30 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



and body. These organs, which perform a func- 

 tion correspondinji to taste, have been described 

 in detail by Budker (1938). Under ordinary 

 circumstances the testing procedure is routine for 

 objects which are not moving or which are not 

 part of a series of similar-appearing objects, one 

 of which has already proved edible. The pro- 

 cedure may be omitted if there is competition for 

 food. 



It seems improbable that the sensory crypts 

 of the head function in any other way than as 

 gustatory organs. To find suitable food or to 

 find an area having food in it, Eiilamia milberfi 

 as well as many other species depends on olfac- 

 tory organs. Experiments by Parker and Shel- 

 don (1913) with Mustelws canis probably outline 

 the general pattern of behavior of the cachar- 

 hinids in their search for food. 



Carcharhinid sharks in general are opportun- 



w , ists in feeding aBd_neeessarily-s©i-. Without spe- 

 / cial techniques, developed in some species but not 



**^ to my knowledge in Eidamia milherti^ sharks 

 are relatively ineffective at catching uninjured 

 fish in open water or even at finding such slow- 

 moving objects as crabs. The shark's ability to 

 exist on a I'egimen of feast and famine, imposed 

 by its ineptness in catching food at will, is prob- 

 ably made possible through its unique digestive 

 and fat-storage organs. A general outline o:f the 

 processes of digestion and fat storage by sharks 

 is beyond the scope of this report. It is pertinent 

 to point out that their digestion is rapid and 

 thorough, and that the shark's liver with its high 

 percentage of oil is a good index of its meta- 

 bolic well-being. The larger, fatter livers are 

 found in sharks in good condition while small 

 livers with little oil are frequently found in 

 sharks having severe injuries, sharks in obviously 

 [ poor condition, or in the males at the end of the 

 mating season. 



The liver of adult E. mUherti typically repre- 

 sents between 10 and 15 percent of the animal's 

 total weight, rarely more than 18 percent and 

 rarely less tlian 6 percent. The proportional 

 weight of the liver in adult E. mMherti males is 

 lower than in females, but the liver weight of the 

 species is remarkably uniform in comparison with 

 larger species of carcharliinids within its geo- 

 graphical range. This is strong evidence that 

 E. miJhfrf} is successful in getting an adequate 



supply of food regularly. Galeocerdo cuvier, 

 Carcharhinus leucas^ and Eulmnm ohscwra. all 

 species more than twice as heavy as milberti, 

 frequently have livers 25 percent or more of the 

 total weight of the fish. On the other hand, they 

 often have very small livers, as low as 3 percent 

 of the total weight. The inference is reasonable 

 that the larger species have greater difficulties 

 finding food, or more precisely, may have to wait 

 longer between meals. This inference from liver 

 weight also is consistent with the observation 

 that the foods of the larger species are frequently 

 of a less digestible type and may be taken as a 

 kind of desperation measure and certainly not as 

 a first choice. Galeocerdo, for example, fre- 

 quently fills its stomach with large horseshoe 

 crabs, huge horse conchs complete with shell, 

 or even old shoes and tin cans. 



Because of commercial interest in the vitamin- 

 A content of shark-liver oils that existed for a 

 number of years, a large amount of data is to 

 be found in the literature on the subject. Also 

 available to me are data on the oil and vita- 

 min-A content of livers of E. milherti taken at 

 Salerno. Some determinations for Salerno spe- 

 cies were given in an earlier publication 

 (Springer and French, 1944). Better methods of 

 estimation of the vitamin-A concentration in liver 

 oils came into general use later, but these did not 

 appreciably alter the general trends observed. 



The tendency in each species to an increase in 

 the vitamin-A concentration, or potency, of the 

 liver oil with the increase in size of that species 

 has been noted by many workei-s (Pugsley, 1939; 

 Brocklesby, 1941; Templeman, 1944; Ripley and 

 Bolomey, 1946, et cetera). The liver-oil vitamin- 

 A potency varies considerably. Each species and 

 locality produces sharks having potencies that are 

 approximately predictable. Characteristically, 

 in most species the males produce oil of some- 

 what higher vitamin-A potency than that of the 

 females, but they often have less oil in their 

 livers. 



An hypothesis which has general support is 

 again advanced here that within a given species 

 and locality, the total amount of vitamin A in I 

 the liver of a shark is roughly proportional to | 

 the age of the shark. Thus, the older the shark | 

 the greater is the total amount of vitamin A 

 in its liver. The rate of increase in vitamin A 



