47 
NOAA 
National Marine 
Fisheries Service 
Abstract— Multiple structures can 
be used for the age determination of 
fishes. Choosing the structure that 
provides the most precise ages is 
important for the provision of con- 
sistent data for the management of 
commercially and recreationally im- 
portant species, such as the Ameri- 
can shad (Alosa sapidissima). In this 
study, we compared the precision of 
age estimates obtained from sagit- 
tal otoliths, vertebrae, scales, and 
opercula as structures for the age 
determination of American shad. 
Two readers examined structures 
removed from 462 American shad, 
which were collected from the Mer- 
rimack River in Lawrence, Massa- 
chusetts, during May and June of 
2008-2010. The precision of age es- 
timates were evaluated by compari- 
sons of ages from different readers 
and structures. Age estimates deter- 
mined from otoliths were the most 
precise (76.2% agreement, 2.99% co- 
efficient of variation). Ages derived 
from scales were overestimated in 
young (<5 years) fish and underesti- 
mated in older (>7 years) fish, com- 
pared with ages determined from 
otoliths. Age estimates determined 
from vertebrae agreed with those ob- 
tained from otoliths better than ages 
from any other structure tested, but 
they were less precise and vertebrae 
required more processing than oto- 
liths. Opercula were difficult to read, 
resulting in underestimation of the 
ages of fish that were age 5 and old- 
er. The results of this study indicate 
that the sagittal otolith is the most 
appropriate structure for determin- 
ing the age of American shad. 
Manuscript submitted 25 October 2013. 
Manuscript accepted 25 November 2014. 
Fish. Bull. 113:47-54 (2015). 
doi: 10.7755/FB.113.1.5 
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. 
Fishery Bulletin 
& established 1881 -<?. 
Spencer F. Baird 
First U S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Comparison of 4 aging structures in the 
American shad {Alosa sapidissima ) 
Scott P. Elzey (contact author) 
Katie A. Rogers 
Kimberly J. Trull 
Email address for contact author: scott.elzey@state.ma.us 
Fish Biology Program 
Massachusetts Division of Marine Fisheries 
30 Emerson Avenue 
Gloucester, Massachusetts 01930 
The American shad ( Alosa sapidis- 
sima) is an anadromous fish found 
from the Gulf of St. Lawrence in Can- 
ada to the St. Johns River in Florida 
(Walburg and Nichols, 1967; Hassle- 
man et al., 2013). It is the largest 
species of the family Clupeidae found 
in waters of the United States (Wal- 
burg and Nichols, 1967), and individ- 
uals commonly reach sizes of 50 cm 
in total length (TL) (Scott and Leim, 
1966; Scott and Scott, 1988; Collette 
and Klein-MacPhee, 2002). This spe- 
cies spends most of its life in saltwa- 
ter but returns to freshwater rivers 
and streams in the spring to spawn. 
Most individuals return to spawn for 
the first time at age 4 or 5 (Walburg 
and Nichols, 1967; Scott and Leim, 
1966; Leggett and Carscadden, 1978; 
Ross, 1991). 
The American shad is a culturally 
and ecologically important species. 
This shad is a sought after game fish 
by recreational anglers, who prize it 
for its roe. It also composes an im- 
portant forage base for many species 
of fishes (Ross, 1991). Populations of 
American shad have declined because 
of fishing pressure and dams that 
have caused a loss of access to their 
spawning grounds (Ross, 1991; La- 
tour et al., 2012; Raabe and Hightow- 
er, 2014). These factors all make man- 
agement of American shad important. 
American shad are commonly 
aged by Cating’s (1953) scale tech- 
nique, in which counts of transverse 
grooves are used to identify the most 
probable locations of annuli. Recent 
studies have discredited the accuracy 
of this method (McBride et al., 2005; 
Duffy et al., 2011, 2012; Upton et al., 
2012). Recently, the use of otoliths to 
age American shad has been evalu- 
ated and validated as accurate with 
fish of known age for ages 3-9 (Duffy 
et al., 2012). However, Beamish and 
McFarlane (1983) have recommended 
validation of an aging technique for 
all reported ages and an exploration 
of alternative aging structures. 
The choice of aging structure is 
critical because not all structures 
are suitable for age determination 
of a given species. For example, al- 
though scales were historically used 
to age the white sucker (Catostomus 
commersonii), Beamish and Harvey 
(1969), after verifying yearly deposi- 
tion of annuli, found that pectoral- 
fin rays yielded older ages than did 
scales of individuals older than age 
5. Later studies on white suckers 
found that fin rays yielded biased 
ages in the oldest individuals and 
that the otolith was the most ap- 
propriate structure (Thompson and 
Beckman, 1995; Sylvester and Berry, 
2006). These examples show the im- 
portance of evaluating each structure 
for age determination. 
