FISHERY BULLETIN: VOL. 80, NO. 1 



though these two spawning grounds have been 

 well documented, a question remains whether 

 bluef in tuna spawn elsewhere and at other times. 

 Mather 4 believes that some bluefin tuna prob- 

 ably spawn in late spring near the northern edge 

 of the Gulf Stream off the eastern United States. 

 Berrien et al. (1978) have reported collecting 

 bluefin tuna larvae from this area during April 

 and June 1966. These larvae, however, could 

 have drifted to this area from spawning grounds 

 farther south. 



In this paper, I describe bluefin tuna ovaries 

 from the Middle Atlantic Bight (the U.S. coastal 

 area between Cape Cod and Cape Hatteras) and 

 examine the possibility that this may be another 

 significant spawning area for bluefin tuna. Also, 

 I make some comparisons of female gonadal 

 development between the known spawning 

 areas. 



My literature review on bluefin tuna shows 

 there is a need for additional information on the 

 bluefin tuna's reproductive potential. A wide 

 range in fecundity estimates was found. Frade 

 (1950) reported that an eastern Atlantic 160 kg 

 bluefin tuna produced 18.7 million eggs. 

 Williamson (1962) stated that the ovaries of a 

 272.4 kg western Atlantic bluefin tuna con- 

 tained about 1.0 million eggs. Rodriguez-Roda 

 (1967) estimated that off southern Spain a 54 kg 

 fish could produce 5.5 million eggs and a 235 kg 

 bluefin tuna could produce over 30.0 million eggs. 

 Baglin (1976) estimated that a 188.4 kg western 

 Atlantic bluefin tuna could produce 16.7 million 

 eggs and that a 271.5 kg bluefin tuna could 

 produce 31.4 million eggs. Baglin and Rivas 

 (1977) indicated that a 324 kg western Atlantic 

 tuna could produce 57.6 million eggs. I deter- 

 mined the fecundity of bluefin tuna taken from 

 the United States sport fishery in the Florida 

 Straits and Gulf of Mexico and from the 

 Japanese longline fishery in the Gulf of Mexico 

 and compared my findings with previous 

 estimates. I have also examined monthly sex 

 ratios for western Atlantic bluefin tuna. 



MATERIALS AND METHODS 



Bluefin tuna from the Gulf of Mexico, Florida 

 Straits, Middle Atlantic Bight, and off the 

 northeast coast of the United States were 



sampled from anglers' catches. Bluefin tuna 

 samples from purse seine catches came from the 

 Middle Atlantic Bight and the northeast coast of 

 the United States. Bluefin tuna were also 

 sampled from the Japanese longline fishery in 

 the Gulf of Mexico and from the New England 

 handgear fishery. 



Throughout this paper the classification 

 system of Rivas (1979) was used. Thus, small 

 bluefin tuna are 50-129 cm fork length (FL) and 

 3-44 kg round weight, medium bluefin tuna are 

 130-180 cm FL and 45-130 kg round weight, and 

 giant bluefin tuna are >180 cm FL and >130 kg 

 round weight. 



Sex data were obtained from 283 small and 

 medium bluefin tuna captured by commercial 

 and sport fishermen off the Middle Atlantic 

 Bight (1974-77). Also, sex data were obtained 

 from 3,429 giant bluefin tuna captured by sport 

 and commercial fishermen in the Gulf of Mexico 

 and along the northeast coast of the United 

 States from North Carolina to Maine, and from 

 fish taken by sport fishermen in the Bahamas 

 (1975-78). 



Straight fork length (cm) was measured with 

 calipers and round weight was recorded in 

 pounds and later converted to kilograms. In 

 some instances where either weight or length 

 was unknown, a functional regression (Baglin 

 1980) was used for estimating the missing 

 measurement. 



Small and medium fish were assigned an age 

 based on a length-weight-age conversion table 

 presented by Coan (1976). No ages were assigned 

 to giant fish because of the difficulty experienced 

 in aging them accurately. 



Ovaries were examined from 81 small and 

 medium bluefin tuna caught from 1974 through 

 1977 and from 403 giant bluefin tuna collected 

 during 1965 through 1968 and 1974 through 

 1978. Ovaries were stored in 10% Formalin 5 and 

 later blotted dry and weighed in grams. The 

 gonosomatic index (GSI) (ovary weight as a 

 percentage of total body weight) was used as a 

 gross indicator of maturity. Only fork length was 

 taken from Japanese longline samples from the 

 Gulf of Mexico for which the GSI was calculated 

 using an estimated body weight from the length- 

 weight relationship of Baglin (1980). 



A detailed examination of ovaries from 292 



"Mather. F. J., III. 1973. The bluefin tuna situation. Proc. 

 16th Annu. Int. Game Fish. Res. Conf., p. 93-120. 



5 Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



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