FISHERY BULLETIN: VOL. 80, NO. 1 





I mm 





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Figure 4.— Ovarian tissue from an age 6 bluefin tuna (153 cm, 59.5 kg) collected off the Middle Atlantic 

 Bight during June 1976. Resting stage 2 oocytes are present (upper arrow), as are stage 3 oocytes 

 undergoing the process of degeneration (lower arrow). 



developed oocytes in the majority of fish that I 

 examined were in stage 3 of development, and 

 the average were in stage 2 based on the mean 

 size of the oocytes measured (Fig. 5). 



I believe, therefore, that the Middle Atlantic 

 Bight is not a significant spawning area during 

 the summer and probably not at any other time 

 of the year, but samples are not available for 

 other seasons. Also, recently there has been 

 speculation by Rivas (1978) that some of these 

 medium bluefin tuna may migrate during May 

 and June across the Atlantic to the Mediter- 

 ranean Sea to spawn. According to Sella (1929) 

 eastern Atlantic bluefin tuna begin to reproduce 

 in their third year, when they attain a weight of 

 about 15 kg. Rodrlguez-Roda (1967) found that 

 50% of eastern Atlantic bluefin tuna females are 

 mature at 97.5 cm or 3 yr of age. However, the 

 smallest bluefin tuna that he estimated fecun- 

 dity for was 130.5 cm and 54 kg, which corre- 

 sponds to an age 5 fish according to Coan (1976). 

 Frade and Manacas (1933) found very little 



development in age 3 females from the eastern 

 Atlantic. Cort et al. (1976) found developing 

 oocytes in eastern Atlantic bluefin tuna measur- 

 ing 148 and 152 cm from the Gulf of Gascony. 

 These fish would be age 6 according to Coan 

 (1976). 



The only published record I have found of age 

 of maturity of western Atlantic bluefin tuna is 

 that of Westman and Neville (1942). Observing 

 the gross morphology of ovaries, they indicated 

 that western Atlantic bluefin tuna 5 yr of age 

 appeared to be mature, although the gonads gave 

 no indication of the presence of eggs. I have also 

 examined the unpublished cruise report of the 

 MV Delaware, June 1957. Using the conversion 

 table of Coan (1976), all age 3 female bluefin 

 tuna were judged immature, and most age 4 (2 

 out of 3) were judged immature. No description 

 of the ovaries on an age 5 fish was given, and 67% 

 of age 6 females (N = 6) had well-developed eggs. 



My analysis of western Atlantic bluefin tuna 

 ovaries indicates that age 6 would probably be 



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