areas. They include several medium- 

 sized (32-125 kg) bluefin as well as a 

 few larger individuals, in the area 

 bounded by latitudes 37°30'N to 

 40°30'N and longitudes 66°20'W to 

 70°00'W, well north of nearly all of the 

 recorded captures of larvae and small 

 juveniles in the western North Atlantic. 

 Nearly ripe large bluefin tuna have also 

 been encountered in the northwestern 

 Caribbean Sea and northeast of the Ba- 

 hamas, where no larvae or small juve- 

 niles have yet been found. 



The capture of larvae depends not 

 only on their abundance but also on the 

 intensity and seasons of the collecting 

 effort. Additional planktonic surveys 

 in the proper seasons would probably 

 have extended the areas of known oc- 

 currences of larvae and small juveniles 

 considerably. 



b. Specific Occurrences 



The most numerous and wide- 

 spread collections of larval and juve- 

 nile bluefin tuna fi-om the western North 

 Atlantic area were taken in the Gulf of 

 Mexico. During extensive 

 ichthyoplankton surveys of the Gulf by 

 the Centro de Investigaciones Pesqueras 

 of Cuba in April to May 1973, and in 

 May to June 1974, numerous bluefm 

 tuna larvae were taken over extensive 



areas (Juarez, M. 1 974b, Montolio and 

 Juarez, M. 1 977) (Figure 68). The rela- 

 tive abundance of larvae per 1 00 m^ 

 was calculated by the formula: 



NT/V X 1 GO 



where: 



N is the number of larvae per tow, 



T is the depth of the thermocline and 



V is the volume of water filtered in 

 m'. 



In the 1973 cruise, which covered 

 the eastern half of the Gulf, larvae were 

 taken in varying numbers at 13 of the 

 46 stations which were occupied (Juarez 

 1974a, 1974b). Most of the larvae were 

 captured in the north central Gulf at 1 1 

 stations within the area bounded by 

 latitudes 25°N and 30° N and longi- 

 tudes 87°W and 9rw, Others were 

 taken at a station at about 26°N latitude 

 and 84°30'W longitude, and another at 

 about 24°N latitude and 88°W longi- 

 tude. 



The April to May collection data 

 indicated relative abundances of blue- 

 fin larvae of up to 2,000 per 100 ml 



Relative abundance of larvae 

 (number per 100 m^ of sea surface) 

 were 2,000 for one station, 649 at an- 



40" 



LEGEND 



o LARVAL <13mm 

 + JUVENILE 13-120 mm 

 MONTH- N = NUMBER CAPTU) 



30* 



20- 



100' 



Figure 67. Collection locations for larval and juvenile bluefin nina in the western 

 North Atlantic. 



other, 101 to 33 1 at three stations, and 

 1 00 or less at eight stations. No bluefin 

 were captured at the other 33 stations. 

 The estimated number of larval T. 

 thynnus thynnus in the area, on the 

 basis of Juarez's (1974b) data, was 

 3 1,442 X lO^Richards 1976). Bluefm 

 tuna constituted 24.6 percent of all of 

 the larvae of the family Scombridae 

 collected during this cruise (Juarez 

 1974b). 



Bluefin tuna larvae were much 

 more available during the May to June 

 1974, cruise, which sampled nearly all 

 of the deep (over 200 m) waters of the 

 Gulf Larvae of this species were col- 

 lected at 23 of the 61 stations occupied 

 (Montolio and Judrez 1977). All of the 

 successful stations were between lati- 

 tudes 23° and 28°30'N, and longitudes 

 84°30' and 94° 30'W. Nearly all of 

 them were between 40 and 140 nauti- 

 cal miles (74 and 140 km) from the 200 

 m contour. Five stations yielded more 

 than 1,000 bluefin per 100 m^ each. 

 These stations were rather scattered, 

 with one at 24°N, 87°W, another at 

 28°N, 87°W, one at 27°30'N, 90°W, 

 and two near 26°N, 94°30'W. From 

 501 to 1,000 per 100 m' r thynnus 

 thynnus larvae were taken at five sta- 

 tions well spread over the area. Ten 

 stations produced 1 1 -500 per 1 00 ml 

 and only two of the successflil stations 

 yielded 1 00 or less. Results at one posi- 

 tive station were not reported. No blue- 

 fin larvae were collected at the 38 re- 

 maining stations. The larvae of 7". 

 thynnus thynnus constituted 47.7 per- 

 cent of all of the larvae of the family 

 Scombridae which were collected dur- 

 ing this cruise (Montolio and Jaurez 

 1977). 



The May to June 1974 cruise 

 showed that the spawning of bluefin 

 extended over much of the deep water 

 of the Gulf of Mexico north of 23°N 

 latitude in that period. Comparisons 

 with the results of the April to May 

 1973 cruise suggest that bluefin tuna 

 larvae are much more available in the 

 Gulf in May and June than in April and 

 May, and consequently that spawning 

 is more intense in June than in April. 

 This is in agreement with other avail- 

 able indications, but this comparison 

 might have been biased by better spawn- 

 ing success in one year than the other. 



"Numerous" bluefin tuna larvae 

 4.2-10.2 mm SL were collected at 



80 



