"Delaware" in this area and season, 

 indicate that at least some of the me- 

 dium-sized and the larger "small" blue- 

 fin have spawned in May and June in 

 the waters north of the Gulf Stream off 

 the northeastern United States. We have 

 noted (Section VC 1 ) that ripe or nearly 

 ripe bluefin may have travelled consid- 

 erable distances in short periods before 

 their capture. In this case, however, 

 Wathne (1959), Wilson and Bartlett 

 (1967), and all the additional data we 

 have been able to collect on bluefin 

 tuna catches in the western North At- 

 lantic, indicate that medium-sized blue- 

 fin have occurred north of the Gulf 

 Stream during the winter and spring 

 but have been only rarely captured south 

 of it and west of 60^W longitude. It 

 therefore seems unlikely that these fish 

 had migrated from southerly areas im- 

 mediately before their capture. 



Baglin (1976) presented a histo- 

 gram showing the "gonadal-somatic in- 

 dex" (the "gonosomatic relation" of 

 Rodriguez-Roda 1 964a) by months for 

 67 bluefin tuna weighing over 100 kg 

 (Figure 69). The specimens were from 

 various areas, but nearly all of those 

 captured in May and June, when the 

 index was at its maximum, were from 

 the vicinity of Bimini and Cat Cay in 

 the Bahamas. The mean gonadal-so- 

 matic indices were about 1.5 in May 

 and 1.0 in June, as against values of 

 from 0.25 to 0.5 in other months. 



The sex ratio for 237 large bluefin 

 tuna which had been captured near the 

 Bahamas in the years 1950-1966 and 

 examined by Woods Hole Oceano- 

 graphic Institution and National Ma- 

 rine Fisheries Service personnel (un- 

 published data) and Rivas (1954) was 

 72% females and 28% males. 



Baglin ( 1 976) also showed the fre- 

 quency distributions of ovum diam- 

 eters for bluefin taken at various dates 

 and in various conditions. He found no 

 developing eggs in bluefin tuna less 

 than 10 years old. He set up a maturity 

 scale based on the gonadal-somatic in- 

 dex, the diameter and morphology of 

 the ova, and the appearance and physi- 

 cal properties of the gonads. He con- 

 cluded that the bluefin spawned in May 

 and June, and probably in April also. 

 He observed that spawning must start 

 south of Bimini and, on the basis of the 

 data from "Delaware" cruise 57-5, 

 might extend as far north as off New 



England, and might involve smaller 

 fish. 



Characteristics of the gonads of 

 giant bluefin tuna collected during ex- 

 ploratory fishing cruises of United 

 States and Russian research vessels in- 

 dicate that these fish may spawn in the 

 northwestern Caribbean, the Windward 

 Passage, the old Bahama and Santaren 

 Channels, and a large area east and 

 north of the Bahamas (Figure 70). Their 

 presence in numbers in the latter area 

 during the spawning season is con- 

 firmed by catches of the Japanese 

 longline fishery (Fisheries Agency of 

 Japan 1971, Wise and Davis 1973). 

 The collection data and sizes of the 

 fish, and their gonad weights and ma- 

 turity indices are shown in Table 25. 



Zharov ( 1 965) observed that large 

 bluefin taken by longline in late May 

 and early June 1963 north of the Baha- 

 mas and east of central Florida (near 

 29°00'N, 79°00'W, and 30°00'N, 

 77°30'W) were "typically spawning, 

 since their sexual products were in 

 stages IV to VI-II" (these stages were 

 not defined). The fish were from 1 98 to 

 238 cm (average 219.4 cm) long, and 

 weighed from 140 to 220 kg (average 

 177.5 kg). 



The information summarized 

 above defines some positive locations 



and periods of spawning of the bluefin 

 tuna, and more extensive tentative ones. 

 The best documented spawning 

 area is in the Gulf of Mexico (Figure 

 68). Bluefin larvae have been collected 

 over much of the deep (more than 200 

 m) area of the Gulf north of 25°N, and 

 also off the northern edge of the 

 Campeche Bank, near 23°30'N and 

 94°30'W, and at 23" 30'N, 85°W. The 

 most thorough and extensive surveys 

 of the area were carried out in April- 

 May 1973, and May-June 1974 (Juarez 

 1974b, Montolio and Juarez 1977). A 

 few specimens have been collected in 

 early July, and one, reportedly, in Au- 

 gust. The last specimen, a 17.1 mm SL 

 juvenile collected in the northern Gulf 

 in August, almost certainly represented 

 an aberrant occurrence, or a case of 

 incorrect collection data, since the 

 northward migration ofspent adult blue- 

 fin through the Straits of Florida ceases 

 before the end of June (Rivas 1954, 

 Mather 1 963a), and no adults of the 

 species have been recorded in the Gulf 

 of Mexico in late July or August, to our 

 knowledge. These same considerations, 

 and the fact that the authors did not list 

 the characters on which they based their 

 larval identification, also cast doubt on 

 Gorbuno va and Salabarria's ( 1 967) re- 

 ports of bluefin tuna larvae in the Gulf 



5'^ 



Q 14 



^ 1.0 

 §0.8 

 ^06 

 §04 

 §0.2 



JAN MAR APR MAY JUNE JULY AUG SEPT OCT 

 MONTH 



Figure 69. Seasonal variation in mean gonadal-somatic indices of western 

 Atlantic bluefin tuna greater than 100 kg (number offish indicated above bars) 

 (Baglin 1976). 



83 



