34 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



No Eidamia except miJhert'i is known to have 

 nursery grounds within the geographical and 

 liabitat range of the bull shark. The nursery 

 ranges of E. altima and E. ohscura are well off- 

 shore in deeper water, E. floridana nursery 

 grounds are on otfshore banks where bull sharks 

 do not go, and bull sharks are uncommon at 

 least, or normally absent around reefs which are 

 nursery grounds for springer!. The sugges- 

 tion is advanced here that predation by the bull 

 shark is the chief reason, and perhaps the only 

 reason, for the scarcity of E. mUhert'i in the Gulf 

 of Mexico and southward in continental waters. 

 The comparatively few bull sharks of the Atlan- 

 tic coast may be presumed to act as a check on 

 the numbers of young E. milberfi, but without 

 disastrous effects for that species. 



Some interesting complications are associated 

 with predation of large sharks upon smaller ones. 

 Evidently all carcharhinid sharks will eat other 

 sharks sometimes if not regularly. However, it 

 is a shark fisherman's axiom that sharks left on 

 the line to spoil will burn out tlie fishing groiuids 

 and make it necessary to move away 5 miles or 

 so to continue fishing. A rationale has been 

 partly outlined in an earlier publication 

 (Springer, 1954) covering experiments with Mi/s- 

 tehix in tanks. Feeding of Mvsfelufi was entirely 

 inhibited in the presence of shark flesh that had 

 been allowed to stand at room temperature for 

 4 days. 



Presumably sharks have no difficulty digesting 

 sjiark flesh jirovided it is fresh. Although sharks 

 appear to be able to digest the partially decom- 

 posed flesh of other vertebrates, their digestive 

 processes are slowed or stopped completely wlien 

 tliey swallow large quantities of decomposing 

 sharks or rays. 



The flesh of sharks becomes strongly alkaline 

 during decomposition. The continuous liberation 

 of ammonia through action of enzymes produced 

 during the coui'se of ordinary putrefactive de- 

 composition on the urea that normally occuis in 

 sharks (see Smith, 19.36). seems effectively to 

 block, or at least to greatly retard, digestion. 

 The proteolytic enzymes of the shark's stomach 

 are most active in an acid medium (Sprissler, 

 1942). In my examinations of juices of shark 

 stomachs in the field, estimates were made of the 

 hydrogen-ion concentration, as .shown by indica- 



tor solutions. Juices from shark stomachs that 

 contained large amounts of shark flesh in obvi- 

 ously decomposing condition were found to be 

 substantially above pH 8.0, whereas juices from 

 shark stomachs containing fish, turtles, birds, or 

 small amounts of fi'esh shark were estimated at 

 pll 4.0 or below. It is not clear whether ex- 

 cessively large meals of decomposed shark flesh 

 produce any result more serious than delayed 

 digestion. 



I have not seen evidence that internal parasites 

 e\'er greatly damage Eulmnm milberti. Round- 

 worms in the stomach, roundworms and adult 

 tapeworms in the scroll-type intestine, and cope- 

 pods on the gills and external surfaces were 

 commonly seen. In comparison with other large 

 Florida sharks, mUherti seemed to be the least 

 troubled by parasites. Occasionallj% sharks taken 

 from lines apparently set in areas of extraordin- 

 ary abundance of a small isopod were found to 

 have a large proportion of the viscera eaten away 

 by swarms of the isopods. which had entered the 

 body cavity by way of the soft parts around 

 the anus. It has been assumed that these iso- 

 pods attack successfully only after the sliarks 

 die on the lines or at least have been restricted 

 in movement. Similar isopods attack living small 

 fishes and man (Springer. 19.57) and it seems 

 quite possible that they may also attack living 

 sharks. If they successfully attack living sharks 

 they may be one of the principal enemies of 

 sharks in temperate and tropical waters of shal- 

 low and moderate depth. I have seen evidence 

 of their work on shark catches made off Sovith 

 Carolina, Florida, Louisiana, Cuba, and southern 

 California. 



SUMMARY 



The overlapping geographical and habitat 

 ranges and superficial resemblance of Eulamia 

 milberti. the sandbar shark, and Carcharhinus 

 leu-cas^ the bull shark, have led to some confu- 

 sion and a tangled nomenclature. The recogni- 

 tion of milberti of Miiller and Henle as the spe- 

 cies name for the sandbar shark is based on the 

 opinion that pJvmbevs of Nardo is a vometi 

 nudem. 



The sandbar shark differs from the bull shark 

 in the structure and spacing of the dermal denti- 

 cles, in having a ridge in the skin of the back 

 between the first and second dorsal fins, and in 



