NATURAL HISTORY OF THE SANDBAR SHARK 



31 



mny rise sharply as the shark becomes sexually 

 mature but this does not affect tlie ceneral trend 

 in the total amount of vitamin A stored. Fluc- 

 tuations in the amounts of oil stored in the liver 

 may normally accompany such events as young 

 bearing, mating, and periods of poor feeding, 

 and these fluctuations apparently affect potency, 

 but the total amount of vitamin A is subject to 

 fluctuation to a lesser degree. It has been shown 

 for Galeorhinus zyopteiiis of the Pacific coast 

 (Ripley and Bolomey. 1946) that the total 

 amount of vitamin A in the largest males and 

 largest females does not greatly differ. 



Livers of Squahis siiehlei/i of the Pacific coast 

 have a higher average vitamin-A potency than 

 livers of Sqiuilus acanthias of the Atlantic. The 

 two species are morphologically so similar that 

 taxonomists have had doubts about their separa- 

 tion. Concerning the differences in liver oil po- 

 tency. Templeman (1944) has the following com- 

 ment : 



Whether the greater length of the mature Squalus 

 surklii reflects a greater age or a greater growth rate 

 than those of Squalus acanthias is not known, but this 

 greater size is possibly partly responsible for the higher 

 vltamin-A value of its liver oil. 



The greater vitamin-A content of shark livers 

 does not always occur in the larger individuals 

 in a given species. For example, my own meas- 

 urements and assays show that 0. l-eucas off the 

 mouth of the Mississippi River average appre- 

 ciably longer and heavier than C. leucas taken 

 off the mouth of the Orinoco River; but the liver- 

 oil potency of the species from the vicinity of 

 the Mississippi River mouth is extremely low, 

 while that of the C. leiicas from the vicinity of 

 the Orinoco is high. These differences are quite 

 great and reasonably constant. Adult male f. 

 leucas from the Orinoco area have liver-oil po- 

 tencies above .50,000 I.U./gm. (international units 

 per gram uncorrected for irrelevant absorption), 

 while adult males from the Mississippi area gen- 

 erally have liver-oil potencies of 1,000 to .5.000 

 I.U./gm. Variation in liver-oil potency liy area 

 is perhaps greater in C. leucas than in most shark 

 species of the northwestern Atlantic, but the vari- 

 ation is appreciable in all .species. 



A rough classification by regions of part of the 

 northwestern Atlantic on the basis of shark-liver 



vitamin-A potency from data assembled by the 

 shark fishery is as follows: 



Extremely low potencies — Gulf of Mexico; low 

 potencies — northern Bahamas and shallow-water 

 areas of the West Indies; intermediate potencies 

 — Carolina coast, east coast of Florida, and coast 

 of Cuba; high potencies — .southern Caribbean, 

 coast of Costa Rica to the Guiana coasts. To 

 a limited extent this classification is useful to 

 trace probable origins of elements of migratoi-y 

 stocks. Potency differences among liver oils taken 

 from single adult specimens of EuJamia milberti 

 were in the range from about 2,500 to 25,000 

 I.l"./gm. One exception was noted in that one 

 assaj' (the only one available) on mixed E. mil- 

 berti livers from the coast of Nicaragua-Costa 

 Rica was substantially higher, about 38,000 LIT./ 

 gm. 



If E. milberti from the coast of Nicaragua- 

 Costa Rica returned regularly to the species* At- 

 lantic population center from Florida northward, 

 some among the hundreds of livers of milberti 

 taken at Salerno, and assayed separately should 

 have had potencies greater than 38.000 I.U./gm. 

 None had such a high potency. 



The average potency of oil from livers of Eu- 

 lamia milberti w'as found to be substantially 

 lower from the southwest coast of Florida tlian 

 from the southeast coast although the extremes 

 in individual potencies were about the same. 

 Since both stocks have a common origin from the 

 Atlantic coast north of Cape Canaveral we might 

 assume that the difference in averages results 

 from either the lower age of the adult milberti 

 reaching the west coast of Florida or a lower 

 rate of vitamin-A accumulation due to the period 

 spent in the Gulf of Mexico, or from both of 

 these. 



The liver-oil potency of the eight adult female 

 E. milberti from the mouth of the Mississippi 

 River was higher and the total vitamin A from 

 these sharks was about the amount to be ex- 

 ])erted from similar sharks taken on the east 

 coast of Florida. This potency would be ex- 

 l)ecte(l only if these sharks originate outside of 

 the Gulf of Mexico. 



To the extent that data on vitamin-A potency 

 determinations have any validity for the deter- 

 mination of age or the areas of origin of migra- 

 tory stocks, they support the general conclusions 



