NATURAL HISTORY OF THE SANDBAR SHARK 



not well known and possibly are incompletely de- 

 fined. Minor differences between Atlantic and 

 Gulf of Mexico populations of E. ohscura need 

 further study. There is no difficulty, however, in 

 distinguishing E. milherti from these species or 

 from other species of sharks ordinarily found 

 within its geographical range. 



The importance of determining the presence or 

 absence of a middorsal ridge (a low ridge in the 

 skin extending for all or a part of the distance 

 between the first and second dorsal fins) for the 

 identification of carcharhinid sliarks cannot be 

 overemphasized. This minor structural feature 

 is certainly nonadaptive and its usefulness as an 

 indicator of probable relationships should be 

 great (see Springer, 1950: p. 1, and Backus, 

 Springer, and Arnold, 1956: p. 180, for discus- 

 sion). The first mention of this characteristic in 

 publislied work was by Nichols and Breder 

 (1927), but correct identifications of tlie common 

 large ground .sharks of the east coast of the 

 ITnited States were made by Nichols and by Rad- 

 cliffe independently before lOlfi. 



In one of the more valuable papers on sharks, 

 Radcliffe (1916) made the first general use of the 

 structure of the dermal denticles to show differ- 

 ences in western North Atlantic carcharhinid 

 species; and his illustrations show clearly the 

 distinctive denticle type and arrangement which 

 sets E. m/'lberti off from other carcharhinids 

 within its range, except for the newly described 

 E. alt I ma. Both E. miJberti and E. aJtima differ 

 from all other North American carcharhinid 

 sharks in having nonimbricate denticles without 

 strongly projecting points; however, the denticles 

 of E. ultima are mucli smallei- tlnin tliose of 

 E. 7nUherti. 



Commercial shark fishermen at Salerno and Kej* 

 West, Fla., recognized altlma as distinct from the 

 sandbar .shark and called it the bignose .shark or 

 Knopp's shark before it received a scientific 

 name. The diagnosis given with the original de- 

 scription of E. althna (Springer. 1950) should 

 be adequate for the determination of specimens 

 of all sizes. All of the known examples of E. 

 nltima have been taken at depths of 50 to 150 

 athonis off Salerno, Florida, in the Straits of 

 Florida, in the northeastern Gulf of Mexico, and 

 n the Dragon's Mouth between Trinidad and 

 Venezuela. Its vertical range overlaps that of 



tiie shallower water E. milberti in the Straits of 

 Florida aiea and extends well into the nighttime 

 range of tlie night shark. Ilypapnon signatus 

 Poej'. The geographical range of E. altlma may 

 be quite extensive, but it is unknown because 

 comparatively little fishing has been carried out 

 at the depths whei-e this species might be expected 

 to occur. Such fisliing as has been done in mid- 

 water and just beyond the edges of the Conti- 

 neTital Shelf by connnercial shark fishermen indi- 

 cates that the species is relatively common. 



Probably many more E. altima would have 

 been taken by the connnercial fishery were it not 

 for the fact that in the Florida-Caribbean region 

 the liver oil of althna is characteristically lower 

 in vitamin-A content than is that of any of the 

 other species of Eulamio or of Hypo prion in that 

 area. 



In a large measure, the confusion in the nomen- 

 clature of the larger American carcharhinids that 

 existed before tlie publication of the 1948 work 

 by Bigelow and Schroeder would undoubtedly 

 have been avoided if descriptive literature had 

 included information on tlie presence or absence 

 of the middorsal ridge. A fine replica of a shark, 

 wliicli in the light of the better descriptions now 

 available can easily be identified as Carcharhinvs 

 leucas (Midler and Henle), a species without a 

 middorsal ridge, is shown in an illustration in an 

 informative article (Rockwell, 1916: p. 161) 

 under the caption Carcharhinus obscurus {Eula- 

 inia obseura), a species with a middorsal ridge. 

 Determination of the presence or absence of the 

 ridge is sometimes difficult, particularly for mu- 

 .seum specimens or for specimens that have been 

 exposed to the sun for a long period. Although 

 identifications can be made without reference to 

 the ridge, they are likely to be difficult and use 

 of all of the available ditferentiating character- 

 istics is desirable. 



The confusion of the sandbar shark with the 

 bull shark extends to the Pacific. References 

 liave fi-equently been made to tlie sandbar shark. 

 Eulamiii milherti, as occui'ring on the Pacific 

 roast of Panama. There is no evidence of this 

 and tlie species probably is not found there. Gar- 

 man's (1913) synonymy of milherti included 

 Eulamia nicarafjuensifi (till and Bransford, the 

 fresh-water bull shark. The two bull sharks. 

 nicaraguensis and leucas are so similar to one 



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