Elzey et al: Comparison of 4 aging structures for Alosa sapidissima 
49 
were captured during the time of presumed annulus 
formation, the edge of each structure was counted as 
the final annulus. 
Only fish for which all 4 structures were deemed 
readable were included in this study. Each structure 
was read independently by 2 readers with no knowl- 
edge of fish size, sex, or ages assigned to other struc- 
tures. Readers used scales, otoliths, opercula, and ver- 
tebrae from fish not included in the study to familiarize 
themselves thoroughly with each type of structure be- 
fore beginning the final reading. Precision of readings 
was measured with percent agreement and coefficient 
of variation (CV) (Chang, 1982) 1) between results for 
one reader and results for the other reader for each 
structure, 2) among results for reader 2 for a randomly 
assigned subsample of 100 fish, and 3) between results 
for otoliths and results for each of the other 3 struc- 
tures for each reader. Coefficients of variations were 
calculated with the equation as shown in Campana 
( 2001 ): 
\ 2^( = l D 1 
This equation gives the CV for the j th fish, 
where X tJ - the ith age estimate of the j th fish; 
X, = the average age estimate of the j th fish; and 
R = the number of times that fish was aged. 
Coefficients of variations listed in this article were av- 
eraged across all fish aged. Wilcoxon rank sum tests 
were used to determine whether differences in age 
readings existed between otoliths and the other struc- 
tures. Significance was not tested for fish of ages 3 and 
11 because of insufficient sample sizes. 
Figure 1 
Images of an (A) otolith, (B) vertebra, (C) scale, and (D) operculum from a 5-year-old male American shad ( Alosa sapidis- 
sima) that was captured on 31 May 2010 in the Merrimack River in Lawrence, Massachusetts. The dots on each image 
indicate locations of presumed annuli. This fish was captured during the spawning season, which is also the period of an- 
nulus deposition; therefore, the edge is counted as the fifth annulus. 
