Gong et al.: Geographic variations in the distribution Dosidicus gigas 
57 
Table 6 
Absolute daily growth rates (DGR) in mm/day for conus length (CL) and proostracum lengh 
(PL) for female and male jumbo squid (Dosidicus gigas) sampled off the Costa Rica Dome 
(CRD), off the Peruvian exclusive economic zone (PE), and in offshore waters of the central 
eastern Pacific (CEP) in 2009, 2013, and 2014. «=number of squid in a sample. na=data not 
available. 
Population 
Sex 
Age class 
(d) 
n 
Average 
CL (mm) 
DGR 
(mm/d) 
Average 
PL (mm) 
DGR 
(mm/d) 
CR 
F 
126-150 
2 
37.5 
na 
167.5 
na 
151-175 
15 
43.1 
0.22 
198.0 
1.22 
176-200 
36 
49.2 
0.24 
222.9 
1.00 
201-225 
29 
57.9 
0.35 
259.0 
1.44 
226-250 
3 
63.0 
0.20 
288.0 
1.16 
PE 
F 
126-150 
8 
46.0 
na 
188.0 
na 
151-175 
31 
49.2 
0.13 
200.6 
0.50 
176-200 
41 
51.9 
0.11 
211.0 
0.42 
201-225 
7 
62.1 
0.41 
239.0 
1.12 
226-250 
2 
68.5 
0.26 
255.5 
0.66 
251-275 
2 
78.0 
0.38 
278.5 
0.92 
M 
126-150 
6 
42.5 
na 
186.3 
na 
151-175 
17 
47.3 
0.19 
194.8 
0.34 
176-200 
21 
49.8 
0.10 
204.2 
0.38 
201-225 
8 
60.1 
0.41 
233.4 
1.17 
CEP 
F 
126-150 
5 
50.6 
na 
191.6 
na 
151-175 
6 
54.7 
0.16 
208.3 
0.67 
176-200 
26 
59.7 
0.20 
236.0 
1.11 
201-225 
12 
65.8 
0.24 
250.7 
0.59 
226-250 
4 
69.5 
0.15 
276.0 
1.01 
M 
126-150 
5 
45.8 
na 
185.0 
na 
151-175 
13 
51.6 
0.23 
200.5 
0.62 
176-200 
27 
60.1 
0.34 
234.7 
1.37 
201-225 
13 
64.5 
0.18 
252.50 
0.71 
226-250 
1 
67.0 
0.10 
268.00 
0.62 
2011; Staaf et al., 2011). The proostracum contributes 
to a large proportion of GL (>80 %) and has a higher 
longitudinal growth rate than conus (Table 6). With the 
assumption that the conus provides a supporting struc¬ 
ture for the fin during swimming, the higher growth 
rate of the proostracum can be considered a struc¬ 
ture that meets the requirements for rapid growth of 
squids because the gladius is a tissue that supports the 
growth of the mantle and internal organs (Bizikov and 
Arkhipkin, 1997; Arkhipkin et al., 2012). Comparisons 
in CL/PL values and growth rates between geographic 
populations show spatial variations in these two struc¬ 
tures. The squid from CEP had higher CL/PL values 
than the squid from the area of the CRD and PE. We 
suggest that this result is possibly due to the environ¬ 
mental conditions experienced by the squid off the CRD 
and PE that are reflected in the longitudinal growth of 
proostracum. The Humboldt Current or upwelling (or 
both) supply nutrients to the waters off Peru and the 
CRD, while the waters of the central equatorial Pacific 
have lower primary productivity (Anderson and Rod- 
house, 2001; Fiedler, 2002). Because food availability 
is considered as one of the central factors that influ¬ 
ences D. gigas growth (Chen et al., 2013; Liu et al., 
2013), regional differences in primary productivity may 
be strongly correlated with the observed differences in 
the growth of gladius. 
Although the squid populations can be distinguished 
on the basis of morphological evidence, there is still 
considerable overlap, as shown in Table 5, A and B, 
which suggests that stable population substructuring 
is not the norm. Similar overlap has also been observed 
in elemental signatures in statoliths o D. gigas from 
waters off the Costa Rica Dome and Peru (Liu et al., 
2015b). Indeed it was reported that a weak northern 
and southern hemisphere divergence was found for D. 
gigas with the use of molecular methods. Sandoval- 
Castellanos et al. (2010) and Staaf et al. (2010), and 
some of our results from CEP individuals have also in¬ 
dicated a close similarity to the other two jumbo squid 
populations. This finding would suggest that although 
the morphological studies reported here suggest clear 
spatial subpopulations, further research will reveal the 
stability of these populations units over time. 
