3. Western North Atlantic 



The western North Atlantic is the 

 only part of that ocean from which 

 extensive collections of early stages of 

 T. thyiinus thynnus have been obtained. 

 The most important occurrence docu- 

 mented up to now has been in the Gulf 

 of Mexico. Bluefm larvae and small 

 juveniles have been collected over 

 much of the deep (more than 300 m) 

 part of the Gulf, especially in the area 

 north of latitude 23 °N (Judrez 1972 

 1 974b; Richards 1976, 1977;Montolio 

 and Ju^ez 1977, T.C. Potthoff, per- 

 sonal communication). Important col- 

 lections have also been made in the 

 Straits of Florida, particularly at the 

 Dry Tortugus and off Miami (Potthoff 

 and Richards 1 970, Richards 1 976, T.C. 

 Potthoff, personal communications). 

 Scattered individuals have been col- 

 lected off the east coast of the United 

 States up to latitude 38°45'N. These 

 collections show that the Gulf of 

 Mexico is the most important bluefrn 

 tuna spawning ground yet discovered 

 in the Atlantic, and that spawning also 

 occurs in the Straits of Florida and prob- 

 ably for an unknown distance farther 

 north. 



The condition of gonads of cap- 

 tured fish suggests that spawning may 

 also take place in the northwestern Car- 

 ibbean, the Windward Passage, the Old 

 Bahama and Santaren Channels, and a 

 large area east and north of the Baha- 

 mas. Virtually all of the mature bluefin 

 taken in these southerly parts of the 

 western North Atlantic and adjacent 

 waters for which we have size data 

 were large (over 185 cm long) indi- 

 viduals, weighing over 125 kg. Exami- 

 nations of gonads suggest that at least 

 some smaller bluefin spawn near the 



northern edge of the Gulf Stream, or 

 the Gulf Stream front, north of latitude 

 37°N and east of longitude 70° W. 



4. Overall Situation 



On the most positive evidence 

 available, the occurrence of larvae and 

 very small juveniles, one can only con- 

 clude that the most important spawn- 

 ing areas of T. thymus thynnus are in 

 the south central Mediterranean Sea 

 and the Gulf of Mexico. This in itself is 

 an interesting parallel, as the Gulf of 

 Mexico and the Caribbean Sea are of- 

 ten referred to as the "American Medi- 

 terranean." 



The major spawning occurs ear- 

 lier in the western Atlantic (probably 

 about May 15-June 15) than in the 

 Mediterranean (about June 1 5-July 15). 

 The smaller bluefin spawn later 

 than the larger ones in the Mediterra- 

 nean, and probably do in the western 

 Atlantic also. Studies of spawning in 

 both areas have centered on the larger 

 fish. Some information is available on 

 the spawning of the smaller individuals 

 in the Mediterranean, where they mix 

 to a considerable extent with the larger 

 ones during the spawning season. The 

 two groups evidently reproduce sepa- 

 rately in the western Atlantic, and much 

 less is known about the spawning of 

 the smaller fish (all of the "medium" 

 size group, and the mature members of 

 the "small" group) there. 



The only occurrence of early stages 

 of bluefin in the eastern North Atlantic, 

 or the South Atlantic of which we have 

 knowledge is the collection of a very 

 few larvae near the Equator and longi- 

 tude 7°W. Much more information will 

 be needed to determine the significance 

 of this unexpected finding. 



Other collections of larvae, al- 

 though less important than those from 

 the Gulf of Mexico and the central 

 Mediterranean, indicate that bluefin 

 spawn around the Balearic Islands, in 

 the Black Sea, in the Straits of Florida 

 and, probably, north of the Bahamas. 



Studies of the maturity of gonads 

 suggest spawning over more extensive 

 areas. Ihese would include major 

 spawning along the coasts of Tunisia 

 and Tripolitania, and in the Ibero-Mo- 

 roccan Bay (by the fish which do not 

 enter the Mediterranean to spawn). 

 Spawning in the Bay of Biscay is also 

 indicated but this is probably less im- 

 portant. Gonad studies in the western 

 Atlantic suggest, extensive additional 

 spawning areas off Cuba, the Baha- 

 mas, and the southeastern United States 

 along the Gulf Stream front north and 

 east of Cape Hatteras. 



Judrez (1974b) and Montolio and 

 Juarez ( 1 977) provided quantitative es- 

 timates of the numbers of bluefin lar- 

 vae in extensive areas of the Gulf of 

 Mexico. Richards ( 1 976) estimated the 

 number offish in the spawning stock 

 from the estimated number of larvae 

 (Juarez 1974b). His figure was in rea- 

 sonable agreement with those calcu- 

 lated by other methods. 



No quantitative estimates of the 

 abundance of bluefin tuna larvae in the 

 Mediterranean have been published. C. 

 Piccinetti (personal communication), 

 however, informed the senior author 

 that the relative abundance of larvae in 

 the Gulf of Mexico, as indicated by 

 Montolio and Judrez ( 1 977), was much 

 less than that which he and his col- 

 leagues had found in parts of the Medi- 

 terranean. 



95 



