NATURAL HISTORY OF THE SANDBAR SHARK 



23 



rlie e<rg.shell membriuie. but i% notes do not indi- 

 cate at what point the pseudoplacenta functions 

 outside of tlie shell inenihrane. The anioimt of 

 clear fluid within the shell increases as the em- 

 bryo grows. It is present at the time the embryo 

 reaches the approximate size at which the young 

 are born — 24 inches in the Florida area. Exter- 

 nal gills were noted on embiyos up to about -1 

 inches but were absent on 41^- to 5-inch embryos. 

 Some 3'olk was found remaining in the pseudo- 

 placental apparatus in embryos that had reached 

 a size of 12 inches, but yolk material was entirely 

 absent from the well-developed, yolk-sac placen- 

 tal apparatus of embryos 15 inches long. As the 

 embryo grows, the yolk or attachment of the 

 pseudoplacenta lengthens. In E. milherti and in 

 other western North Atlantic Eidamia the yolk 

 stalk has no structural embellishments a^t^ any 

 stage in its development insofar as I-ha'^e-liTOeii 

 able t« discovec^ Structures of this kind occur 

 in , some species of hammerhead. Sphyrna, but 

 differ in the various species. When embryonic 

 E. milherti are near full term the stalk (pseudo- 

 placental attachment) is easily broken at the 

 point of attachment to the embiyo. The scar of 

 this attachment remains clearly visible until the 

 young shark has attained an inch or more of 

 postnatal growth, '"''•^^'^''^i '^'' ^^■'^, 



iNormaliy the large eggs in the ovary of E. 

 milherti are bright yellow; but white eggs, sug- 

 gesting some pathological condition, were found 

 a few times in the fall. "White eggs were noticed 

 less frequently in E^-miTberti, however, than in 

 EuJamia obscvra, Carcharhimus Jeucas, or Sphyma. 

 sp. In these last three species, white eggs 

 were noticed in exceptionally large sharks {E. 

 ohscura and Sphryna sp.) and deformed sharks 

 (lcu^a.'i).\ 'So excessively large deformed or 

 obviously diseased milherti were seen in ex- 

 aminations of many hundreds of adult fe- 

 males. Dead embryos were noted occasionally 

 but not frequently in E. milherti and these were 

 generally 10 to 15 inches long, that is, at about 

 tlie size at which the egg yolk would be com-  

 pletely absorbed. The dead embryos sometimes '■ 

 ajipeared to be dehydrated but there was no 

 noticeable putrefactive decomposition. _ 

 Number of young in litter , , 



In an earlier publication (Springer, '1940),*' I 

 reported the collection of 13 litters of Eulamia 



inillerti pups from Englewood, Fla. In this lot 

 59 were males and 63 were females. Another 

 series of 28 litters from the west coast of Florida 

 had 130 males and 130 females. A third series 

 of 24 litters from the east coast of Florida in- 

 cluded 116 males and 112 females. The number 

 of embryos in each litter varied from 1 to 14 but 

 the modal number was 10 and the average num- 



ber was 9. 



'^? , 



The available data do not show an increase in 

 the number of young with increased size of the 

 mother as repozled for some other genera 

 (Backus et al., 1956). In Eulumia milberti, 

 however, the size range of adult females is not 

 great and such a correlation, if it exists, would 

 be difficult to demonstrate. 



Species of Eiilamia taken in the Florida region 

 other than inilberti all frequently carry 10 em- 

 bryos to full term. The average number of em- 

 brj'os to the litter for these other species is less 

 than 9, which is the average litter number for 

 E. milherti. All of the other Florida species of 

 Eulamia are somewhat larger than milherti and 

 the largest species. - Eidam,ia ohscura, " has the 

 smallest average number of embryos to the litter. 

 In E. ohscura, pups were often found only in one 

 of the oviducts. This suggests the possibility 

 that fertilization was effected only through one 

 .^viduct. Various other observations on the loca- 

 " tion and numbers of embryos in E. ohscura and 

 other Florida Eulamia lead to the conclusion 

 that the normal maximum [usual] number of 

 young in each species is 10 plus or minus 2, but 

 that actual numbers are progressively smaller the 

 larjjer the mother. 



Length of young at birth 



Consideration of all of the available data 

 places the time of birth from March to early 

 August and the size at birth from 17 to 25 inches. 

 The length at birth of 24 inches seems, however, 

 to be the best estimate for the young born in 

 northern Florida waters. Smaller young and a 

 somewhat later birth date may be characteristic 

 ,- of the part of the population in cooler waters. 

 An estimate of (he gestation period based on 

 southern Florida specimens is 9 months with lim- 

 its of the estimate 8 to 12 months. Some varia- 

 tion might reasonably be expected to result from 

 ditl'erences in water temperature during devel- 

 opment. 



( Aj~,'< I,, 



