20 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



them by chumming or by setting lines ahead of 

 them. The appearance of southbound schools at 

 Salerno was generally accepted as a harbinger of 

 better fishing a few days later. 



The southbound migratoiy movements of E. 

 milherti at Salerno were inshore and within the 

 southbound eddy of the Gulf Stream; north- 

 bound movements were not observed. It is sug- 

 gested that these movements were eitlier offshore 

 movements or slower movements of more diffuse 

 aggregations. Northbound movements offshore 

 would be aided by the Gulf Stream. An hypothe- 

 sis whicli may be more convenient than signifi- 

 cant is that E. milherti tends to follow currents 

 in migration and if the currents are strong does 

 not go against them. Of course, sharks would 

 not make appreciable headway against the cur- 

 rent at the surface near the axis of the Gulf 

 Stream without vigorous and persistent effort. 

 The sandbar shai'k does appear to take advantage 

 of eddies or countercurrents and the fishing 

 plans of some of the more successful shark fisher- 

 men were based on an assumption that the shark's 

 seasonal movements would follow tlie currents 

 available at the time. 



The distance traveled by various segments of 

 the population probably does not extend from one 

 end of the geographical range of the species to 

 the other. From the southern end of the nursery 

 range of the principal stock at Cape Canaveral, 

 a seasonal gradient of availability was shown by 

 catch per unit-of-effort data. This availability 

 decreased in summer southward and around the 

 tip of Florida to the west coast of Florida where 

 the species was completely absent from summer 

 catches. Thus, the minimum migratory travel of 

 the part of the stock reaching the vicinity of 

 Tampa would be approximately 600 miles. 

 Catches of E. milherti throughout the area be- 

 yond the southern end of the nursery range reach 

 their highest peak in midwinter. Catch per unit- 

 of-effort data previously published (Springer, 

 1951) show the catch of E. milberti at Salerno, 

 Florida, as decreasing from 4.8 fish per 100 hooks 

 for Februaiy to a low of 1.1 per 100 hooks for 

 September. A cold upwelling over the narrow 

 Continental Shelf immediately north of Jupiter 

 Light usually occurs in June or July. It is prob- 

 ably of brief duration but annually stuns great 

 quantities of fish, although the sharks are not 



affected. This phenomenon coincides with spec- 

 tacularly good shark fishing and possibly also 

 with considerable mating activity on the part of 

 E. milberti. This may give some bias to Salerno 

 catch per unit-of-effort figures for early summer. 



REPRODUCTION 



Courtship and mating 



I have seen neither the courtship nor mating of 

 Eulamia milherti. The general pattern may be 

 constructed, however, from fragments of infor- 

 mation and from inferences based on the few 

 facts known about related large sharks. The 

 comparative morphology of the secondary sexual 

 apparatus of male sharks has been given compre- 

 hensive discussion by Leigh-Sharpe in 11 papers. 

 The functions ascribed by Leigh-Sharpe in three 

 of these papers (1920, 1921, and 1924) to the vari- 

 ous parts of the ajjparatus in carcharhinid sharks 

 are in general accord with my observations on 

 GaUocerdo, the tiger shark. The courtship pat- 

 erns in Galeocerdo, Eula/mia milherti, and other 

 large carcharhinids probably do not differ 

 greatly. 



A brief outline of the mechanics of fertilization 

 in tlie carcharhinid sharks is included here to 

 oriept the reader in, following some of the infer- 

 ences made in later discussion of differential 

 death rates in the sexes. "^Carcharhinid sharks are 

 born alive and fertilization is internal. Paired 

 intromittent organs of the male known as clasp- 

 ers are supported by cartilages. Immediately 

 following the rapid enlargement of the testes, 

 which occurs at maturity, layers of calcification 

 appear at the surface on the principal clasper 

 cartilages. At this time the claspers become 

 semirigid except at the basal area of attachment 

 of the claspers to the base of the pelvic fin adja- 

 cent to the cloaca. The tip of each clasper, how- 

 ever, is expandible. When expanded, the carti- 

 lages of the tip are transverse to the main axis 

 of the clasper and open as the ribs of a fan. The 

 expanded tips are thought to serve both to liokl the 

 oviducts of the female open and to prevent with- 

 drawal of the claspers because of the rigid carti- 

 lages in a transverse position. The very large 

 clasper siplions are a distinguishing and peculiar 

 feature of the apparatus in male carcharhinids. 

 These siphons are a pair of separate sacs lying 

 just under the skin of the belly on either side of 



