22 
Fishery Bulletin 119(1) 
are 2 commercially important species in the United States 
for which the stocks are routinely assessed (SEDAR, 2015, 
2018). Both species are schooling clupeids pursued by a 
large, commercial purse seine fishery, called the reduction 
fishery. Additionally, a smaller bait fishery pursues Atlantic 
menhaden and captures about a quarter of the coastwide 
catch in U.S. waters of the Atlantic Ocean (SEDAR, 2015). 
Atlantic menhaden are caught along the Atlantic coast of 
the United States, mainly from Virginia to New Jersey. Gulf 
menhaden are taken in the Gulf of Mexico with most of the 
catch coming from the waters of Louisiana and Mississippi. 
These 2 fisheries are the largest by volume on their respec- 
tive coasts and together compose the second-largest fishery 
by volume in the United States (NMFS). Both species are 
important forage species and are eaten by other popular 
game fish species. The stock assessments for each species 
are reliant on the age data that have been provided from 
the Beaufort Laboratory of the NOAA Southeast Fisheries 
Science Center since 1955 for Atlantic menhaden and since 
1964 for Gulf menhaden. 
Aging of fish must evolve with time and technology, while 
continuity of data for long-term sampling programs is 
maintained. Traditionally, for both menhaden species, read- 
ings of scales to estimate ages were done at the Beaufort 
Laboratory by using an Eberbach® projector (Eberbach 
Corp., Ann Arbor, MI) that was built in the 1930s. However, 
the projector and its components are now obsolete, and 
replacement components are difficult to find. Given the 
challenges and risks of failure that arise from the use of 
obsolete equipment, alternative aging methods needed to 
be established. The objective of this study was to determine 
if ages for Atlantic and Gulf menhaden estimated by using 
a stereo microscope would be similar to those determined 
by using the Eberbach projector, with particular emphasis 
on precision or repeatability and on bias in age estimates 
between devices and methods. The aim of this study was to 
provide an alternative, more accessible method for aging 
menhaden in the future, a method that will decrease the 
likelihood of system failure as well as allow digital storage 
of sample images and information. 
Materials and methods 
Scales for this study were obtained from a long-term mon- 
itoring program that regularly samples landings of both 
the reduction and bait fisheries, in a 2-stage cluster design 
at various processing plants and dock locations along the 
Atlantic and Gulf coasts, geographically and temporally 
covering the entirety of the combined fishery (SEDAR, 
2015, 2018). Samples used for this study were collected 
in 2013 and 2017 for Atlantic menhaden and in 2005 and 
2 NMFS (National Marine Fisheries Service). 2018. Fisheries of 
the United States, 2017. NOAA, Natl. Mar. Fish. Serv., Curr. 
Fish. Stat. 2017, 142 p. [Available from website.] 
3 Mention of trade names or commercial companies is for identi- 
fication purposes only and does not imply endorsement by the 
National Marine Fisheries Service, NOAA. 
2017 for Gulf menhaden. Port agents retrieved a bucket 
of fish from the top of a randomly selected vessel’s fish- 
hold dockside to characterize the fish caught in the final 
set of the trip. The agent verified catch data and then 
selected 10 fish at random from the bucket and recorded 
fork length (in millimeters) and weight (in grams). From 
the 10 fish, scales were removed from an area centered 
in line with the foremost part of the dorsal fin along the 
lateral line. For each individual fish, 6-10 scales were 
cleaned and mounted between 2 glass microscope slides. 
Each scale sample was labeled by processing plant (if from 
the reduction fishery) or state (if from the bait fishery) 
and by year and was assigned a scale number or ID code. 
All scale samples were then used to estimate fish ages 
with an Eberbach projector and with a stereo microscope 
(Olympus SZX16, Olympus Corp., Tokyo, Japan). 
Age was determined by counting the number of contin- 
uous annuli between the focus and edge of the scale and 
by considering marginal growth as well as size, capture 
date, and each species’ conventional birth date, a stan- 
dard practice in some systems for the estimation of ages 
of fish sampled from commercial catches over a series 
of years (production aging) and in the Beaufort Labo- 
ratory menhaden program since the 1960s (June and 
Roithmayr, 1960; Nicholson and Schaaf, 1978; Morison 
et al., 1998; VanderKooy’). The additional information 
was important to help place fish in the proper cohort 
(O’Sullivan*), given the protracted spawning seasons of 
these species, and to provide better, more timely age esti- 
mates (Campana, 2001). 
For age estimation done with the Eberbach projector, 
mounted scale samples were placed under the projector’s 
objective (40x magnification), and the best scale was cho- 
sen for aging. Ages were recorded on a data sheet. If all 
scales were unreadable or if data were missing for a fish, 
the sample for that fish was excluded. 
The same scale samples used in aging with the Eber- 
bach projecter were observed by using a stereo microscope 
(7.5-16.0x magnification). An image of the best scale on 
each slide was taken by using image analysis software 
(cellSens, vers. 1.17, Olympus Corp.). Time between read- 
ings with the Eberbach projector and with the microscope 
for the primary reader (reader 1) varied from a few weeks 
to 3 years. Time between readings was the result of equip- 
ment and reader availability, sample selection intervals, 
and elapsed time between first readings during standard 
production aging for the long-term sampling program and 
the second readings for this study. 
All scale samples were read on both instruments, and 
some were read by 2 readers. For Atlantic menhaden, sam- 
ples were from fish caught in 2013 and 2017 and from the 
reference collection for this species at the Beaufort Labora- 
tory. For Gulf menhaden, samples were from fish caught in 
2005 and 2017 and from the reference collection for this 
species. These reference collections are sets of quality scale 
* O'Sullivan, S. 2007. Fisheries long term monitoring program— 
fish age estimation review, 22 p. Dep. Prim. Ind. Fish., Brisbane, 
Australia. [Available from website.] 
