12 



FISHERY BULLETIN OF THE FISH AND "WILDLIFE SERVICE 



any other gear. Each unit of gear consisted of a 

 main line of chain or wire rope a half-mile or 

 more in length. This was set on the bottom, 

 anchored at both ends with the anchors rigged 

 with buoys so that the lines could be retrieved. 

 Short, branch lines made of chain, each with a 

 baited hook, were spaced at intervals of 20 to 40 

 feet along the central part of the main line. The 

 typical unit, had 100 hooks. Flof^ting lines and 

 anchored gill net's wer^'alao, -tt^d-eScasibnally 

 in the fishery. 



Positive information from the shark fishery on 

 the distribution of E. milherti is quite volumi- 

 nous and detailed. Systems of payments to fish- 

 ermen required detailed records involving iden- 

 tification and measurement of all sharks landed 

 by ves.sels of the principal fishing company. Al- 

 together, records of landings of more than 

 100,000 milberti during a period of 15 years have 

 been examined. 



Information on the absence of E. milberti from 

 si>ecific areas has been difficult to assemble, but 

 here also the records of the shark fishery supply 

 most of the data. The species was firet repoi'ted 

 in the Florida area from correctly identified 

 specimens after the commercial shark fishery 

 began (Springer, 1938), so the earlier scientific 

 literature has been useless in the establish- 

 ment of the range of the species in the Florida 

 area southward. Offsliore records, from areas 

 where water depths are more than 500 fathoms, 

 are exclusively from catches made on tuna 

 longlines used by the exploratory fishing vessel 

 Oregon (for descriptions of this gear see 

 Bullis, 1955, and Captiva, 1955). Some infonna- 

 tion on the distribution of the young was obtained 

 from otter-trawl catches made by the exploratory 

 fishing vessel Delaware off the coast of North 

 Carolina. Additional scattered records were 

 picked up from accidental catches made by com- 

 mercial and sport fishermen who used various 

 types of gear, from catches made by collectors 

 fishing for aquarium specimens, and from biolo- 

 gists who captured specimens incidental to other 

 collecting activities. 



The area of greatest uncertainty is in the off- 

 shore and midwater range. Recent marine ex- 

 ploration has shown that substantial populations 

 of large sharks, fishes, and invertebrates live in 

 subsurface waters beyond the Continental Shelf 



where they have escaped the attention of natu- 

 ralists. On June 11, 1954, the first E. milberti 

 known from waters beyond the Continental Shelf 

 was taken on a tuna longline hook at USFWS 

 Oregon station 1099, 85 miles off the coast of 

 Texas where the depth was approximately 600 

 fathoms. Since the hook was set to fish at about 

 30 fathoms, this shark, an adult male, was cruis- 

 ing in midwater. Throughout the second half of 

 1954, all of 1955, and the first part of 1956, long- 

 line fishing was carried on in the offshore waters 

 of the Gulf of Mexico by the M/V Oregon and a 

 few commercial vessels. Large numbers of sharks 

 were taken, chiefly species known to be partly or 

 entirely pelagic. No additional milberti were 

 taken until early February 1955, when a com- 

 mercial vessel caught two adult females about 50 

 miles off the northern edge of the Campeche 

 Bank where depths were estimated to be more 

 than 1,000 fathoms. These sharks were caught 

 on longlines with hooks fishing not more than 

 50 fathoms deep. These three captures, outside 

 the principal range, appear to have little signifi- 

 cance in the general picture of the distribution 

 of Eula7nia milherti. 

 Factors affecting distribution 



It may be assumed that water temperature and 

 salinity are important in limiting the distribution 

 of the sandbar shark and that there are other 

 factors clearly influencing the movements and 

 distribution of the species. The reaction of sand- 

 bar sharks to ocean currents, the availability of 

 food, the relation between the growth rate or the 

 reproductive pattern and the migratory move- 

 ments, all appear to be important in forcing the 

 species into a particular range. No data are 

 available, however, to show the relative strengths 

 of these conditions as determinants of the range 

 of the sandbar shark. 



The facts, from superficial examination at least, 

 do not support the thesis that competition with 

 other species is a powerful influence in the selec- 

 tion of a particular range. Young Eulamia mil- 

 berti, for example, apparently caiuiot long sur- 

 vive where large Carcharhimis lencas in propor- 

 tion to milberti are relatively abimdant. The 

 presence of large numbers of large C. levcas in 

 the vicinity of the nioiitli of the Mississippi River 

 seemingly does not deter gravid female milberti 

 from moving into the area to give birth to young. 



