AGE DETERMINATION OF AMERICAN SHAD 



167 



Figure 6. — Scale from "j-year-old marked shad spawning for the second time. 



fish spawning for the first and third times.^ Those 

 spawning for the third time had first spawned in 

 1956 when 4 years old. The second spawning 

 mark was laid down in 1957. Marked males 

 averaged 18.2 inches fork length and 3.6 pounds 

 in weight. Marked females averaged 19.1 inches 

 fork length and 4.5 pounds in weight. 



DISCUSSION AND CONCLUSION 



Of the 1'29 fish classified from radiographs as 

 marked, only 3 were in disagreement with age as 

 determined from scale readings. These misclassi- 

 fications, 2 in 1957 and 1 in 1958, were caused by 

 error either in age determination or in inteq)reta- 

 tion of radiographs, which in some cases were 

 difficult to interpret. This minor disagi-eement, 

 approximately 2 percent of the fisii classified as 



' Fipure 1 is n represptitative scale from a 6-.vear-oId marked 

 shad spawninc fur tlic second time. These flsh had first spawned 

 In 1957 when 5 years old. 



marked, was considered insignificant and in no 

 way invalidates the findings of this report. 



Methods used by Ivcim (192-1), Borodin (1925), 

 Greeley (1937), and Gating (1953), to age shad 

 were all considered in this study. Of these 

 methods, only Gating's proved to be a complete 

 and valid means for determining total age, age at 

 first spawning, and number of times previously 

 spawned. LaPointe (1958) correctly validated 

 the annulus as a true year mark on scales of shad 

 spawning for the fii-st time and he showed that 

 I^im had mistaken the fresh-water mark for the 

 first aitnulus. Therefore, the techniques used by 

 I^eim and Greeley to age shad gave age assessment 

 1 year greater than the actual age of the fish. 

 Borodin's method, applied to scales of marked 

 shad, gave eiToneous results and could not be justi- 

 fied on the basis of the present study. 



Age of marked fish collected in 1950, 1957, and 

 1958 as determined from scale readings, was in 



