Begg et al: Use of otolith morphometries for identification of stocks of Me/anogrammus aeglefinus 
9 
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Figure 5 
Scatter plots of internal otolith morphometric variables for 4-year-old haddock ( 1993 year class) show- 
ing grouping patterns of eastern Georges Bank (squares) and western Georges Bank (circles). 
studies (Campana and Neilson, 1985; Mosegaard et al., 
1988; Campana and Casselman, 1993), although there 
may also be a genetic contribution (Gauldie and Nelson, 
1990; Friedland and Reddin, 1994). 
The eastern and western Georges Bank spawning com- 
ponents, therefore, probably comprise phenotypically sepa- 
rate individuals that reflect differences in otolith structure 
due to environmental variation. These types of morpholog- 
ical differences indicate growth rate differences linked to 
the environment, rather than any genetic differences. Our 
results concur with previous studies that indicate sepa- 
rate spawning components on Georges Bank (Smith and 
Morse, 1985; Begg et al., 1999; Begg and Brown, 2000), 
although the degree of connectivity between the two com- 
ponents is not known. Larvae spawned on the Northeast 
Peak recruit to the central part of the Bank as they de- 
velop and are advected from there along its southern flank 
(Lough and Bolz 1989), whereas some larvae spawned 
throughout the Great South Channel are advected along 
the northern flank, with the result that there is some mix- 
ing between progeny. Further studies need to examine 
mixing rates and spawning-site fidelity of individual fish 
originating from the eastern and western Georges Bank 
spawning components in order to determine if there is an 
underlying genetic basis for stock separation. 
Analysis of internal otolith morphometries may provide 
a more detailed description of individual fish stocks than 
morphometric analysis of whole otoliths because the use 
of internal otolith morphometries specifically incorporates 
individual growth zones, as well as characteristic shape 
qualifiers. Measurement of the first growth zone in whole 
otoliths has commonly been used in stock identification 
studies, although the results have been far from conclu- 
sive (e.g. Dawson, 1991; Hopkins 4 ; Marecos 5 ). Likewise, 
mixed results have been found for microstructure anal- 
ysis of otolith nuclear dimensions and growth incremen- 
tal widths (e.g. Rybock et al., 1975; Neilson et al., 1985; 
Mosegaard and Madsen 6 ). Certainly, the use of more than 
one growth or shape dimension improved our ability to 
identify groups, but the utility or cost-effectiveness of in- 
ternal otolith morphometries may be questioned when 
compared to shape analysis of whole otoliths. 
4 Hopkins, P. J. 1986. Mackerel stock discrimination using oto- 
lith morphometries. ICES CM 1986/H 7, 16 p. 
5 Marecos, M. L. 1986. Preliminary analysis of horse mackerel 
( Trachurus trachurus L. ) otolith (LI ) measurements. ICES CM 
1986/H 72, 8 p. 
6 Mosegaard, H., and K. P. Madsen. 1996. Discrimination of 
mixed herring stocks in the North Sea using vertebral counts 
and otolith microstructure. ICES CM 1996/H 17, 8 p. 
