32 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



that E. milhcvrti does not live to a great age and 

 tliat those individuals migrating a great distance 

 to the coast of Nicaragiia-Costa Rica do not re- 

 turn. . 



ABUNDANCE 



Tlie insliore range of tlie sandbar shark has 

 made this species readily available to tlie shark 

 fishery. This was particularly noticeable at Sa- 

 lerno, where the range is restricted by a narrow- 

 ing of the Continental Shelf and where special 

 conditions of current and temperature tend to 

 jiroduce a narrow path inshore for the south- 

 bound migrants. Approximately 58 percent of 

 the sliarks landed by the fishery at Salerno be- 

 tween 1938 and 1946 were sandbar sharks. Al- 

 tliough present throughout the year, they were 

 comjiaratively more frequent in Salerno catches 

 from December through July as shown by rec- 

 ords of the catch jier unit of effort (Springer, 

 .19.51). Except for winter fishing on the south- 

 west coast of Florida whicli produced a few 

 hundred E. milherti each winter, few sandbar 

 sharks were taken in the Gulf of Mexico. 



It is estimated that during the period 1935 to 

 1950 from 5,000 to 15,000 sandbar sharks were 

 taken yearly fi-om the entire range of the fishery 

 and that these were nearly all adults with an 

 average weight of about 130 pounds. The yearly 

 catch might be estimated, therefore, as between 

 650,000 and 1,950,000 pounds, a small quantity 

 compared with yearly landings by the commer- 

 cial fishery of many species of bony fishes. Dur- 

 ing the years that the shark fishery operated, it 

 was prosecuted vigorously, and. although there 

 was no evidence that fishing pressure reduced tlie 

 stock of sandbar sharks, it was found that the 

 catch per unit of effort was reduced by concen- 

 trating too much gear in one area. Efforts to 

 expand production were successful chiefly by ex- 

 tension of the area of fishing into the ranges of 

 other species of sharks. A fluctuation in abimd- 

 ance with a low in every third year was found in 

 the catch per unit of effort at Salerno (Springer, 

 1951). _  



Although data are lacking to support such a 

 contention except observations at sea, it is esti- 

 mated that several other species of Eulamia. par- 

 ticularly E. -floridana. occur in substantially 

 greater species-mass around Florida than does E. 



milherti, chiefly because of the greater area of 

 their habitats. 



It is generally recognized that marine animal 

 populations are unstable and are subject to re- 

 markable changes in total numbers and occasional 

 shifts in geographical range. Such changes may, 

 of course, occur in the Atlantic population of 

 E. mUberti. 



A concentration of E. milberti appeared for a 

 few days in the late spring or early summer of 

 1935 off Dog Keys Pass on the coast of Missis- 

 sippi. These sharks were not only out of their 

 normal range but behaved in a way that is not 

 normal for milherti or perhaps for any shark. 

 They struck at anything thrown into the water, 

 fought one another over pieces of charcoal, fought 

 so vigorously that some were killed and eaten 

 by others of the school. Sharks frequently fol- 

 low shrimp boats such as we were using at the 

 time, and churn tlie surface of the water after 

 scrap fish thrown overboard; but the intensity 

 of this attack by out-of-range milherti was much 

 stronger than any shark action I have seen since. 



Although no great fluctuations were noted in 

 the general abundance of E. milherti during the 

 period from 1935 to 1950, its competitor, the bull 

 shark C. levcas. appeared once to go through a 

 major but temporary shift in abundance. In 

 1937 so many bull .sharks were caught off Salerno 

 that catches exceeded the demand. The company 

 buying siiark livers and oil was forced to delay 

 payments to fishermen for a period of several 

 months. This was not merely a matter of eco- 

 nomic adjustment to be settled by a reduction in 

 price but the supply of tanks and drums for 

 storage of liver oil was exhausted and a court 

 injunction was finally issued to stop all shark 

 landings because shark carcasses were accumulat- 

 ing along the shores. This was the 6nly known 

 a]ipearauce of bull sharks in large numbers on 

 the east coast of Florida. It seems likely that 

 persistence of great numbers of bull sharks, es- 

 pecially north of Cape Canaveral, would have 

 adversely affected tlie |)opidation of E. milherti. 



ENEMIES 



The principal predators on sharks are other 

 sharks of larger size. Wherever concentrations 

 of mixed sizes occur predation by the lai'ger 

 sharks on the smaller ones is normal. The con- 



