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Fishery Bulletin 109(4) 
B 
E 
primordium 
rostrum 
width 
Figure 2 
Otolith features and landmarks for morphometric measurements of Pacific sardine 
( Sardinops sagax ). (A) Pacific Northwest specimen, age-0, 1.9 mm long, with a 
relatively smooth perimeter. (B) Gulf of California specimen, age-1, 3.1 mm long, 
with a relatively lobed perimeter. (C) Features for morphometry. Length is the 
distance from the midpoint of the rostrum at point A through the primordium 
to the posterior edge at point B. Width is the distance perpendicular to the 
length passing through the primordium. CE is the distance from the tip of the 
antirostrum to the ventral edge, parallel to the width; CC’ is the segment of 
CE that represents the gap between the antirostrum (point C) and the rostrum; 
and D is the notch between the antirostrum and the rostrum. 
mark points on the perimeter and through the primor- 
dium. The perimeter may develop rounded, irregular, 
or dentate protuberances, particularly along the ven- 
tral side, such that some otoliths are relatively smooth 
and others are relatively lobed (Fig. 2, A and B). Sag- 
ittal otoliths composed of vaterite, which are always 
clear and highly lobate, were omitted from the study. 
We used both left and right otoliths. Age was deter- 
mined by the method of Yaremko (1996). Age-1 otoliths 
weigh 0.73-1.30 mg based on our unpublished aging 
studies. After having been cleaned in distilled water, 
otoliths were dried, weighed on a Cahn C-33 micro- 
balance (Thermo Electron Corp., Marietta, OH) with 
0.005 mg accuracy and photographed with a reference 
scale for measuring otolith dimensions with Image-Pro 
Plus, vers. 4.5.1 or 6.3 software (Media Cybernetics, 
Inc., Bethesda, MD). The length (segment AB, Fig. 2C) 
was determined first, from the midpoint on the ros- 
trum tip through the primordium to the posterior edge. 
Three segments perpendicular to the length included 
the width through the primordium, segment CE, and 
CE subsegment C-C’ (a measure of the gap between 
the rostrum and antirostrum [point C] ). Point D was 
the notch between the rostrum and the antirostrum. 
Other measured segments included AC, AD, BC, and 
BD. In addition to weight, the measurements included 
eight straight linear dimensions, perimeter, and area. 
The autotrace function of the software determined the 
perimeter and area. 
Northern vs. southern California sardine populations 
A synoptic study for 2006-07 of age-1 cohorts that 
turned age-2 during the spring of the calendar year 
was conducted to compare regional differences in sardine 
otoliths from Monterey Bay and from San Diego, about 
700 km apart. Sardine from both regions presumably 
share the same spawning area offshore from central 
