26 



FISHERY BULLETIN OF THE FISH AND "WILDLIFE SERVICE 



adult females taken in winter off Englewood, on 

 the west coast of Florida, were pravid. I saw 

 large numbers of E. miJherti in 1942 and again 

 iiovn 1946 through 1949 at Salerno, and my notes 

 include several estimates of the proportion of 

 gravid to nongravid adult females seen on the 

 dock. For the late-winter and early spring 

 periods, it was estimated that substantially less 

 than a third of the females were carrying pups.' 

 In n^ sani]ile of 399 adult females takeri' for 

 length-frequency data, apjuoximately 18 percent 

 were gravid. 



Three interesting, if theoretical, explanations 

 are suggested to account for the apparent differ- 

 ences in the number of males and females in 

 milherti and in other Enlamia. 



Tlie mating pattern appears to be particularly 

 dangerous to the males, since mating occurs when 

 the females are in a feeding cycle while the males 

 ai-e not. That is, during courtship males may nip 

 or slash to some extent but do not take large 

 bites. The females have no such inhibitions ex- 

 cept at the time the young are born, and fatal 

 accidents to males may be frequent during court- 

 ship. However, if this explanation is to be ac- 

 ceptable, some further speculation is needed to 

 suggest why Galeocerdo with a similar mating 

 pattern is not represented in the adult population 

 by a preponderance of females. 



Geiser (1924) summarized a variety of reports 

 on the higher death rate for males in some mam- 

 mals, fishes, and invertebrates, and suggests that 

 there is a genetic basis for this in certain cases 

 wliere the possession of two sex chromosomes by 



the females 



ensures a greater lonerevitv of 



the female by "canceling out" possible mutations 

 in the x-chromosome, especially associated lethals. 

 while in the male there is no such "canceling 

 out."' 



The third explanation is that the males occupy 

 wider geographical and vertical ranges than the 

 females, remain in the cooler parts of the ranges, 

 and exhibit a greater tendency to wander than 

 the females. Thus, greater numbers of males 

 than females are lost to the breeding population 

 by wandering and death in unfavorable environ- 

 ments. 



Whatever the explanation for the unequal sex 

 ratio, the smaller number of males is not a suffi- 



cient handicap to prevent E. milberti from being 

 one of the conunoner sharks. 



GROWTH AND SIZE AT MATURITY 



In Florida catches, adult male Eulamia mil- 

 herti average 4.2 inches shorter than the average 

 1 adult female and weigh 32 pounds less than the 

 ,' average nongravid adult female. The smaller 

 size of the adult male is characteristic of all of 

 the western North Atlantic carcharhinids al- 

 though the size of males and females at birth is 

 approximately the same. For about 20 years I 

 maintained a clo.se watch oji landings of one 

 or more commercial vessels and saw \io mUherti 

 females longer than 92 inches and no males longer 

 than 89 inches among the thousands that were 

 examined. ^ 



The smallest sexually mature male in the ma- 

 terial examined was 71 inches and the smallest 

 sexually mature female was 72 inches in total 

 length. Sexual maturity in the male is easily 

 and {lositively determined because enlargement of 

 the testes to functional size is immediately fol- 

 lowed by the appearance of a ring of calcium at 

 the surface of the major clasper cartilage. This 

 ring is easily seen in cross section but since its 

 effect is to stiffen the segments of the clasper, 

 sectioning is unnecessary for positive determina- 

 tions. Determination of sexual maturity in fe- 

 male specimens where the specimens were non- 

 gravid or had no courtship scars was made by 

 examination of the ovary and -the oviducts. The 

 females were regarded as sexually immature if 

 none of the eggs in the ovary had l)egun to increase 

 in size and if the oviducts were smaller in diame- 

 ter than is characteristic of the ftilly contracted 

 ovi^ ducts in females following jiarturition. It 

 may be noted in table 6 that, while at least 2 

 female milherti were mature at a length of 72 

 inches. 5 immature females of greater lenglh were 

 collected. Obviously the length at which the fe- 

 males may become sexually mature varies more 

 tlian 4 inches. 



The left skew of the length-freiinency polygons 

 shown in figure .5 may be the result of any of sev- 

 eral variables including the length at wjiich 

 maturity is reached. 



A total of 513 adult sandbar sharks was select- 

 ed from southeastern Florida catches for meas- 

 urement of total length and for comparison of 



