50 
National Marine 
Fisheries Service 
NOAA 
Fishery Bulletin 
o- established In 1881 ■<?. 
Spencer F. Baird 
First U S Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Geographic variations of jumbo squid (Dosidicus 
gigas ) based on gladius morphology 
2 The Key Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources 
Ministry of Education 
999 Huchenghuan Road 
Shanghai 201306, China 
3 National Engineering Research Centre for Oceanic Fisheries 
Shanghai Ocean University 
999 Huchenghuan Road 
Shanghai 201306, China 
4 National Demonstration Center for Experimental Fisheries Science Education 
Shanghai Ocean University 
999 Huchenghuan Road 
Shanghai 201306, China 
Abstract —The jumbo flying squid 
(Dosidicus gigas ) is widely distribut¬ 
ed in the eastern Pacific Ocean and 
its population structure is complex. 
Morphometric analysis of hard struc¬ 
tures of cephalopods is frequently 
employed to explore the geographic 
variation within discreet population 
units. In this study, 8 morphometric 
characteristics of the gladius, or pen, 
were measured and compared from 
562 jumbo squid specimens collected 
off Peru, the Costa Rica Dome, and 
from the equatorial central eastern 
Pacific. The growth rate of the gla¬ 
dius was evaluated by comparing 
it with the ages determined from 
statoliths. Results showed signifi¬ 
cant differences in gladii morphol¬ 
ogy between sexes and geographic 
populations. Stepwise discriminant 
analysis indicated that gladius mor¬ 
phometric characteristics were suit¬ 
able discriminatory variables with 
an overall correct classification rate 
of 78.6% for distinguishing different 
populations. Higher daily growth 
rates were found in the proostracum 
than in the conus, possibly because 
of the different biological functions 
of these anatomical parts. These re¬ 
sults support our general hypothesis 
that gladius morphology provides 
an alternative way to distinguish 
potential geographic populations of 
D. gigas and it adds new informa¬ 
tion regarding the gladius of the 
Ommastrephidae. 
Manuscript submitted 3 March 2017. 
Manuscript accepted 7 November 2017. 
Fish. Bull. 116:50-59 (2018). 
Online publication date: 7 December 2017. 
doi: 10.7755/FB.116.1.5 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Yi Gong 1 
Xinjun Chen 1 ' 2 ' 3 4 
Yunkai Li (contact author) 1 - 2 ' 3 ' 4 
Zhou Fang 1 
Email address for contact author: ykii@shou.edu.cn 
1 College of Marine Sciences 
Shanghai Ocean University 
999 Huchenghuan Road 
Shanghai, 201306, China 
Morphometric analysis has been an 
accepted method for studying the 
geographic variation of population 
units within species of cephalopods 
(Nesis, 1993; Crespi-Abril et al., 
2010; Liu et al., 2015a; van der Vyver 
et al., 2016). Cephalopods show high 
phenotypic plasticity in both soft and 
hard structures owing to their bio¬ 
logical characteristics, such as rapid 
growth, short life span, and highly 
migratory activity (Crespi-Abril et 
al., 2010; Arkhipkin et al., 2015; van 
der Vyver et al., 2016). Therefore, 
morphometric analysis may be a use¬ 
ful approach for studying geographic 
variations in pelagic cephalopods 
that have an extensive distribution 
range. 
The jumbo flying squid ( Dosidi¬ 
cus gigas ) is widely distributed in 
the eastern Pacific Ocean, extending 
from Alaska (60°N) to Chile (46°S) 
and stretching to the west (125°- 
140°W) at the Equator (Nigmatul- 
lin et al., 2001; Ibanez and Cubil- 
los, 2007). As a pelagic cephalopod, 
D. gigas has an important ecological 
function in marine ecosystems, not 
only as a voracious predator but also 
as a valuable source of prey (Field et 
al., 2007; Alegre et al., 2014). It also 
supports an important commercial 
fishery, and in 2014 the annual catch 
exceeded 1,000,000 metric tons (FAO, 
2016). The main fishing regions are 
located off the coasts of Chile and 
Peru, off the Costa Rica Dome and 
within the Gulf of California. 
Throughout its geographic range, 
the population structure of D. gigas 
is complicated and often debated. 
In the past, three distinguishable 
groups with a different size-at-ma- 
