286 Memoir Sears Foundation for Marine Research 



feet, 6s to 70 pounds; 7 to 8 feet, 100 to 114 pounds; about 9 feet, 164 pounds." Al- 

 though we have handled many, we have weighed none. 



Developnental Stages. The Blue Shark is viviparous, its embryo having a well de- 

 veloped yolk-sac placenta attached to the uterine wall of the mother.*" The number of 

 young in a litter is large, 2 8 to 54 having been reported in the Mediterranean from females 

 of 8 feet 3 inches to 9 feet 4 inches." 



Habits. This is a pelagic species, encoimtered indifferently far out at sea and in con- 

 tinental waters, its wanderings no doubt directed chiefly by the search for food, although 

 it may drift with ocean currents. It is frequently seen at the surface, swimming lazily 

 with first dorsal fin and tip of caudal out of water, or basking in the sun. There is no 

 reason to suppose that it ever descends to any great depth. Many are seen in coastal waters 

 as well as offshore, and in some regions, near Woods Hole for example, it often comes 

 close enough to the land to be caught in pound nets, as many other sharks often are. 

 In our experience it is rather sluggish when not disturbed, but it swims powerfully and 

 swiftly when in pursuit of prey. Normally it feeds on the smaller fishes that may be 

 available locally, and on a variety of cephalopods. In northern waters herring and mack- 

 erel, and in European seas sardines, appear to be the chief items in its diet, as well as 

 Spiny Dogfish (Squalus acanthias). No doubt it also consumes large quantities of bottom 

 fish on the fishing banks. For example, we have repeatedly had Blue Sharks pick up cod, 

 haddock and American pollock (Pollachius virens) that had b?en returned to the water 

 on Georges Bank during the cod-tagging cruises of the United States Bureau of Fisheries. 



In warmer seas they are also known to feed on anchovies and flyingfish, and occa- 

 sionally on a sea bird that is resting on the water. We find no record of their preying on 

 larger animals while the latter are alive. They sometimes follow sailing vessels in warm 

 seas for days or even weeks picking up offal. And their habit of gathering when a Sperm 

 Whale has been killed, probably by tracing the blood-scent, has long been proverbial 

 among whalemen, one often struggling up on the carcass to "cling there until a descending 

 blubber-spade had put an end to all its ambitions," to quote from an eye-witness account. 

 "If the cutting in of the whale was at any time deferred . . . the sharks . . . would then 

 attack the carcass, and, thrusting their heads partly above the surface, would bite large 

 mouthfuls out of the blubber. ... A blue shark horribly mutilated by repeated thrusts 

 of a whaleman's blubber-spade, was seen to return immediately to the whale on which it 

 had been feeding and to continue ravenously. . . . "" A recent report of one that came to 

 eat scraps thrown to it from a boat, even after it had been transfixed by a harpoon, similarly 

 illustrates its indifference to injury.** 



14. From Roule, Result. Camp. sci. Monaco, 52, 1919: 1145 Holcombe, Modern Sea Angling, 1921: 144; Sdiultz 

 (J. Mammal., ip, 1938: 484, "Prionace") gives a weight of 433.6 kg. (about 950 pounds), but this is so far 

 out of line with other recorded weights that some other stouter-bodied shark was doubtless intended. 



15. For a recent anatomical account of the placenta, with references, see Calzoni (Pubbl. Staz. zool. Napoli, 75, 

 1936: 109). 



16. For numbers and sizes of embryos, see Lo Bianco (Mitt. zool. Sta. Neapel, 19, 1909: 666). 



17. Nichols and Murphy, Brooklyn Mus. Sd. Bull., 5 (1), 1916: 11. 



18. Piers, Proc. N. S. Inst. Sci., 18, 1934: 202. 



