86 
Fishery Bulletin 1 1 1 (1) 
scattering layers. To our knowledge, such a dedicated 
effort to address this problem has not been reported. 
Oceanography 
The number of both bongo- and manta-net tows that 
contained paralarvae increased as SST increased from 
15°C to 32°C (Table 1, Fig. 3). This increased paralarval 
occurrence is consistent with the literature. Paralar- 
vae of purpleback squid exhibit a preference for warm 
temperatures (28-31°C) in waters off Japan (Saito and 
Kubodera, 1993), and extremely large numbers of SD- 
complex paralarvae in the ETP were captured in in- 
dividual tows coincident with the 29°C SST isotherm 
(Vecchione, 1999). In the Gulf of California, paralarvae 
of jumbo squid are more abundant during the warm 
months of June and September (SST of 27.7-29.4°C) 
than during the cooler season of February and April 
(SST of 15.3-18. 1°C) (Camarillo-Coop et ah, 2011). Be- 
cause our surveys were conducted only between late 
July and early December, we were unable to assess 
seasonal variability in paralarval distribution. 
We found no evidence for a decrease in paralarval 
occurrence at the highest SST values, despite the fact 
that embryonic development in vitro is optimal in the 
range of 17-25°C and fails to proceed at 30°C (Staaf et 
ah, 2011). The idea that paralarvae may be better able 
than developing embryos to withstand warmer tem- 
peratures would be consistent with a upward vertical 
migration after hatching. If hatchlings promptly swim 
from near the pycnocline up to warmer near-surface 
water, where food may be more readily available, an 
ontogenetic increase in temperature optima would be 
advantageous. It also is possible that the upper ther- 
mal limit for successful development of wild embryos 
could be higher than the limit observed in laboratory 
studies. Embryos studied in the laboratory, particularly 
those embryos obtained through in vitro fertilization, 
may perish at high temperatures because of microbial 
infection, which could be inhibited in the wild by the 
presence of natural egg jelly (Staaf et ah, 2011). 
Peak abundances of SD-complex paralarvae ob- 
served in our study were an order of magnitude lower 
than the abundance levels reported during the 1986-87 
El Nino (Vecchione, 1999). This discrepancy could be 
due to chance in sampling or a real difference in abun- 
dance. Among our study years, only in 2006 was an 
El Nino observed, and it was weaker than the one in 
1986-87. The other years of our sampling were either 
in La Nina (1998, 1999, 2000) or neutral (2003) con- 
ditions (http://ggweather.com/enso/oni.htm). Year was 
included in our models as a potential explanatory dis- 
crete variable, but it was determined not to be an infor- 
mative predictor of paralarval abundance or presence, 
indicating no difference between El Nino, La Nina, and 
neutral years. However, the strong positive relation- 
ship between paralarval occurrence and temperature 
found in our study is consistent with Vecchione’s (1999) 
hypothesis that the extraordinarily high paralarval 
abundances in 1987 were related to the 3.5°C increase 
in SST during El Nino. 
Reduced upwelling during the 1986-87 El Nino led 
to a 50% decline in chlorophyll-a in the region of high- 
est paralarval abundance (Vecchione, 1999). Similarly, 
in our study, ommastrephid paralarvae were not as- 
sociated with upwelling zones or their resultant high 
primary productivity. In general, zooplankton biomass 
in the ETP tends to be greatest in the 4 major up- 
welling regions — the Gulf of Tehuantepec, Costa Rica 
Dome, Equatorial Cold Tongue, and coast of Peru (Fer- 
nandez-Alamo and Farber-Lorda, 2006) — but ommas- 
trephid paralarvae were not especially abundant in 
any of these regions (Fig. 2). Indeed, we found no rela- 
tionship between SD-complex paralarvae and primary 
productivity, as measured by CHL or MLD (where the 
thermocline is shallow, primary productivity tends to 
be higher [Pennington et ah, 2006]). 
Species-specific spawning area 
Molecularly identified jumbo squid paralarvae have 
been reported from the Gulf of California (Gilly et 
ah, 2006), off the Baja California Peninsula (Ramos- 
Castillejos et ah, 2010), off Peru (Wakayabashi et ah, 
2008), and now, in this study, from the ETP. We found 
that most molecularly identified paralarvae from the 
ETP were purpleback squid (Fig. 4A), but most adult 
squid captured by jigging were jumbo squid (Fig. 4B). 
Although jigging capture rates may have been biased, 
adult jumbo squid have also been found to outnum- 
ber purpleback squid as prey items of the Dolphinfish 
( Coryphaena hippurus) in the ETP (Olson and Galvan- 
Magana, 2002). Despite this abundance of adult jum- 
bo squid, we found jumbo squid paralarvae in only 2 
samples, and these samples also contained paralarval 
purpleback squid in appreciable numbers (Fig. 4A). 
Neither the geographic locations nor oceanographic 
features of these 2 sampling sites were distinct from 
sites where only purpleback squid was found. There- 
fore, we can say only that purpleback squid paralarvae 
appear to be far more abundant than paralarvae of 
jumbo squid because we have no way of assessing bias 
in the capture rates of the 2 species during plankton 
tows. 
Species-level molecular identification of paralarvae 
was possible in this study only with material from 
oblique tows. If future work on material from surface 
tows were to find a similar predominance of purple- 
back squid, it would support the hypothesis that the 
purpleback squid is the primary ommastrephid that 
spawns in the ETR Although jumbo squid can spawn 
in the ETP or subtropical fringes, its primary spawning 
grounds may actually lie farther to the north, off the 
Baja California Peninsula in both the Pacific (Ramos- 
Catellejos et ah, 2010) and Gulf of California (Staaf 
et ah, 2008; Camarillo-Coop et ah, 2011), and farther 
to the south off Peru (Tafur et ah, 2001; Sakai et ah, 
2008; Anderson and Rodhouse, 2001). 
