the northern Gulf in January and Feb- 

 ruary. 



The available evidence indicates 

 that the distribution of bluefm in this 

 wintenng area is rather sparse and 

 patchy This estunate may be biased, 

 however, since most of the longline 

 fishing effort in the area was prob- 

 ably directed toward yellowfin tuna 

 rather than bluefin. 



The situation off the "bulge" of 

 easternmost Brazil and in the narrow 

 "waist" of the Atlantic between there 

 and western Africa was more com- 

 plex. Concentrations of bluefin oc- 

 curred off the "bulge" in each quar- 

 ter of the year (Figure 32). Examina- 

 tion of the monthly charts suggests 

 that two separate concentrations de- 

 veloped there, and then dispersed, 

 during each year. 



Bluefin were thinly distributed 

 across the "waist" in July and Au- 

 gust. In September a concentrafion 

 (bounded approximately by the Equa- 

 tor and latitude 15°N and by longi- 

 tudes 25°W and 40°W) formed in 

 this area The maximum catch rates 

 exceeded one fish per 1,000 hooks. 

 In October and November this con- 

 centration moved slowly southward, 

 until its southern edge was at about 

 15°S latitude In December, bluefin 

 were still present in the area, but the 

 catch rates were all below one fish 

 per 1,000 hooks This concentration 

 probably did not consist of recent 

 migrants irom the North Atlantic The 

 giant bluefin do not usually leave 

 their feeding grounds there until late 

 September or October (see Sections 

 1VC2 and IVC5) and this concentra- 

 tion had already developed in tropi- 

 cal waters in September. 



The distribution of bluefin in the 

 "waist" was generally thin in Janu- 

 ary, with more fish off the "bulge" 

 than elsewhere In February, how- 

 ever, the catch rates in the latter area 

 increased, and a new concentration 

 had definitely formed by March. This 

 extended approximately from 20°S 

 to 5°N latitude, and fi-om 25°W lon- 

 gitude to the South Amencan coast 

 Catch rates in this area were espe- 

 cially high in the years 1962 through 

 1965, sometimes exceeding 20 fish 

 per 1,000 hooks Since then, fishing 

 in the area has been infi-equent, and 

 catch rates have generally been low 



The available information indi- 

 cates that the bluefin taken in this 

 area were giants Zharov (1965), re- 

 porting on exploratory and commer- 

 cial catches taken in the penod fi"om 

 February through June 1963, off the 

 South American coast from 11°S to 

 1 TN lafitude, stated that the bluefin 

 ranged from 205 to 254 cm in length, 

 with an average of 224 cm, and from 

 151 to 283 kg in weight, with an 

 average of 1 83 kg. Thus all of them 

 were in our "large" category. Shingu 

 et al. (1975) also reported that the 

 bluefin taken by longline in the equa- 

 torial Atlantic off northeastern Bra- 

 zil were of large size. 



The April catch rate disfributions 

 (Le Gall 1 974) show that the area of 

 high apparent abundance had ex- 

 panded northeastward into the Gulf 

 of Guinea, and northwestward almost 

 to southeastern Florida The latter 

 extension of high catch rates, in our 

 opinion, represents a major migra- 

 tion of giant bluefin from the winter- 

 ing area described above to the 

 spawning grounds in the "American 

 Mediterranean" and in Atlantic wa- 

 ters east of the Bahamas and Florida 

 (Section VD3). This route would fol- 

 low the major branch of the North 

 Equatorial Current off the northwest- 

 ern coast of South America (Sverdrup 

 et al. 1942) for much of the 3,500 

 nautical mile (6,575 km) distance 

 As stated previously, large bluefin 

 tend to fravel with favorable currents 

 when they are migrating for long dis- 

 tances. The change in the areas of 

 high catch rates from March to April 

 indicates that this migration might 

 have been completed in about a 

 month This would have required an 

 average speed of about 5 knots (9 km 

 per hour), with considerable help 

 from favorable currents This rate of 

 migration is not inconsistent with 

 those cited previously in this section 

 for migrations between other areas, 

 or for estimates of observed migra- 

 tory speeds. 



This hypothetical migration has 

 not been venfied by lag returns, since 

 no bluefin have been tagged m the 

 South Atlantic As noted previously, 

 however, two fish tagged off the Ba- 

 hamas have been recaptured off east- 

 em Brazil, or .south of there. The 

 sizes given by Zharov (1965) for fish 



caught off eastern Brazil and along 

 this proposed migration route, more- 

 over, are in close agreement with the 

 correspondmg figures for fish taken 

 in the Straits of Florida m May and 

 June, prior to the recent increases in 

 the sizes of giants taken there and 

 elsewhere (Rivas 1955, 1976, Mather 

 1963a, 1974, Mather etal. 1974a). 



Other contingents probably fol- 

 low more northerly branches of the 

 North Equatorial Current from mid- 

 Atlantic wintermg areas, where their 

 relative abundance is lower than off 

 the "bulge", and join this migration 

 off northeastern South America or 

 the Antilles Still others may migrate 

 directly westward, or even southwest- 

 ward, from more northerly oceanic 

 winter habitats to the spawning 

 grounds 



While many giant bluefin evi- 

 dently make lengthy migrations be- 

 tween their wintering and spawning 

 areas, others, which have vvmtered 

 farther north and west, east of the 

 Bahamas, or in the American Medi- 

 terranean may reach their spawnmg 

 grounds with relatively little move- 

 ment In the extensive areas where 

 the proposed wintering and spawn- 

 ing areas overlap, the fish might re- 

 produce wherever they happen to be 

 when the spawning penod occurs. 



The disfributions of the higher 

 spring longline catch rates (LeGall 

 1 974) suggest that most of the giant 

 bluefin which migrated northwest- 

 ward along the South American coast 

 subsequently followed the Antilles 

 Current in the Atlantic east of the 

 Antilles and the Bahamas, instead of 

 the North Equatorial and Flonda Cur- 

 rents which flow through the Carib- 

 bean, the Yucatan Channel, the Gulf 

 of Mexico and the Sfraits of Flonda 

 (Sverdnip etal. 1942). 



As noted previously, these catch 

 data may have been biased by spotty 

 fishing effort in the Caribbean and 

 the Gulf, and its possible direction 

 toward yellowfin, rather than blue- 

 fin, tuna Even allowing for these 

 factors, the spring catches of bluefin 

 in the eastern and southern Canb- 

 bean have been very scarce. In re- 

 cent years, on the other hand, effort 

 directed toward bluefin in the north- 

 ern Gulf of Mexico during the spawn- 

 ing season has produced consider- 



123 



