Fang et al.: Age, growth, and population structure of Ommastrephes bartramii in the North Pacific Ocean 
41 
600 
550 
g" 500 
E 
— 450 
sz 
P 400 
Q 
_oj 350 
« 300 
250 
200 
150 
100 
150 
200 250 
Age (d) 
300 
350 
Figure 5 
Comparison of growth curves in relation to mantle length (ML) 
and age for red flying squid (Ommastrephes bartramii) from dif- 
ferent studies of the age and growth of this species. 
estimated from statolith growth increments (Yatsu et 
al., 1997; Yatsu, 2000). 
In a previous study, hatching time was estimated to 
be from January through April, indicating that samples 
belonged to the winter-spring cohort (Chen and Chiu, 
2003). The winter-spring cohort inhabits traditional 
fishing grounds (150° to 170°E) in the Northwest Pa- 
cific (Bower and Ichii, 2005). We obtained results for 
hatching time, using a back-calculation based on up- 
per beak increments, and our results were similar to 
estimates from statoliths for squid caught in a similar 
area and time during a previous study (Chen et al., 
2011). Meanwhile, age were validated for the same spe- 
cies by using statoliths and beaks (Liu et al., 2015). 
The results from that previous study showed that beak 
increments had a high correlation with statolith incre- 
ments for red flying squid: beak increments=1.0177xs- 
tatolith increments - 6.6795 (r 2 =0.969, n=21, P<0.001) 
(Liu et al., 2015). Therefore, we conclude that the beak 
is a hard structure that can be used reliably for age 
determination of ommasterphid species. 
Females and males presented a similar growth pat- 
tern during ontogenesis (Table 1, Fig. 4). This finding 
differs from the observation of Chen et al. (2011), who 
suggested that females grow faster than males in ev- 
ery age class and that the peak growth rates occur 
in a relatively younger age class (140-220 d) (Chen 
et al., 2011). Sexual asynchrony of growth for red fly- 
ing squid at different life stages also was found by 
Yatsu et al. (1997) and Brunetti et al. (2006). Chen 
and Chiu (2003) analyzed the growth of 2 geographi- 
cally distinct stocks of red flying squid in the North 
Pacific Ocean and divided the females into 2 groups: 
large-size (>350 mm ML) and small-size (<350 mm 
ML) females. They found that small-size females in 
the northwestern stock had a growth mode that was 
similar to that of males that can be described 
best with a Gompertz function, but large-size 
females in the northwestern stock grew much 
faster than males in either stock. Therefore, 
the female samples in our study may belong 
to the small-size group of females in the nor- 
thwestern stock — a possibility that could ex- 
plain the nearly synchronous growth between 
sexes. It is also notable that the ML DGR for 
males was much lower than that for fema- 
les after ages 301-350 d (Fig. 4). The reason 
for this difference may be the greater energy 
need of females to support their metabolism 
during gametogenesis (Rocha et al., 2001). 
There was no significant difference in 
growth curves between the 2 sexes, accord- 
ing to the results of ANCOVA (P> 0.05). Ex- 
ponential curves seem to be appropriate for 
ML-age and BW-age relationships, whereas 
a linear curve was suitable for the URL-age 
relationship, although it showed a low correla- 
tion between the two variables. Different rela- 
tionships between age and ML and BW have 
been found with various techniques in previous 
studies (e.g., exponential model for paralarve, Bigelow 
and Landgraph, 1993; Yatsu, 2000; linear model, Yatsu 
et al., 1997, Chen et al., 2011; Gompertz model, Chen 
and Chiu, 2003). The exponential curve is a logical 
choice for describing the very fast growth rate of squid, 
especially for paralarve (Bigelow and Landgraph, 1993; 
Sakai et al., 1999, 2006; Yatsu, 2000). 
We also compared the growth curves for adult red 
flying squid with those derived from 2 other studies, 
and we found that our reported growth rate was rela- 
tively lower than those rates in the other 2 studies 
(Fig. 5). There are 2 potential reasons for this differ- 
ence: 1) the female squids in this study belonged to 
the group of small-size females in the northwestern 
stock (Chen and Chiu, 2003), a group that tends to 
have a low growth rate than that of the squid used in 
the other 2 studies, especially in the study by Yatsu 
et al. (1997), whose samples may have belonged to 
large-size females of that stock, and 2) the size and 
life span of squid can be influenced by ambient tem- 
perature, an influence that is more obvious in extreme 
weather (e.g., El Nino or La Nina), as has been docu- 
mented for the jumbo squid ( Dosidicus gigas ) (Arkh- 
ipkin et al., 2015). 
Compared with squid in our 2011 study, squid in 
previous studies tended to attain larger sizes but have 
a shorter life span (in years) with warm temperatures 
(i.e., squid hatched during 1991-1993 for Yatsu’s [2000] 
study and in 1997 for Chen and Chiu’s [2003] study) 
and to attain smaller sizes but a long life span with 
cold temperatures (i.e., squid hatched in 2007 for the 
Chen et al. [2011] study). However, model selection can 
be influenced by sample size and sampling range. Ad- 
ditional sampling and a greater size range of individu- 
als will be needed to evaluate growth functions more 
thoroughly. 
