Schueller et al.: Using a projector and microscope to read scales from Brevoortia tyrannus and B. patronus 
Table 3 
Results from tests of symmetry in ages estimated by examining scales on an 
Eberbach projector and a stereo microscope for Atlantic menhaden (Brevoortia 
tyrannus) and Gulf menhaden (B. patronus) sampled along the Atlantic and Gulf 
coasts of the United States. Scales were from Atlantic menhaden collected in 2013 
and 2017, Gulf menhaden collected in 2005 and 2017, and reference collections for 
each species. Reading 1 is the first reading of the sample set on both the projector 
and microscope, and reading 2 is the second reading on both instruments. Values 
are from comparisons of the 2 readings of scales in full samples and in subsam- 
ples on both devices and from comparisons of ages for subsamples determined 
on the same instrument. P-values for test results are provided in parentheses. 
n=sample size used for analysis. NA=not applicable. 
Data set 
Atlantic menhaden 
Reference 
Subsample: reading 1 
Subsample: reading 2 
Subsample: projector 
Subsample: microscope 
Gulf menhaden 
All 
2005 
2017 
Reference 
Subsample: reading 1 
Subsample: reading 2 
Subsample: projector 
Subsample: microscope 
but not for the other ages for both the Atlantic and Gulf 
menhaden (Fig. 3). The mean ages for samples taken in 
2017 and for samples from the reference collections were 
within the 95% confidence intervals for both species 
(Suppl. Figs. 16 and 17) (online only). However, the mean 
ages for older samples that were collected in 2005 and 
2013 were significantly different. 
Mean annuli distances for Atlantic and Gulf menhaden 
increased as counts of annuli increased (Suppl. Table 1) 
(online only). Scale distances measured at each annulus 
with a blue card were longer than those measured with the 
Eberbach projector and those measured with the micro- 
scope (Suppl. Fig. 18) (online only). Values were significantly 
different between the methods used, for the measurements 
from the focus to the second annulus and from the focus to 
the third annulus for Atlantic menhaden and for the mea- 
surement from the focus to the second annulus for Gulf 
menhaden (Suppl. Table 1) (online only). 
Readers 1 and 2 generally agreed on ages determined 
for samples from both reference collections (Suppl. Table 2) 
(online only), and APEs and ACVs were low for their age esti- 
mates. Average percent error was less than 5% for all com- 
parisons, except for the comparison of ages for the samples 
Bowker’s 
17.1 (<0.01) 
17.8 (<0.01) 
2.3 (0.51) 
1.0 (0.32) 
3.2 (0.68) 
16.8 (<0.01) 
10.3 (0.07) 
4.5 (0.60) 
73.7 (<0.01) 
74.4 (<0.01) 
4.4 (0.22) 
0.0 (1.00) 
19.8 (0.01) 
5.0 (0.08) 
11.5 (0.02) 
5.7 (0.13) 
Evans and 
Hoenig’s 
4.6 (0.10) 
2.8 (0.25) 
1.3 (0.25) 
1.0 (0.32) 
1.5 (0.48) 
16.2 (<0.01) 
9.9 (0.01) 
1.6 (0.44) 
69.8 (<0.01) 
72.1 (<0.01) 
3.3 (0.07) 
0.0 (1.00) 
12.6 (< 0.01) 
5.0 (0.03) 
6.0 (0.01) 
1.3 (0.25) 
McNemar’s 
3.9 (0.05) 
2.0 (0.15) 
1.3 (0.25) 
1.0 (0.32) 
0.2 (0.65) 
16.2 (<0.01) 
7.2 (0.01) 
1.5 (0.22) 
69.7 (<0.01) 
72.1 (<0.01) 
3.3 (0.07) 
NA (NA) 
12.5 (<0.01) 
5.0 (0.03) 
6.0 (0.01) 
1.3 (0.25) 
27 
of Gulf menhaden taken in 2005, for which the APE was 
12.0%. The PA for ages estimated for samples of Gulf men- 
haden taken in 2005, at 64.5%, was lower than the PAs for 
age data for the other samples, between 82.2% and 100.0%. 
Discussion 
Quality assurance (QA) and quality control (QC) are 
required for integrity of data collected or calculated as 
part of long-term monitoring programs and for the provi- 
sion of age estimates for fish sampled from commercial 
catches over a sequence of years (i.e., data from produc- 
tion aging) to be used in stock assessments. Quality 
assurance and QC are addressed differently in what is 
called research aging, which is geared toward a valida- 
tion method and typically uses smaller sample sizes 
within a shorter time interval in comparison with pro- 
duction aging (Morison et al., 1998). Because it spans 
long time periods and large numbers of samples, produc- 
tion aging requires QC to ensure consistency among 
readings of each reader and between readers and meth- 
ods for checking bias and minimizing errors to be 
