NATURAL HISTORY OF THE SANDBAR SHARK 



25 



thAtl\ milbn-ti Ai birtl 



reasonable to expect that E. mUbrrti at biith may 

 be somewliat smaller in the northern part of its 

 rang:e than in the southern part and that the 

 •rrowth rate in cooler waters is slower. 



Abnormal embryos ^^^- ,,] \ 



In the lute spring of r,>42 {^collected at Salerno. 

 Fla., a series of ^uVirhia inilherti embryos of 

 both sexes and near full term which were ap- 

 parently perfect except for having the eyes on 

 the lower side of the snout, almost in contact 

 with one another and just posterior to the nos- 

 trils, and having no trace of an opening in the 

 skin for the mouth, although the jaw cartilages 

 were apparently normal. 'Pfie specimens were 

 pregwivfitLi n form alHF%Trt dried put during the 

 following years and were discjlfded. Again in 

 I J9*46 similar embryos were collected, and a^out 

 / half fi ibafrel were preserved; but all were lost in 

 * a -Wfrtlcane whidi destroyed^ a dock building. 

 ^ No ab« ormal yoonfr-Were found m the rela- 

 tively Irffge series of litt«irs.£iamined^in 104$ and 

 J had iio later ojjportunity to see substantial 

  mimbers of E. milherti embryos. All litter mates 

 exlillmed the same abnormal condition and were 

 remarkably uniform structurallj\ A very rough 

 estimate of the frequency of occurrence is one set 

 of abnormal young in .500 to 1.000 sets of ap- 

 parentl)' normal pups. 



SEX RATIOS ^^ 



It was the general observation that landings 

 of adult Eulamia miJherti at Salerno were in the 

 ratio of 5 females to 1 male. A similar sex ratio 

 was estimated for Salerno landings of E. ohscwa 

 and for Bahama landings of ^^v'K.^spviMj'Ti. 

 A disproportionately large numter of female E. 

 ilorid(Mut were landed at Sa>rno but the records 

 do nqt furnish an adequate basis fop'an estiipiue. 

 An insufficient number of E. alfiina or E. npring- 

 eri were recorded for estimate. Murphy and 

 Nichols (1916) say that the commonest large 

 sharks in the waters about New York are the 

 gromid sharks (Carcharhmm), and also that 

 males of tliese fishes are rarely .seen but toward 

 midsummer many of the females enter our bays 

 where they give birth to their young. They 

 further stii,te that the cojinnonest ground shark 

 is Carcharhinus ntilbertii The only record sug- 

 gesting etjuality in the number of adults of the 

 sexes of E. milbet'tl is Captain Winkler's record 



of the captuie of 26 males and 2.5 females off the 

 Caribbean coasts of Nicaragua and Costa Rica 

 in the fall. ' / / 



Data on the sex ratio in young E. milherti is 

 limited to a series of 203 young from 26 to 50 

 inches long collected by otter trawl in Februaiy 

 1958 off/N"oith (>rolin!v. Tli/re vy^re Ol^^tiales 

 and It^ fejuliles'in thii? collection. 



Florida shark fishery records of carcharhinids 

 otlier than those of the genus Eulamia show local 

 segregation by .sex and size but in no other car- 

 charhinid nor in the hammerheads is there any 

 clear indication ft^onr'availa^e _r©eords from 

 Florida of/greivt imbalance m the sex ratios of 

 adults, y' 



Tilt unavailability of male milherti to baited 

 hooks during the mating season maA' explain in 

 ])art the smaller number of males in the landings. 

 However, beca/use Florida commercial shark fish- 

 ing after 1946 was carried on out to depths 

 greater than the maximum known depth range of 

 the fspecies, and because the males brought the 

 fishermen a higher price than the females, it is 

 certain that there was no intentional selection of 

 females^^Tlie fishermen believed that the schools 

 of males, if found, were easier to catch in large 

 nunibers.- Females were far more abundant than 

 males in the deeper water catches made off the 

 Florida Keys in the late fall and early spring, 

 and a much greater abundance of females char- 

 acterized the winter catches on the west coast 

 of Florida. 



It has already been shown that approxinuitely 

 equal numbers of male and female milherti are 

 born. The evidence that there are substantially 

 more females than males in the adult ]in]iulation 

 is very strong, if sui' information adecjuately 

 covers the geographical range of the species. Al- 

 though if is quite possible that segments of the 

 adult population have been entirely overlooked 

 in the offshore and midwater depths in the north- 

 ern jiart of its range, the shortage of males in the 

 population around .southeiii Florida is remark- 

 able. 



There is some indirect evidence also of a short- 

 age of males in the breeding population. If the 

 females bear pups in alternate years. .50 percent 

 of the adult females wduld be expected to be 

 gravid in winter. I have previously reported 

 (Springer, 194(» ^uit tmly, ;i^qut ,1J pe^ceut ufjhe 



