Fang et al.: Age, growth, and population structure of Ommastrephes bartramii in the North Pacific Ocean 
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Figure 2 
(A) Schematic diagram of the rostrum sagittal sections (RSS), the internal rostral axis (IRA), and upper 
rostral length (URL) in the beak of red flying squid (Ommastrephes bartramii). Photographic images of (B) 
a whole RSS and (C) IRA of a male individual with mantle length of 245 mm and age of 174 d, every blue 
dot represents one ring, and images with (D) longitudinal increments in the hood of the RSS of a female 
individual with mantle length of 390 mm and age of 268 d, every white line represents one ring, and (E) a 
check ring at 40x magnification. 
(400x) (Fig. 2D). The mean width of increments in the 
RSS was 12.6 pirn (standard deviation [SD] 0.03). 
In some atypical beak samples, we found “check” 
rings, which were similar to the rings in the micro- 
structure of the statolith (Fig. 2E). A check ring was 
an extremely light band that appeared in multiple in- 
crements. These types of increments were easy to dis- 
cern in comparison with the surrounding regular incre- 
ments. This structure occurred much more frequently 
in females than in males. 
Age composition and hatching time 
The total sample size was 211 Squid, of which 109 were 
females and 102 were males. The ML of females ranged 
from 199 to 417 mm (average=268 mm [SD 44]). The 
majority (85.4%) of females ranged from 240 to 320 
mm in ML. Male ML ranged from 201 to 354 mm (av- 
erage=248 mm [SD 33]); 85.4% males ranged from 240 
to 280 mm ML (Fig. 3A). Female BW ranged from 140 
to 2230 g (average=603 g [SD 353]); 72.7% of females 
