National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
e established in 1881 «<< 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Abstract—Age determination is import- 
ant for estimating productivity and 
status in fisheries stock assessments. 
Aging methods must balance advances 
in technology with continuity of data 
for long-term sampling programs. 
The long-term sampling program for 
Atlantic menhaden (Brevoortia tyran- 
nus) and Gulf menhaden (B. patronus) 
has resulted in a database of ages that 
were determined by using an Eberbach 
projector, a now outdated technology. 
The objective of this study was to com- 
pare ages determined with an Eberbach 
projector to those determined with 
a more recent technology, the ste- 
reo microscope. Scales from Atlantic 
(total number of fish [N]=1317) and 
Gulf menhaden (N=1569) were aged 
by using both an Eberbach projector 
and a stereo microscope, and results 
were compared by using percent agree- 
ment, average percent error, Chang’s 
average coefficient of variation, bias 
tests, and simultaneous multinomial 
confidence intervals. The results from 
these measures for comparing age esti- 
mates were generally within standard, 
expected levels. Some bias was detected 
between estimates from the use of the 2 
devices but was likely due to the use of 
poorly preserved scales or images of low 
quality on the Eberbach projector. Our 
results indicate that the use of a micro- 
scope will help maintain continuity in 
age estimates over time for long-term 
monitoring and for stock assessments. 
Manuscript submitted 2 July 2020. 
Manuscript accepted 8 March 2021. 
Fish. Bull. 119:21—-32 (2021). 
Online publication date: 5 April 2021. 
doi: 10.7755/FB.119.1.4 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Comparison of ages determined by using an 
Eberbach projector and a microscope to read scales 
from Atlantic menhaden (Brevoortia tyrannus) 
and Gulf menhaden (B. patronus) 
Amy M. Schueller (contact author) 
Amanda Rezek 
Raymond M. Mroch Ill 
Eric Fitzpatrick 
Alicia Cheripka 
Email address for contact author: amy.schueller@noaa.gov 
Beaufort Laboratory 
Southeast Fisheries Science Center 
National Marine Fisheries Service 
101 Pivers Island Road 
Beaufort, North Carolina 28516 
Determining the health of fish popu- 
lations is of the utmost importance to 
ensure that fishery yields are sustain- 
able over time. Knowledge of the life 
histories of species is integral to under- 
standing the population dynamics and 
factors that may influence the sustain- 
ability of a fishery. Several life history 
statistics, including size estimates for 
fishable year classes, can be determined 
by knowing the age of individuals caught 
(June and Roithmayr, 1960; Campana, 
2001). Collecting these age data can be 
done by grouping fish by length frequen- 
cies or by counting annuli on otoliths 
or scales (Secor et al., 1995; Campana 
and Thorrold, 2001). Determining age 
through the use of otoliths can some- 
times be impractical because of the time 
and effort required to extract, prepare, 
and age the structure. The use of scale 
samples can yield age data, and the col- 
lection and preparation time required is 
significantly less for using scales than 
for using otoliths (Nicholson and Schaaf, 
1978; VanderKooy'). Aging with scales 
 VanderKooy, S. (ed.). 2009. Gulf menhaden 
Brevoortia patronus. In A practical hand- 
book for determining the ages of Gulf of 
also does not require sacrificing the fish 
(Khan and Khan, 2009; Vilizzi, 2018). 
Age data from collected scales and 
otoliths are used to calculate statis- 
tics such as productivity of a popula- 
tion, growth rate, and mortality rate 
(June and Roithmayr, 1960; Campana, 
2001). These calculated variables form 
the basis of stock assessments, which 
provide information essential to the 
management of fisheries. Specifically, 
age data include catch composition 
and the age classes represented by 
survey data and can be used to track 
cohorts through the population over 
time and to estimate life history char- 
acteristics, such as growth rate, natu- 
ral mortality, and fecundity (Beamish 
and McFarlane, 1995; Morison et al., 
1998). All of these data are used to 
estimate parameters in stock assess- 
ments; therefore, the process of aging 
fish is critically important. 
Atlantic menhaden (Brevoortia tyran- 
nus) and Gulf menhaden (B. patronus) 
Mexico fishes, 2nd ed., p. 5-70-5-73. Gulf 
States Mar. Fish. Comm., Publ. 167. Gulf 
States Mar. Fish. Comm., Ocean Springs, 
MS. [Available from website.] 
