3 BIONOMICS AND LIFE HISTORY 

 3.1 Reproduction 

 3.11 Sexuality 



The species is heterosexual. No occurrence of her- 

 maphrodism or intersexuality has been observed. 

 Males and females are indistinguishable externally, 

 but the females attain a much larger size than the 

 males. 



For the central Pacific, Royce (1957) indicated that 

 females have been taken at weights greater than 727 

 kg (1,600 lb) whereas the largest male weighed only 99 

 kg (218 lb). Around Hawaii most of the males weigh 

 between 45 and 91 kg (100 and 200 lb), whereas most 

 of the females weigh between 91 and 227 kg (200 and 

 500 lb) (Strasburg, 1970). In Puerto Rico, the largest 

 male examined by Erdman (1968) weighed 135 kg (297 

 lb) and the largest female 370 kg (814 lb). Data from 

 the Japanese longline fishery show that males seldom 

 exceed 116 kg (255 lb) and that most males weigh 

 from 39 to 80 kg (85 to 175 lb). De Sylva (1963) record- 

 ed a 140-kg (308-lb) male from Bimini, Bahamas, and 

 Strasburg (1970) recorded a 133-kg (293-lb) male from 

 Hawaii. Of 30 blue marlin examined by me in the 

 northwestern Atlantic, 18 were males weighing 46 to 

 94 kg (101 to 207 lb) and 12 were females weighing 59 

 to 277 kg (130 to 609 lb). Usually, a blue marlin 

 heavier than 136 kg (300 lb) is a female. 



According to de Sylva (1963) protandry, the condi- 

 tion whereby a fish begins its life as a male and sub- 

 sequently changes into a female, has been considered 

 for the blue marlin. 



3.12 Maturity 



The age at which sexual maturity is reached cannot 

 be calculated because methods of age determination 

 have not been developed. As already indicated, males 

 are smaller than females and size has to be con- 

 sidered. The smallest sexually mature male reported 

 by Erdman (1968) from Puerto Rico weighed 35 kg (76 

 lb) and the smallest ripe male reported from Jamaica 

 by de Sylva (1963) weighed 44 kg (97 lb). Of 26 males 

 from the central Pacific examined by Royce (1957) the 

 smallest specimen found with milt in the central duct 

 of the testes weighed 42 kg (93 lb). The smallest sex- 

 ually mature male reported for the western Indian 

 Ocean by Merrett (1971) weighed 41 kg (90 lb). The 

 smallest sexually mature female reported by Erdman 

 (1968) from Puerto Rico weighed 61 kg (135 lb) and 

 the smallest mature female reported by Merrett 

 (1971) from the western Indian Ocean weighed 47 kg 

 (103 lb). Of 1,152 females studied by Kume and 

 Joseph (1969b) from the eastern Pacific, the smallest 

 specimens found in a condition believed to be near 

 spawning were about 200 cm long (eye to fork; no 

 weight given). The indications are, therefore, that 

 males reach sexual maturity at a weight of 35 to 44 



kg (76 to 97 lb) and females at 47 to 61 kg (103 to 135 

 lb). 



3.13 Mating 

 Probably polygamous. 



3.14 Fertilization 



Evidence indicates that fertilization is external. 



3.15 Gonads 



The relation of gonad weight to body weight was 

 determined by Erdman (1968) for 14 males and 15 

 females from Puerto Rico. Males weighed from 47 to 

 123 kg (103 to 270 lb) and their testes from 55 g to 2.4 

 kg (0.12 to 5.30 lb). Females weighed from 33 to 292 kg 

 (72 to 643 lb) and their ovaries from 9.1 g to 6.5 kg 

 (0.02 to 14.2 lb). The weight of the testes, as the per- 

 cent of body weight, ranged from 0.10 to 2.30% in the 

 males and from 0.03 to 3.60% in the females. Accord- 

 ing to Erdman less than 0.10% for the testes and 

 ovaries corresponds to sexually immature individuals. 

 In the males, 0.10% to less than 0.70% corresponds to 

 the developing stage with few to many spermatocytes 

 and few or no sperm. Prespawning stage corresponds 

 to a range of 0.70% to less than 2.30% with many sper- 

 matocytes and many sperm. At the ripe stage the 

 relative weight of the testes decreases to a range of 

 0.60% to less than 1.60% but with few or no sper- 

 matocytes and many sperm. At the postspawning 

 stage, 0.10% to less than 0.20%, there are no sper- 

 matocytes but many sperm. In the females, 0.10% to 

 less than 1.0% corresponds to the developing stage 

 with oocytes and no ova or a few developing ones, but 

 no easily visible eggs. The subripe stage corresponds 

 to a range of 1.00% to less than 3.60% with advanced 

 oocytes and pale-yellow eggs. At the ripe stage the 

 weight of the ovaries decreases to less than 1.50% of 

 body weight, but is still 1.00% or more, with advanced 

 oocytes, transparent eggs, and some postovulatory 

 follicles. At the postspawning stage, 0.50% to less than 

 1.00%, there are some atretic bodies, many empty 

 follicles, and degenerating oocytes. 



Krumholz (1958) gives a range of 0.80 to 1.90%, 

 with an average of 1.43%, for the weight of testes in 

 relation to body weight in blue marlin from the 

 Bahamas. 



The relationship between ovary weight and body 

 length for 1,152 blue marlin from the eastern Pacific 

 was given by Kume and Joseph (1969b). Ovary 

 weights ranged from a few grams to 14 kg (31 lb) and 

 lengths (eye to fork) from about 140 to about 338 cm. 

 In the majority of specimens the ovaries weighed less 

 than 1 kg (2.2 lb) and probably were not in a spawning 

 condition. 



The length of the gonads, as a percentage of body 

 length, can be used as an index of sexual maturity of 



