Javor et al.: Otolith morphometries and population structure of Sardmops sagax along the west coast of North America 
413 
was also an important factor (Tuset et al., 2006; Jons- 
dottir et al., 2006). In a morphometric study of Pacific 
sardine otoliths from Baja California, Mexico, Felix- 
Uraga et al. (2005) used length and other linear dimen- 
sions, but not area, perimeter, or weight. Because these 
factors were the most important in the first principal 
component that explained most of the variance in the 
present investigation, a re-evaluation of those otoliths 
might refine the results of the earlier study. However, 
those otoliths were permanently mounted on slides in 
clear resin that precluded weighing them and obtaining 
sharp digital images to measure area and perimeter 
with the autotrace tool of the image-processing software 
(R. Felix-Uraga 1 ). 
Both temperature and growth rate can be factors 
influencing otolith shape. In a study of two stocks of 
silver hake (Merluccius bilinearis), fish in the north- 
ern stock grew slower, probably due to colder tempera- 
tures, and their otoliths were subsequently larger (i.e., 
older) than those from southern-stock fish of the same 
standard length (Bolles and Begg, 2000). Similar phe- 
nomena have been noted in other fish (summarized by 
Strelcheck et al., 2003). Hussy (2008) showed higher 
food consumption resulted in a higher number of lobes 
in otoliths of juvenile Atlantic cod ( Gadus morhua). 
In our 2006-07 synoptic study of region 3 and 4 co- 
horts, we found no apparent growth differences be- 
tween recruits captured near Monterey and San Diego, 
although the higher percentage of smoother otoliths in 
Monterey was notable. Juveniles from both locations are 
believed to come from central and southern California 
coastal spawning grounds (Lo et al., 2005). An obvious 
explanation for the differences in otolith morphometries 
between the two regions may be temperature. 
Temperature has been tested and shown to affect 
otolith growth characteristics in other species. Posi- 
tive effects of temperature on otolith weight have been 
observed in red drum ( Sciaenops ocellatus) (Hoff and 
Fuiman, 1993) and herring ( Clupea harengus ) (Fey, 
2001). Flounder ( Paralichthys olivaceus) otoliths showed 
no significant difference in marginal coarseness be- 
tween wild fish and experimental fish maintained at 
15°, 20°, and 25°C (Katayama and Isshiki, 2007). Hoff 
and Fuiman suggested that otolith growth was more 
directly affected by metabolic rate than by growth rate. 
Our unpublished data indicate that otolith weights 
and perimeters of sardine reared in tanks at different 
temperatures are dissimilar to those same variables 
in otoliths of wild-caught sardine of the same age and 
they likely reflect artifacts of aquaculture that may be 
independent of water temperature. 
Temperature may affect sardine otolith morphomet- 
ries in wild populations, but other factors may modify 
them. An improved survey to address possible tempera- 
ture effects would compare all sardine sizes from their 
environmental ranges. Sardine do not regularly spawn 
1 Felix-Uraga, Roberto. 2005. Personal commun. Centro 
Interdisciplinario de Ciencias Marinas, La Paz, Baja Cali- 
fornia Sur, Mexico. 
successfully in the Pacific Northwest (McFarlane and 
Beamish, 2001; Emmett et al., 2005; Lo et al., 2010), 
and therefore further study to elucidate the environ- 
mental or growth factors that contribute to regional 
differences in otolith morphometries in cold ocean en- 
vironments would be hampered by the availability of 
samples of young fish. Likewise, older sardine are not 
usually collected in warmer Mexican waters. 
Conclusion 
Results from MANOVA indicated there were regional 
differences in age-1 otoliths between regions or clusters 
of regions when nearly 700 fish were compared. Based 
on comparisons with average otoliths of the same length 
or area, PWPs of young and adult sardine otoliths 
coupled with MANOVA and chi-square tests showed 
differences among some regions, as well as significant 
similarities. This investigation provided further evi- 
dence that S. sagax populations in their southernmost 
distribution in Mexican waters are a distinct stock 
from U.S. and Canadian populations (Felix-Uraga et 
al., 2004, 2005; Smith, 2005). Sardine from Ensenada 
(region 5) shared otolith features with both southern 
and northern stocks. Age-1 otoliths from northern 
California (region 3) tended to be heavier and smoother 
than those from other areas. Some regions showed 
variations in PWPs between years. PWPs were useful 
for describing relationships between and within local 
and regional sardine stocks and age cohorts. PWPs 
can be applied as a tool for understanding residence, 
migration, and population connectivity when used in 
combination with otolith chemistry, aging, genetics, and 
other traditional measures of population structures for 
sardine and other species of fish. 
Acknowledgments 
We gratefully acknowledge the individuals and agencies 
listed in Table 1 for the extensive collections of sardine 
otoliths. We thank L. Robertson of the NOAA Southwest 
Fisheries Science Center for monthly collections from 
the bait supplier for otolith extraction, and Z. Fan and 
Y. Gu for statistical analyses. We thank J. Hyde, M. 
Lowry, and J. Stewart for helpful reviews of early drafts 
of the manuscript. 
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Bolles, K. L., and G. A. Begg. 
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