 



II. Prematuration: Male gonads of a 

 violaceous color, and female of a 

 rose color. 



III. Maturation: Male gonads of a 

 rose or a rosaceous white color, 

 and female yellow rose or yellow- 

 ish. 



IV. Prespawning: Male gonads of a 

 milky violaceous color. 



V. Spawning. 



VI. Postspawning: The male and fe- 

 male gonads are of a violet color. 



Very swollen ovaries with most of 

 the eggs transparent were considered 

 to be in stage V, Only one such female 

 was observed during the "return" pe- 



riod and it was concluded that its ovi- 

 duct was probably obstructed. 



During the "arrival" run in May 

 and June the bluefin tuna appeared with 

 turgid gonads in a state of prematuration 

 or maturation and in the "return", in 

 July and August, the gonads were al- 

 ready flaccid and with obvious signs of 

 having emitted the eggs. Between these 

 two phases, at the end of June and early 

 in July, when spawning should actu- 

 ally occur, the bluefin disappeared from 

 the coast and its captures were very 

 limited. 



To define the spawning period, 

 the monthly percentages of the sexual 

 stages for 779 males and females ex- 

 amined at the Barbate trap from 1956 

 to 1959 are shown in Table 20. 



The majority of the fish were in a 

 prespawning state (stage III) in May 

 and June and in the post-spaw ning stage 

 (stage VI) in July and August. The 

 small percentage of tuna ol'both sexes 



which were in stages I and II were not 

 large individuals. Those in stage I in 

 June were ^5 and 80 cm long, res- 

 pectively. Those of both sexes in stage 

 II were 1 15 to 140 cm long, excepting 

 two females 170 and 175 cm long. In 

 July and August a few bluefin were in 

 the prespawning state. One male 135 

 cm long was in stage II in July. Males 

 and females from 125 to 220 cm long 

 in July, and 125 to 135 cm long in 

 August, were in stage III. The onl\ 

 specimen in stage IV was a male 170 

 cm long taken in June. 



Rodriguez-Roda ( 1 964a) also used 

 an index of maturity, the "gonosomatic 

 relation", equal to 100 times the ratio 

 of the weight of the gonads to the total 

 weight of the fish, to evaluate relative 

 fecundity. He also provided plots and 

 formulae showing the relationships be- 

 tween the weight of the gonads and the 

 fork length of the fish for bluefin tuna 

 during the "arrival" and "return" peri- 

 ods. 



He tabulated the gonosomatic re- 

 lation for males and females, by 5-cm 

 length groups and 10-day periods, for 

 260 "arrival" and "return" fish exam- 

 ined in 1956, and also for 198 exam- 

 ined in 1958 (Tables 21a and 21b). 



This index generally increased with 

 size of fish. Its mean value also in- 

 creased during the "arrival" period in 

 June, for both sexes, then descended 

 abruptly in the months of July and Au- 

 gust, in the "return" period. All this 

 confirmed spawning in early July. In 

 general, the index was higher for fe- 

 males than for males. 



The condition of the gonads of 

 bluefin tuna taken off the Atlantic coast 

 of Morocco was examined by Lozano 

 Cabo (1957, 1958) and Furnestin and 

 Dardignac ( 1962). Lozano Cabo( 1958) 

 tabulated, by sex and 10-day period, 

 the minimum, mean, and maximum 

 indices of maturit}' of samples of blue- 

 fin tuna taken in 1955 by the trap at Los 

 Cenizosos (near Larache) in 1^)55 

 (Table 22) 



The mean index for females de- 

 creased from 80.8 in the last ten days of 

 May to values between 46.2 and 40.0 

 in the three ten day periods in June. In 

 the second ten days of May a few fe- 

 males with very low maturity (indices 

 averaging 105. 3) were examined. When 

 these fish were being taken, the catch 

 was very small. The fisher) did not 



74 



