Less information is available on 

 the age of first spawning of western 

 Atlantic bluefin, but these fish have 

 apparently been less precocious than 

 their eastern Atlantic and Mediterra- 

 nean counterparts. 



Westman and Neville (1942) ex- 

 amined many small and medium sized 

 bluefin tuna landed by the coastal sport 

 fishery at Freeport, Long Island, New 

 York. They reported that nearly all of 

 the "school tuna" (fish averaging less 

 than 30 kg) were immature. They found 

 some evidence of approaching matu- 

 rity in a few tuna of the 3 -year-old age 

 group, and signs of maturity in a larger 

 percentage of the 4-year-olds. They con- 

 sidered all of the fish of both sexes 

 which were 5 years old (about 1 30 cm 

 long and weighing about 40 kg) or 

 older to be adults, but found no indica- 

 tions of eggs or sperm in their gonads. 



The present authors have con- 

 ducted macroscopic examinations of 

 the gonads of numerous small bluefin 

 tuna caught in traps or by sport fishing 

 in southern New England coastal wa- 

 ters and by purse seines in coastal wa- 

 ters between southern New Jersey and 

 New England in the summers of 1 950- 

 1975. We concur with Westman and 

 Neville's conclusions. We found signs 

 of maturity in less than 1% of the 3- 

 year old fish but in a considerably larger 

 percentage of the tuna of age group 4. 

 Nearly all age 3 fish, like all the 0, 1 , 

 and 2 year-old individuals examined, 

 had very small gonads which were al- 

 most uniformly slender throughout their 

 length, like very flat shoestrings. The 

 gonads of the older fish which were 

 considered to show signs of maturity 

 were distinctly enlarged for at least part 

 of their length. The testes of a few age 

 4 males taken in Cape Cod Bay, Mas- 

 sachusetts, in early July 1953, contained 

 milt. Those of a 4-year-old specimen, 

 110 cm long and weighing 25 kg, 

 weighed 27.5 g and contained milt. A 

 photomicrograph (970x) taken by R. F. 

 Vaccaro, an Associate Scientist of 

 Woods Hole Oceanographic Institution, 

 showed that this milt contained fully 

 developed sperm. The gonads of most 

 of the 5-year-old tuna (about 133 cm 

 long and weighing about 45 kg) were 

 generally better developed, and most 

 of these fish had probably spawned. 



We believe that the mature mem- 

 bers of the "small" bluefin group (less 

 than 120 cm long) spawn in ofTshore 

 waters north of the Gulf Stream, along 

 with fish of the "medium" size group, 

 in May and June. As noted in Section 

 VD3, a few small bluefin and several 

 medium sized ones taken by longline 

 in this area and season were examined. 

 The results of macroscopic examina- 

 tions of their gonads were as follows: 

 Age III. Two fish were examined. Both 



were classified as immature. 

 Age 4. Three males and three females 

 were examined. One fish of each sex 

 showed definite signs of maturity. 

 Age 5. One male was examined. Some 



milt was squeezed from its testes. 

 Age 6. Twelve fish (six of each sex) 

 143.5-157 cm long and probably of 

 this age were examined. Two of the 

 females were classified as spent. The 

 other ten fish appeared to be ap- 

 proaching spawning condition. 

 We conclude tentatively from all 

 of these data that the first spawning of 

 bluefin tuna in the eastern Atlantic oc- 

 curs at age 3, in exceptional cases, and 

 more frequently at age 4. By age 6 all, 

 or nearly all, of the fish are spawners. 

 Probably the first spawning of western 

 Atlantic bluefin tuna occurs most fre- 

 quently at age 5, but more research is 

 required to establish this. 



2. Fecundity 



Rodriguez-Roda (1967a) found 

 that the estimated fecundity of bluefin 

 tuna caught near Cadiz, Spain, in May 

 and June generally increased with size 

 offish, from 5.2 x 10" for an individual 

 130.5 cm long and weighing 54 kg to 

 32.2 x 10'' for one 230 cm long and 

 weighing 235 kg The minima and 

 maxima, however, were 5.0 x 1 0'' for a 

 fish 160 cm long and weighing 96 kg, 

 and 45.9 X 1 O*" for one 214cm long and 

 weighing 191 kg. He calculated the 

 following relationships between F, tlie 

 fecundity or number of maturing eggs, 

 and (1) L, the length of the fish in cm; 

 (2) and (3) P,, the weight of the fish in 

 kg; and (4) P^, the weight of the ovaries 

 in kg: 



(1) F = 2.29245 L^ 



(2) F = 53,451 P^ii""*' 



(3) F = -1,220,71 7+ 138,068 P, 



(4) F = 553 P, ' "'"" 



In the size range studied, the esti- 

 mated fecundity was thus roughly pro- 

 portional to the weight of tlie fish, or 

 the third power of its lengtli. 



Baglin (1976), studying six blue- 

 fin tuna taken near Bimini and Cat Cay 

 in the northwestern Bahamas in May 

 and June and ranging from 222.5 cm in 

 length and 1 88.4 kg in weight to 260.6 

 cm in length and 271.5 kg in weight, 

 found that their estimated fecundity in- 

 creased from 16.7 x 10" for the smallest 

 to 3 1 .4 x lO" for the largest. The maxi- 

 mum, however, was 33.0 x lO' for an 

 individual 240.8 cm long and weigh- 

 ing 247.4 kg. Where F is the estimated 

 fecundity, L is the length of the fish in 

 cm, W is its live weight in kg, and W^ is 

 the dry weight in g of all of the eggs 

 from both of its ovaries, Baglin calcu- 

 lated that: 



F = 65.421 4 L"'"" 



F = 6,245,010 + 95,132.3 W 



F- 3,051,104+ 18,916.4 W,. 

 He concluded that fecundity increased 

 with size of fish in the length range 

 from 222.5 cm and to 260.6 cm, and 

 that, therefore, larger fish contribute 

 more to the reproductive potential. 



No significant difference in the 

 slopes or adjusted means was found by 

 Baglin in a covariance analysis between 

 the fecundity-length and the fecundity- 

 weight relationships found in his study 

 of western Atlantic bluefin tuna and 

 those found by Rodriguez-Roda 

 (1967a) for eastern Atlantic individu- 

 als. Baglin noted, however, that the 

 samples were small, and that more ex- 

 tensive studies might reveal significant 

 differences. 



The studies of Rodriguez-Roda 

 (1967a) and Baglin (1976) indicate 

 clearly that the fecundity of Atlantic 

 bluefin tuna increases with size offish, 

 in both the eastern and western parts of 

 the Ocean. Baglin's study shows that 

 this relationship extends to the very 

 large size of 260 cm. Pending actual 

 determinations of the fecundity of larger 

 fish, there is no reason to suppose that 

 the fecundity does not also increase 

 with size of fish for the relatively few 

 larger individuals which are captured. 

 Baglin and Rivas (1977) estimated the 

 fecundity of 1 7-year-old Atlantic blue- 

 fin as 44.6 x 10" eggs. 



93 



