FISHES OF THE GULF OF MAINE 



113 



is much warmer — -70° to 75° instead of 55° to 60°.^^ No exact information as to 

 the time of spawning in northern New Enghxnd rivers is available. About Woods 

 Hole this takes place in early summer in small ponds with an outlet to salt water, 

 most of the females being spent, a few females and many males ripe, and others of 

 both sexes still unripe in July. The eggs are about 1 mm. in diameter, sink like 

 those of the alewife, and are adhesive. Incubation occupies only about 50 hours at 

 a temperature of 72°, the newly hatched larvae averaging 3.5 mm. in length but 

 growing ^vithin 24 hours after hatching to 4 mm., with the greater part of the yolk 

 sac already absorbed. Within a month they are 30 to 50 mm. long, and already 

 show most of the diagnostic characters of the adult. Evidently the young soon 

 find their way down to the sea, for bluebacks of 50 mm. have been seined in abun- 

 dance in Rhode Island waters late in July. Notliing whatever is known of their 

 rate of growth there. The spent fish, like alewives, return to sea shortly after 

 spawning. Probably these are the bluebacks taken at Woods Hole and north of 

 Cape Cod in September and October. The winter home of our bluebacks is 



~yyii 



'*"*^, 



ITi. 



^^^^7 





Fig. 46.^AduIt shad {Aiasa sapidissima) 



unknown; probably, like their relative the sea herring, they move out from land 

 and pass the cold season near the bottom. 



We need only note further that the blueback is as gregarious as the herring or 

 alewife; that it is equally a plankton feeder, subsisting chiefly on copepods and 

 pelagic shrimp, as well as on young launce and, no doubt, on other small fish fry. 

 In commercial use no distinction is made on our coast between the blueback and 

 the more abundant alewife — it is equally useful for bait and human food. 



43. Shad (Alosa sapidissima Wilson) 

 Jordan and Evermann, 1896-1900, p. 4'27. 



Description. — ^The shad resembles the alewife in the fact that its body is much 

 deeper than thick and that its belly is sharp edged with bony serrations. In all 

 respects it is a typical herring, with soft rayed dorsal and anal fins of moderate size, 

 the former situated above the ventrals and weU forward of the middle of the bodv. 



" The early development and larval stages of the blueback are described by Euntz and Radclifle (1918, pp. 87-134) . 



