NATURAL HISTORY OF THE SANDBAR SHARK 



27 



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20 



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72 74 76 78 80 82 84 86 88 90 

 TOTAL LENGTH IN INCHES 



Figure 5. — Length-frequency polygons for adult male and 

 female Eulamia milberti from southern Florida. 



leno^h frequency with the length frequencies 

 of 76 sharks from off Fort Myers on the west 

 coast of Florida and of 51 sharks from the Carib- 

 bean coast of soutliern Nicaragua and northern 

 Costa Kica (table 6). To reduce bias, all sharks 

 of all species in any catcli were measured and 



recorded or none were recorded. Selection was 

 affected by the scarcity of males. The compara- 

 tively large sample of fall females at Salerno had 

 to be measured to get any catches that included 

 males which rarely appeared there at that season. 

 In the sample taken from the lower east coast of 

 Florida, 10 sharks, o males and 5 females, were 

 found to be immature. These immature shark.s 

 were excluded from the calculations of mean 

 lengths of adults, but the sizes together with the 

 dates of capture are given in footnotes to table 6, 

 which shows the mean length of tlie sample lots. 



By its migratoiy movements and its restriction 

 to limited nursery areas, the North American 

 population of E. milherti appears to be subject 

 to constant mixing. It does not seem reasonable 

 to expect a rigid segregation by area of origin of 

 those milberti mating off southern Florida. This 

 may be one factor in the apparent homogeneity 

 of the population. 



In some of the other caicharhinids, environ- 

 mental or racial factors appear to affect the size 

 at which the species becomes mature. For ex- 

 ample, the average size of the bull shark. Car- 

 charhmus leiicas. from the A'icinity of Trinidad 

 is appreciably less than the average size of adults 

 of the same species from the Gulf of Mexico. 

 Important differences in tlie size at maturity as 

 well as the size at birth separate-tl*^ Texas and 

 southei-n Floi-ida ]>opulations of the little black- 



Table 6. — Mean length, number measured, and length range of adult Eulamia milberti, by sex, area, and season of collection 



' .5 immature males were collected with thus sample but excluded from tabulation and from calculations of mean length: I specimen 64 inches long collected In 

 .March. 2 specimens each 66 inches long collected in .\ugust. 1 specimen 5'j inches lone collected in Octoher. and 1 specimen 6S inches long collected \n November. 



- .5 immature females were collected with this sample but e\clude<l froni l:ibulalion and from calculation of mean lengths: 1 s|»eclinen 72 inches long collected 

 In .January, 1 specimen 76 inches long collected in .\pril. I specimen 73 inches long collected in Juiv, and 2 specimens collected in October of which I was 75 

 Inches long and tlie <ither 76 inches. 



' From preceding collections. 



