184 Memoir Sears Foundation for Marine Research 



dorsal, with broadly rounded corners. Pectoral about % as broad as long, with broad base, 

 its outer and inner margins moderately convex, its distal margin nearly straight or very 

 slightly concave, its corners broadly rounded} about lYo times as large in area in males as 

 in females. 



Color. Rich yellowish to grayish-brown, darker above than below. Small specimens 

 are usually sparsely and variously marked with small dark spots below as well as above, 

 sometimes with brown crossbars across the snout and through the dorsals, ventrals and 

 analj adults may or may not retain these markings; also, some young specimens are plain- 

 colored. 



Size. The Nurse Shark is small at birth, free-living specimens of only 270 to 290 

 mm.' being recorded, but it grows to a very considerable size, specimens of 7 to lO or 1 1 

 feet being commonly reported, with 11 to 12 feet not unusual. The maximum so far re- 

 ported is about 14 feet, but maturity may be attained at a comparatively small size, as in the 

 case of a female of only 5 feet that contained well developed embryos.* The weight is 

 given as about 330 to 370 pounds at about 8 V2 feet; 4V4 pounds at 2 feet 3V2 inches (692 

 mm.). 



Develo-pmental Stages. Both ovaries may be functional,' or only one, with the other 

 atrophied. Mature eggs are very large (reported up to 130 X 180 mm.), blunt-ended, 

 with brownish-black, thin, horny shells. They remain in the hinder parts of the oviducts 

 until the shells break and the young are hatched into the uterus.'" 



Later in development embryos have a short umbilical cord, with very large sub- 

 spherical or oval yolk sacs; the external gill filaments are retained up to a length of 130 

 to 140 mm. The length of the nasal barbel and the size of the eye decrease from embryo 

 to adult, but the fins increase in relative size. Females have been described as containing as 

 many as 28 large eggs; a West African specimen (2.43 meters long) has been reported as 

 giving birth to 26 young on capture." 



Habits. In its centers of abundance, from Florida to the Caribbean region, this Shark 

 appears chiefly inshore, often in water as shallow as two to ten feet. It is frequently en- 

 countered in channels between the mangrove keys. Schools of one to three dozen are some- 

 times seen on sand flats and over rocky bottom where they are easily approached, the 

 sharks often lying motionless and close to one another, with dorsal fins out of water. Pro- 

 verbially sluggish in habit, the "Nurse" feeds chiefly on invertebrates — squids, shrimps, 

 crabs, spiny lobsters {Palinurus), sea urchins — and small fish. They bite readily on 

 almost any bait. It is common knowledge that they come into very shallow water to breed, 

 and here they are often seen mating. While in the act of copulation the male grasps the 



7. See Study Material, p. iSi; also Beebe and Tee-Van, Zoologica, N. Y., lo, 19:8: 26. 



8. Beebe, Zoologica, N. Y., 26, 1941 : 9. 9. Bell and Nichols, Copeia, 92, 1921 : 17. 



10. For an account of eggs and early development, see Gudger (Yearb. Carnegie Instn., 1912: 11, 149; Copeia, 98, 

 1921: 57). 



11. Budker (Bull. Mus. Hist. nat. Paris, [2] 7, 1935: 183) substantiates the general report that the number of 

 young in a litter is large. 



