FISHERY BULLETIN: VOL. 79, NO 4 



Caudal lengths are variable in the sample men- 

 tioned, so that adding and subtracting one stan- 

 dard deviation from the average ratio of caudal to 

 precaudal lengths gives Lcaudal = 0.829 or 0.987 



Lprecaudal- Total length given as Ltotal = Lprecaudal 



+ 0.908 (0.829 or 0.987) Lprecaudal- Using the 

 minimum and maximum ratios of caudal to pre- 

 caudal lengths, Guitart Manday's largest bigeye 

 thresher was estimated to be 434-471 cm long, and 

 Grey's 439-477 cm long. 



A bigeye thresher (SHO-16-2) reported by 

 I. Nakamura (pers. commun. to S. Kato^) had a 

 precaudal length of 227.2 cm, a dorsal 

 caudal length of 233.5 cm, and a total 

 length (precaudal + dorsal caudal lengths) 

 of 460.7 cm; using Guitart Manday's equation, its 

 precaudal length corresponds to a weight of about 

 245 kg. Still well and Casey (1977) and Cadenat 

 (1956) also measured bigeye threshers of about 4 

 m TL. However, most adults, especially males, fall 

 below 350 cm TL. 



Bigelow and Schroeder (1948) reported a 5.5 m 

 TL bigeye thresher from Cuba, apparently based 

 on data associated with a set of jaws in the 

 collection of Museum of Comparative Zoology, 

 Harvard. It is likely, as Bass et al. (1975) pointed 

 out, that this figure considerably overestimates 

 the maximum size of this shark. The tooth size 

 from Bigelow and Schroeder's (1948) "5.5 m" 

 specimen corresponds almost perfectly to that of a 

 363 cm TL shark examined by Bass et al. (1975), so 

 that, in the absence of contrary data, the total 

 length of Bigelow and Schroeder's largest speci- 

 men should be revised downward to about 360 cm. 



The average size of adult females of A . super- 

 ciliosus is larger than males. Guitart Manday 

 (1975) stated that females are always the largest 

 bigeye threshers caught on longlines, many ex- 

 ceeding 250 kg, and averaging 203.8 kg in 

 a sample of eight adults; but males are much 

 smaller, averaging 185.3 kg in a sample of four 

 adults. Stillwell and Casey (1976) reported that 25 

 females ranged up to 399 cm TL, while the 15 

 males they examined never exceeded 352 cm TL. 

 However, the mean length of females was only 5 

 cm greater than that of males. This similarity in 

 average total length resembles a condition noted 

 by Springer (1960) for certain carcharhinid and 

 sphyrnid sharks, in which a small percentage of 

 females in a population grow to a much larger size 

 than most of their sex and species. 



"Susumu Kato (see footnote 3), pers. commun. to L. J V. 

 Compagno, 1978. 



The longest known adult male bigeye thresher 

 shark was 378 cm TL (LACM-F-88),^ from off 

 California, and the smallest was 270 cm, from off 

 Portugal (Telles 1970). The longest known adult 

 females are the two of 399 cm TL and about 400 cm 

 TL reported by Stillwell and Casey (1976) and 

 Cadenat (1956) from the western North Atlantic 

 and Senegal, and the shortest two of 355-356 cm 

 from the western North Atlantic (Stillwell 

 and Casey 1976; specimen from Miami, Fla.). The 

 heaviest bigeye thresher reported ( Guitart Man- 

 day 1975), was a female, presumably mature, and 

 probably over 4.3 m TL (see above). 



The smallest free-living bigeye thresher re- 

 ported to date is a 130 cm TL immature male from 

 off Cuba (Bigelow and Schroeder 1948). Guitart 

 Manday (1975) reported a 144 cm TL free-living 

 individual that weighed 6.7 kg, while Stillwell 

 and Casey (1976) captured a 155 cm TL immature 

 male. We report here a specimen from North 

 Carolina of 159 cm TL. Bigelow and Schroeder 

 (1948) and Osipov (in Gubanov 1979) suggested 

 that parturition occurs in A. superciliosus when 

 the fetus attains 64 cm TL, but Cadenat (1956), 

 Nakamura (1935), and Gubanov (1979) reported 

 fetuses respectively at 68, 73, and 100 cm long. 

 Bass et al. (1975) suggested that the most likely 

 size at birth is 100-103 cm TL. Gubanov noted the 

 possibility that larger females might give birth 

 to larger offspring, a possible explanation of 

 the discrepancy of size at birth given by 

 various authors. 



Based on available data, the maximum accu- 

 rately measured total length for A. superciliosus 

 is 4.61 m, and weight, 284.5 kg, with total lengths 

 of 4.7-4.8 m and weights of 290+ kg not unlikely. 

 Apparently this species averages smaller in size 

 than at least some populations of A. vulpinus, in 

 which females in the western North Atlantic 

 reach 479-549 cm TL; the maximum size for A. 

 vulpinus may be over 609 cm TL (Bigelow and 

 Schroeder 1948; Bass et al. 1975). 



AGE AND GROWTH 



The age of a bigeye thresher has never been 

 determined by standard methods such as analysis 

 of vertebral rings. However, age and growth in 

 other shark species have been investigated by 

 several techniques (i.e., Petersen method, tag- 

 ging, growth in captivity) and found generally to 



"Grey's (1928) 4 m bigeye thresher appears to be a male in the 

 published photograph, but the article does not mention the sex. 



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