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Fishery Bulletin 11 1 (1) 
only if the station was located within 18.5 km (10 nau- 
tical miles) and was sampled within 12 h of the net 
tow. SST and SSS were averaged over a 2-h window 
centered on the time of the net tow. In total, 137 bongo 
and 164 manta samples were discarded according to 
these criteria, leaving 517 bongo and 620 manta sam- 
ples. Many of the discards (56 bongo and 57 manta) 
were collected aboard the McArthur in 2003, when the 
thermosalinograph malfunctioned. Three outlier points 
were also removed: an abnormally low value for each of 
CHL and SST, and an abnormally high value for MLD. 
Relationships between ommastrephid abundance 
and oceanographic variables were explored with gener- 
alized linear models in the R statistics package, vers. 
2.1.1 (R Development Core Team, 2005). We used gen- 
eralized linear models because of their utility in model- 
ing relationships between cetaceans and oceanographic 
habitat (Redfern et ah, 2006) and between cephalopod 
paralarvae and oceanographic habitat off western Ibe- 
ria (Moreno et al., 2009). Typical of marine survey 
counts, our paralarval abundance data were overdis- 
persed, with a high proportion of zeros and a few very 
large samples. Therefore, we followed Aitchison (1955) 
and Pennington (1983) in performance of a 2-step anal- 
ysis, in which we separated the data into a binomial 
presence and absence data set (hereafter referred to as 
paralarval presence ) and an abundance data set that 
included only stations at which paralarvae were pres- 
ent (hereafter referred to as paralarval abundance). To 
analyze paralarval presence, we used a binomial distri- 
bution with a logit link; for paralarval abundance we 
used a lognormal distribution. We used an automated 
forward/backward stepwise approach based on Akaike’s 
information criterion (AIC) to select the variables for 
inclusion in the model. 
Results 
Abundance of paralarvae 
Paralarvae of the SD complex were found in 781 of the 
1438 formalin-preserved plankton samples. By type of 
tow, 355 of 656 oblique bongo tows (54.28%) and 426 
of 784 surface manta tows (54.34%) contained SD-com- 
plex paralarvae. The greatest abundance in a single 
manta tow was 1588 paralarvae versus 64 paralarvae 
in a single bongo tow. SD-complex paralarvae taken in 
bongo tows were distributed over a somewhat broader 
geographical area than were those paralarvae captured 
in manta tows (Fig. 2), but density of captured paralar- 
vae was typically at least an order of magnitude great- 
er in manta tows. 
Size of paralarvae 
Average mantle length in manta tows was 1.94 ±1.29 
mm fn=779; range 0.7-15 mm ML) versus 1.86 ±1.0 
mm (ra = 148; range 0.6—7 mm ML) in bongo tows. No 
significant difference was found between these distri- 
butions (1-way analysis of variance [ANOVA], P= 0.44). 
Relationship of presence and abundance of paralarvae to 
environmental variables and modeling 
The stepwise approach for the presence models select- 
ed SST, SSS, and TT as predictor variables for manta 
data, and SST and MLD for bongo data (Table 1). The 
decrease in the AIC values for these models and the 
increase in the percentage of explained deviance came 
primarily from SST for both bongo and manta tows, 
with minimal contribution from MLD, SSS, and TT. 
Therefore, SST emerged as the strongest predictor for 
presence of SD-complex paralarvae, and the probability 
of capture increased monotonically as SST increased 
from 15°C to 32°C (Fig. 3). 
Analysis of paralarval abundance, rather than pres- 
ence, revealed no strong predictors (Table 2). For bongo 
tows, the stepwise approach selected CHL, TT, and SST 
in the final model (7.5% explained deviance). For manta 
tows, CHL, SST, MLD, and TT were all selected (12.1% 
explained deviance). There appears to be little relation- 
ship between these variables and nonzero paralarval 
abundance, which varied over a wide range of each en- 
vironmental variable for both manta and bongo tows. 
Species identification 
In total, 97 SD-complex paralarvae were found in 12 
of the 38 ethanol-preserved samples. Of these paralar- 
vae, 81 were identified genetically as Sthenoteuthis 
oualaniensis and 16 as Dosidicus gigas. Paralarvae of 
purpleback squid were found over a much greater area 
than paralarvae of jumbo squid (Fig. 4A). Eight om- 
mastrephid paralarvae were removed from the 2 frozen 
samples and identified genetically as purpleback squid. 
Non-ommastrephid cephalopods were identified in 
many of the tows, most commonly as taxa in the teu- 
thid families Enoploteuthidae, Onychoteuthidae, Gona- 
tidae, Chtenopterygidae, Cranchiidae, and Brachioteu- 
thidae and in the octopod genera Argonauta and Tre- 
moctopus; all have previously been reported from the 
ETP (Ueyanagi and Nonaka, 1993; Vecchione, 1999). 
Of the 129 adult squid captured in jigging sessions, 
118 were jumbo squid and 11 were purpleback squid. 
Jumbo squid adults were found primarily in the south- 
ernmost sampling sites off Peru, but the few purple- 
back squid adults were more evenly distributed (Fig. 
4B). 
Discussion 
This study represents the most extensive sampling to 
date in the ETP of paralarvae of jumbo squid and pur- 
pleback squid, covering most of their broad equatorial 
and subtropical region of range overlap in the Pacific 
during a period of 8 years. 
