505 alewives was used for the analysis. Otoliths and 

 scales were read using a binocular dissecting scope 

 at 30x-60x. 



Each otolith and scale for an age shown in Figure 

 2 was collected from the same fish. The otoliths were 

 taken from the left side of the head and each scale 

 was chosen for the best annuli appearance of all 

 scales from that fish. The scale annuli shown are at 

 the anterior portion of the scale that is normally 

 covered by surrounding scales. The otoliths were 

 photographed with a 35 mm camera mounted on a 

 microscope at 11 x. 



Aging was done independently by two people 

 (readers; subsequently referred to as R^ and Rg). 

 Ages derived from scales and otoliths by each reader 

 were referred to as an age set. Scales and otoliths 

 were read without knowledge of fish length or sex. 

 A true age was established for each fish by reexamin- 

 ing scales and otoliths together with length and sex. 



The five age sets were compared to show 1) the preci- 

 sion of aging reproducibility (measurement of how 

 close the ages are for two or more readings); and 

 2) the aging accuracy (age determinations compared 

 with the true age). 



Three analyses were used to evaluate precision and 

 accuracy. Percent agreement (PA) compared two to 

 three age sets to reveal what portion of the fish were 

 aged alike between age sets. An index of average per- 

 cent error (APE) developed by Beamish and Four- 

 nier (1981) was used to show the degree of varia- 

 tion between age sets. APE is expressed as 



1 



N 

 I 



1 



R 

 I 



l^y 



X, 



where N is the number of fish aged; R is the number 

 of ways each is aged; X^ is the ith determination of 



3yr. 259mm (f 



4yr. 2 8 I mm (f 



5yr. 293mm <f 



Figure 2.— Gross comparisons of otoliths and scales of alewives from ages 3 through 7. The otolith and scale were taken from the 

 same fish for each age The age-3 otolith shows: A - anterior; P - posterior; D - dorsal; and V - ventral orientation of the otoliths 



698 



