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Fishery Bulletin 107(1) 
Morphological features used for measuring dorsal mantle length (DML), total length 
(TL), and maximum length (L Max ) of squid. 
and anterior tips of the dorsal side of the mantle, total 
length was measured as the distance between the pos- 
terior tip of the mantle to the end of the longest arm, 
and maximum length was measured as the distance 
between the posterior tip of the mantle to the end of 
the longest tentacle (Fig. 1). Beaks were extracted from 
the buccal mass and the lower rostrum length (LRL) of 
the lower beak was measured to the nearest 0.01 mil- 
limeter. Lower beaks were held so that the rostrum tip 
was facing the observer and then turned to a left-facing 
orientation (Fig. 2); the lower beak was best viewed 
when held against a white background for contrast. The 
LRL of L. pealeii was measured by placing the tip of the 
moving arm of the calipers inside the jaw angle of the 
lower beak and extending it to the tip of the rostrum 
(Clarke, 1986) (Fig. 2A). The LRL of I. illecebrosus 
was measured from the tip of the rostrum to the jaw 
angle. In I. illecebrosus the shoulder forms a tooth which 
facilitates location of the jaw angle (Fig. 2B). Beaks from 
both species were measured either under a dissecting 
microscope or a magnifying glass. 
Least squares regression analysis was used to esti- 
mate the relationship between mantle length and total 
length, mantle length and maximum length, and LRL 
and mantle length for both squid species. Using the 
PROC UNIVARIATE command in SAS, vers. 9.1 (SAS 
Institute Inc., Cary, NC), we found that all variables 
were in compliance with assumptions of normality and 
no outliers were detected. Linear models were used to 
develop predictive equations for all pairings of morpho- 
logical structures. All statistical analyses were per- 
formed by using the PROC REG command in SAS. 
Results 
Total length (TL) and maximum length (L Max ) were 
strongly related to dorsal mantle length (DML) in both 
L. pealeii and 7. illecebrosus. The r 2 values for all body 
size relationships ranged from 0.88 to 0.98 and were 
highly significant (P<0.0001) (Table 1). A total of 434 L. 
pealeii ranging in size from 1.9 to 28.0 cm (DML) and 
158 7. illecebrosus ranging in size from 4.4 to 28.4 cm 
(DML) were measured to develop allometric relationships 
between DML, TL, and L Max . 
Equations for reconstructing original squid size 
(DML) from lower rostrum lengths (LRL) were highly 
significant (PcO.0001) in both L. pealeii and 7. illece- 
brosus (Table 1). The model developed for L. pealeii 
improved the only known equation for this species by 
expanding the sample size from n- 25 and the coeffi- 
cient of determination (r 2 ) of 0.73 (Gannon et al., 1997) 
to rc = 144 and an r 2 of 0.83 (Table 1). Lower rostrum 
lengths (LRL) were measured from L. pealeii rang- 
ing from 2.6 to 24.7 cm (DML). The predictive model 
for estimating DML from LRL in 7. illecebrosus was 
developed from 89 specimens ranging from 4.4 to 28.4 
cm (DML). The relationship between LRL and DML in 
7. illecebrosus was stronger and less variable (r 2 = 0.94, 
coefficient of variation [CV] = 8.15) in comparison to L. 
pealeii (r 2 =0.83, CV=15.94). Measurement of the lower 
rostral length in 7. illecebrosus is greatly facilitated by 
the presence of a tooth located in the angle point. This 
structure is absent in the lower beak of L. pealeii, and 
may make measuring beaks from this species more dif- 
ficult and prone to error. 
Discussion 
The results of the present study are intended to assist 
and encourage quantitative assessments of cephalo- 
pod prey in the diets of a broad range of finfish, elas- 
mobranch, marine mammal, and seabird predators. 
Although methods for identification and reconstruc- 
tion of original body size from cephalopod beaks have 
