Abstract— Internal otolith morpho- 
metries, coupled with image analysis 
procedures and multivariate statistical 
analyses, were examined to investigate 
stock structure of haddock ( Melano - 
grammus aeglefinus) on Georges Bank 
in the northwest Atlantic. Samples were 
collected during spring 1995-97 from 
the Northeast Peak (eastern Georges 
Bank) and the Great South Channel 
(western Georges Bank) spawning com- 
ponents. The structure of transverse 
sagittal otolith sections were described 
for individual haddock samples from 
each spawning component by using a 
combination of linear morphometries, 
shape characteristics, and growth incre- 
ments. Analyses were structured to 
account for the effects of size, sex, age, 
and year class. Significant differences 
in internal otolith structure were found 
between eastern and western Georges 
Bank haddock, providing phenotypic 
evidence of stock separation between 
the two spawning components. East- 
ern Georges Bank haddock tended to 
have smaller internal otolith dimen- 
sions than western Georges Bank had- 
dock; these differences appeared to be 
related to growth rates. Total classifi- 
cation success for each spawning com- 
ponent varied from 61% to 83% for 
the different age and year-class combi- 
nations. Results from this study may 
be helpful in forming consistent stock 
definitions that can be used by both 
U.S. and Canadian fishery management 
agencies for rebuilding stocks of had- 
dock on Georges Bank. 
Manuscript accepted 29 June 2000. 
Fish. Bull. 99:1-14 (2001). 
The use of internal otolith morphometries 
for identification of haddock 
l Melanogrammus aeglefinus) 
stocks on Georges Bank 
Gavin A. Begg 
William J. Overholtz 
Nancy J. Munroe 
Northeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
166 Water Street 
Woods Hole, Massachusetts 02543 
Present address (for G. A. Begg): Marine Research Institute 
PO Box 1390 
121 Reykiavik, Iceland 
E-mail address (for G A Begg) gavm@hafro.is 
Otoliths are crystalline structures com- 
posed of calcium carbonate and are ideal 
structures for use in fish stock iden- 
tification, containing a range of mea- 
surable characteristics including linear 
and shape morphometries, optical den- 
sity, and microstructural zonation and 
growth patterns, and elemental constit- 
uents (Ihssen et al., 1981; Campana 
and Neilson, 1985; Pawson and Jen- 
nings, 1996). Otoliths grow throughout 
the life of fish, are metabolically inert, 
and are typically available as a his- 
torical time series because of routine 
age and growth assessments (Campana 
and Neilson, 1985; Campana and Cas- 
selman, 1993). 
Linear and shape morphometries of 
otoliths have been widely used for fish 
stock identification (e.g. Messieh et ah, 
1989; Dawson, 1991; Smith, 1992; Cam- 
pana and Casselman, 1993; Friedland 
and Reddin, 1994), although their use 
has been questioned because of within- 
stock differences in sex, age, and year- 
class variation ( Castonguay et ah , 199 1 ; 
Begg and Brown, 2000). Moreover, oto- 
lith morphometries have been found 
to be strongly correlated with growth, 
which influences development of oto- 
lith crystalline microstructure (Smith, 
1992; Campana and Casselman, 1993). 
Stock definitions based on differences 
in otolith structure, therefore, depend 
not only on differential growth rates, 
but on the consistency of the environ- 
ment integrated over the life history of 
fish in each stock (Campana and Cas- 
selman, 1993). Although otolith mor- 
phometries cannot be used to differen- 
tiate stocks on a genetic basis, they can 
provide a phenotypic basis for stock 
separation that is useful for fisheries 
management (Casselman et al., 1981; 
Begg and Waldinan, 1999). 
Fisheries management is moving to- 
wards a precautionary approach to en- 
sure sustainable utilization of our ma- 
rine resources (FAO, 1995; ICES 1 ). One 
requirement of the precautionary ap- 
proach is to consider the full impact of 
management actions, including explicit 
consideration of stock complexity (Gar- 
cia and Grainger, 1997). For this rea- 
son, there is a growing interest in the 
importance and recognition of individu- 
al spawning components within histor- 
ically established management units 
(FAO, 1995; Stephenson, 1999). 
The importance of individual spawn- 
ing components has been acknowledged 
in the management of haddock, Mela- 
nogrammus aeglefinus , a commercially 
important groundfish of the northwest 
Atlantic. The interest in haddock stock 
complexity is exemplified on Georges 
Bank (Fig. 1 ), where this species forms 
an important transboundary resource 
among U.S. and Canadian fishermen 
(Halhday and Pinhorn, 1990; Begg, 
1 ICES (International Council for the Explo- 
ration of the Sea). 1997. Report of the 
study group on the precautionary approach 
to fisheries management. ICES council 
meeting (CM) 1997/assess 7, 41 p. 
