AGE OF ATLANTIC SHAD FROM SCALES 



189 



Fk, i re 2. — Scale from a 4-.vcar-<>ui male sh.nl [iifjisnrinj; Hi.- inches and weighing 2 pounds 8 ounces 



when young shad pass from fresh to salt water at 

 the end of the first summer. Some workers ap- 

 parently have called this the iirst winter annulus, 

 but Hammer (1942) has shown that this line 

 forms at the time of transition from fresh water 

 in the parent river to salt water in the ocean when 

 the shad are from :'> to •"> months old. Figure 3 il- 

 lustrates the scale of a young Hudson River shad 

 estimated to be 4 or ."> months of age and nearly 

 ready to leave fresh water for salt water. If this 

 shad had lived longer the scale, as seen now. would 

 have formed the fresh-water zone of the larger 

 scale. 



1. Spawning marks. — These marks are scarlike 

 rings extending- around the anterior portion of the 

 scale much as do the annuli, but unlike the annuli 

 they extend only a short distance into the poste- 

 rior portion of the scale. These marks are caused 

 l>y absorption, or erosion, of the scale during the 

 spawning migration into fresh water where little 

 or no food is eaten by the adult shad. Figure 4 

 shows the condition of the edge of a scale from a 

 shad just entering the Hudson River on the spawn- 

 ing migration. Notice the smooth margin. Fig- 

 ure  > illustrate- the irregular margin of a scale 

 taken from a shad well up the river on the spawn- 



