Staaf et al Distribution of ommastrephid paralarvae in the eastern tropical Pacific 
87 
This view clearly contrasts with the one originally 
proposed by Nesis (1983) in which the jumbo squid 
spawns in the ETP and then migrates to feed at higher 
latitudes in both hemispheres. Available genetic analy- 
sis instead indicates 2 separate breeding populations, 
1 in the northern hemisphere and 1 in the southern 
hemisphere (Staaf et al., 2010). If the preferred spawn- 
ing habitat of jumbo squid is indeed subtropical to tem- 
perate, rather than tropical, it could explain the divi- 
sion into 2 populations, 1 breeding off Mexico and 1 
breeding off Peru. 
For future collections, we recommend preservation of 
material from both oblique and surface tows in ethanol. 
Although we were able to extract and identify paralar- 
vae from frozen plankton samples, the technique has 
2 drawbacks: 1) the difficulty of visual identification 
of individual specimens in the thawed slurry and 2), 
if the samples are to be sorted in more than one ses- 
sion, the damage done to the entire sample by repeated 
freeze-thaw cycles. 
Conclusions 
We found paralarvae in surface and oblique tows to be 
of equal size, indicating that paralarvae of the 2 om- 
mastrephid species jumbo squid and purpleback squid 
do not engage in ontogenetic vertical migration at the 
paralarval stage. Ommastrephid paralarvae were much 
more abundant in surface tows than in oblique tows; 
this finding may indicate an ecological advantage of 
surface waters — perhaps, related to feeding. Models 
selected SST as the strongest predictor of paralarval 
presence in both surface and oblique tows; presence 
was more likely at higher temperatures. Therefore, 
warm surface waters appear to be the preferred habi- 
tat of ommastrephid paralarvae in the ETP. Molecu- 
lar identification of specimens from a small subset of 
oblique tows showed that paralarvae of purpleback 
squid far outnumbered those of jumbo squid in this 
region. Adults of purpleback squid are broadly dis- 
tributed in the tropics, whereas adult jumbo squid are 
abundant in tropical, subtropical, and temperate wa- 
ters and occasionally present in boreal waters. Results 
from this study are consistent with the possibility that 
the purpleback squid spawns primarily in the tropics, 
and the jumbo squid spawns preferentially in subtropi- 
cal or, perhaps, even temperate regions. 
Acknowledgments 
To the cruise coordinators, the net-towing oceanogra- 
phers, the plankton-sorting students and contractors, 
and the commanding officers and crew of the research 
vessels, we offer our boundless gratitude. We also thank 
P. Fiedler and staff at the Southwest Fisheries Science 
Center for processing oceanographic data, M. Ohman 
for providing ethanol-preserved samples and advice, A. 
Townsend for oversight of sample processing, L. Loren- 
zo for sample sorting, C. Elliger and Z. Lebaric for DNA 
sequencing, G. Watters for project guidance. We are 
also grateful for support from the Nancy Foster Schol- 
arship Program of NOAA (to DJS) and the National 
Science Foundation (OCE0526640 and OCE0850839 to 
WFG). 
Literature cited 
Aitchison, J. 
1955. On the distribution of a positive random variable 
having a discrete probability mass at the origin. J. Am. 
Stat. Assoc. 50:901-908. 
Ambrose, D. A., R. L. Charter, H. G. Moser, S. R. Charter, and 
W. Watson. 
2002a. Ichthyoplankton and station data for surface 
(manta) and oblique (bongo) plankton tows taken dur- 
ing a survey in the eastern tropical Pacific Ocean July 
30-December 9, 1998. NOAA Tech. Memo. NOAA-TM- 
NMFS-SWFSC-337, 126 p. 
Ambrose, D. A., R. L. Charter, H. G. Moser, B. S. MacCall, and 
W. Watson. 
2002b. Ichthyoplankton and station data for surface 
(manta) and oblique (bongo) plankton tows taken dur- 
ing a survey in the eastern tropical Pacific Ocean July 
28-December 9, 2000. NOAA Tech. Memo. NOAA-TM- 
NMFS-SWFSC-342, 130 p. 
Anderson, C., and P. G. Rodhouse. 
2001. Life cycles, oceanography and variability: ommas- 
trephid squid in variable oceanographic environments. 
Fish. Res. 54:133-143. 
Boletzky, S. v. 
2003. Biology of early life stages in cephalopod mol- 
luscs. Adv. Mar. Biol. 44:143-293. 
Brown, D. M., and L. Cheng. 
1981. New net for sampling the ocean surface. Mar. 
Ecol. Prog. Ser. 5:225-227. 
Camarillo-Coop, S., C. Salinas-Zavala, M. Manzano-Sarabia, 
and E. A. Aragon-Noriego. 
2011. Presence of Dosidicus gigas paralarvae (Cepha- 
lopoda: Ommastrephidae) in the central Gulf of Cali- 
fornia, Mexico related to oceanographic conditions. J. 
Mar. Biol. Assoc. U.K. 91:807-814. 
FAO (Food and Agriculture Organization of the United 
Nations). 
2011. FAO yearbook. Fishery and aquaculture statistics: 
2009, 78 p. FAO, Rome. 
Fernandez-Alamo, M. A., and J. Farber-Lorda. 
2006. Zooplankton and the oceanography of the eastern 
tropical Pacific: a review. Prog. Oceanogr. 69:318-359. 
Fiedler, P. C. 
2010. Comparison of objective descriptions of the ther- 
mocline. Limnol. Oceanogr. Methods 8:313-325. 
Fiedler, P. C., and L. D. Talley. 
2006. Hydrography of the eastern tropical Pacific: a re- 
view. Prog. Oceanogr. 69:143-180. 
Gilly, W. F., C. A. Elliger, C. A. Salinas, S. Camarillo-Coop, G. 
Bazzino, and M. Beman. 
2006. Spawning by jumbo squid ( Dosidicus gigas ) in the 
Pedro Martir Basin, Gulf of California, Mexico. Mar. 
Ecol. Prog. Ser. 313:125-133. 
