Table 22. Indices* of maturity for 140" bluefin tuna taken in the Los Cenizosos 

 trap (near Larache. Morocco) in May and June 1955 by sex and 10-day period 

 (Lozano Cabo 1958). 



■ The index of maturity is the ratio of the total weight of the fish to the weight of its gonads. 



" Seventy-six were examined individually in the first three periods. The index for the la.sl 



period was obtained by dividing the total weight of 64 fish by the total weight of their 



tions were too few to be conclusive, 

 but hoped that future research might 

 determine the possible existence of a 

 bluefin spawning ground in the Bay of 

 Biscay. 



Aloncle (1964) found that many 

 30-60 kg bluefin wintered between the 

 Canary Islands and Morocco and hy- 

 pothesized that one group of them 

 spawned between Lanzarote Island (Ca- 

 naries), Conception Bank, and the Mo- 

 roccan coast. Distributional data sup- 

 port this hypothesis, but studies of go- 

 nad condition and collections of eggs 

 and early stages are required to verify 

 it. 



Ferreira (1932) reported that ripe 

 bluefin were sometimes landed in the 

 Azores in spring, but his statistics indi- 

 cated that the species was not abundant 

 there. 



The only reports of larval bluefin 

 taken in the eastern Atlantic are from 

 equatorial waters off Africa. Fourteen 

 small larvae (mostly 2.5-4.5 mm long) 

 were taken in the area bounded by lati- 

 tudes 6°N and 8°S and longitudes 0° 

 and 1 5°30' W. One of these was col- 

 lected in February, eight in March and 

 five in August (Richards 1 969, Richards 

 and Simmons 1971, unpublished 

 NMFS data reports for Geronimo 

 cruises 3, 4 and 5). The surveys in 

 which these collections were made were 

 carried out in the periods February- 

 April and August-October, missing 

 most of the period in which the eastern 



Atlantic bluefin are believed to spawn. 

 The oceanic distribution of bluefin tuna 

 (Wise and Davis 1973) in the first quar- 

 ter of the year shows concentrations of 

 bluefin near where these larvae were 

 found, but the distribution in the third 

 quarter does not. It would be desirable 

 to conduct a survey in this area in the 

 second quarter, and also to examine the 

 gonads of bluefin caught there in the 

 months of February through August. 



Much remains to be learned about 

 the spawning of bluefin in the eastern 

 Atlantic, and about the possible role of 

 the Mediterranean, both as a spawning 

 ground and a nursery area for bluefin 

 tuna from the eastern Atlantic. The de- 

 gree of mixing of adults and new-bom 



Atlantic and Mediterranean tuna, if they 

 are indeed separate, is another impor- 

 tant matter about which there is no 

 quantitative information. In view of the 

 possible passive transport of spawning 

 products from the Ibero-Moroccan Bay 

 into the Mediterranean, the technique 

 of collecting pelagic eggs, hatching 

 them, and rearing the larvae to identifi- 

 able size appears to be the most prom- 

 ising approach to solving the important 

 problem of whether bluefm tuna actu- 

 ally spawn there. The failure to find 

 identifiable eggs or early stages of blue- 

 fin in the Alboran Sea (westernmost 

 Mediterranean) as well as in the Ibero- 

 Moroccan Bay during the 1923 and 

 1972 surveys, however, does not sup- 

 port the theory of passive drif^ of spawn 

 from the latter area to the former. 



3. Western North Atlantic 



a. General Information 



Important information on the 

 spawning of Thiomus thynmts thynnus 

 in the western North Atlantic has been 

 obtained through collections of larvae 

 and juveniles. Ripe or nearly ripe fish 

 have been captured over extensive ad- 

 ditional areas. 



The great majorit\ of the captures 

 of larvae and juveniles have occurred 

 in the Gulf of Mexico and the Straits of 

 Florida. Scattered occurrences farther 

 north include one larva east of northern 

 Florida and seven juveniles (17. 5-33. 2 

 mm SL) off the Carolinas, Maryland 

 and New Jersey (Figure 67). 



Occurrences of ripe or nearly ripe 

 fish have spread over some additional 



Table 23. Variations in the mean gonado-somatic indices'" of bluefin tuna*" taken 

 in the trap at Moulay-bou-Selham (near Kenitra. Morocco) in May and June, 

 1955 (Fumestin and Dardignac 1962). 



79 



