NATURAL HISTORY OF THE SANDBAR SHARK 



21 



the midline and extendinjr from the pelvic to the 

 pectoral ureas. They function as reservoirs for 

 the sea water used to flush the male sex cells from 

 the bases of the claspers into the oviducts of the 

 female during mating. The siphons may hold a 

 large amount of sea water, as much as 2 gallons 

 in Guleottrdo. The siphons do not ordinarily 

 contain the sea water which is presumed to enter 

 the siphons during the period immediately pre- 

 ceding mating. 



During the mating season the area at the bases 

 of the claspers of the larger carcharhinids exhibit 

 extraordinary vascular congestion. Characteris- 

 tically, in male Galeocerdo, a mass of very soft 

 spongy tissue appears around the cloaca. This is 

 present to a lesser degree in the smaller carchar- 

 hinids such as t!^ milberti. Unusual congestion, 

 edema, and suboermal hemorrhage at the base of 

 the claspers are evidences of courtship activity on 

 the part of the male. 



Large sharks are not highly maneuverable and 

 cannot swim backward, so it is necessary for the 

 claspers to rotate and point forward during mat- 

 ing. Since the muscle system in the typical 

 carcharhinid clasper seemed functionally inade- 

 quate or feeblf, I carried out an experiment 

 which incidentally revealed the probable method 

 by which the clasper siphons are filled with sea 

 water. I oTitained an adult male Carcharhinus 

 lirnhatus about 5 feet long and evidently in mat- 

 ing condition. The choice of species was dic- 

 tated by circumstances, one of which was the fact 

 that a 5-foot shark was as large as I could man- 

 aged By injecting a considerable quantity of an 

 isotonic solution into the caudal vein, ^'^as able 

 to induce the claspers to assume the normal mat- 

 ing position. This action caused the claspers to 

 revolve inward and forwai-d. As the claspers 

 moved into a forward pointing position, a funnel, 

 formed by a membrane supported by rods of 

 cartilage, opened at the base of each clasper. The 

 mouth of the funnel was also directed forward 

 and the constricted end led into the siphon. The 

 caudal vein was plugged experimentally to hold 

 the claspers and funnel in position and the shark 

 was moved forward as rapidly as possible 

 through tlie water. This caused the clasper 

 siphons to fill with water. Application of addi- 

 tional pressure to the caudal vein resulted in com- 

 plete expansion of the fanlike tip of each clasper. 



The course of courtship and mating in all of 

 the larger carcharhinids including Ey milberti 

 probably follows the pattern in which the male 

 persistently follows and occasionally bites the 

 female on the back until she swims upside down. 

 Both claspers probably function at the same time, 

 one entering each oviduct of the female by way 

 of the lateral opening from the cloaca. The con- 

 tact of the two sharks may be presumed to force 

 the sperm-ladened sea water from the siphons 

 into the oviducts. 



The mating pattern has been given in .some de- 

 tail to emphasize the point that mating is very 

 complicated in carcharhinids, and that the me- 

 chanical difficulties are compounded among the 

 larger species by their greater weight and lesser 

 maneuverability. 



Time of mating 



The approximate period of the mating season 

 is established by the appearance of males with 

 enlarged testes and also with some evidence of 

 vascular congestion of the pelvic-fin area and by 

 the appearance of females with eggs of full size 

 in the ovaries (about 1 to li^ inches in diameter 

 in l^mllberti) . In the vicinity of Salerno, Fla., 

 mating of ^milberti evidently takes place in the 

 spring or early summer. Males appear commonly 

 in inshore catches after the firet of Februaiy but 

 remain segregated for some time. Catches of 

 both sexes indicating mixed schools are more fre- 

 quently made in April and May than in other 

 months. After Ma}\ male i^. milberti are rela- 

 tivel}' scarce in Salerno catches. Among car- 

 charhinids, the males may stop eating during the 

 courtship period. This is an inference drawn 

 partly from the general reduction of catches of 

 males on baited hooks during mating seasons, 

 partly from the observed smaller size of the 

 livers of males immediately following the mating 

 season, and partly fiom observations on the mat- 

 ing activity of Galeocerdo. 



Fertilized eggs and the smallest detectable em- 

 bryos were observed first in Salerno catches from 

 the first part of July to the first ]>art of August. 

 Tlu' time of mating can be established with more 

 l)recision, however, by observation of the time of 

 appearance of the fresh courtship scars on the 

 females. Scars, tooth marks, and ismall open 

 wounds produced by shark teeth are conunonly 



