Figure 2.— Scale from 5-year-old American shad. FWZ marks the fresh-water zone. 1, II, and III 

 represent annular rings. SM represents a "spawning mark" which also Is an annular ring. 



Scales can also be used to tell how many- 

 times a shad has spawned. A shad does not 

 feed during the spawning run, so the edge 

 of the scale becomes resorbed by the fish. 

 This resorption causes a scar or "spawning 

 mark" on the edge of the scale and occurs 

 about the same time a new annulus forms; 

 thus the "spawning mark" is also counted 

 as an annulus or year mark. 



Rate of Growth 



American shad grow fast during their first 



3 years of life. Average lengths are 5 to 6 

 inches at 1 year, 9 to 10 inches at 2 years, 

 and 10 to 14 inches at 3 years. After the 

 first 3 years, the growth rate decreases. 

 The average length is 15 to l6 inches at 



4 years of age and 1 8 to 19 inches at 5 years. 



Migrations 



American shad, like salmon, migrate thou- 

 sands of miles in the ocean and then return 

 to spawn in the stream in which they were 

 hatched- - how they are guided is still a mystery. 

 On the Atlantic Coast, adult shad that survive 

 after spawning migrate back to sea and north- 

 ward to the Gulf of Maine, where they spend 

 the summer and fall feeding on abundant 

 plankton. Scientists believe they winter in 

 deep water off the Middle and South Atlantic 

 States. As spawning season approaches, mature 

 fish migrate inshore and move either south- 

 ward or northward to their natal streams 

 to spawn (fig. 3). They repeat this cycle each 

 spring. Young shad leave the rivers in fall 

 and probably overwinter in the ocean off the 

 Atlantic States. In summer they presumably 

 migrate with the adults to the Gulf of Maine. 



