NOTE Staudinger et al.: Reconstruction of original body size and allometric relationships for Loligo pealen and ///ex illecebrosus 
103 
A 
Rostrum tip 
Jaw angle 
B 
Rostrum tip 
LRL 
Tooth 
Shoulder 
Figure 2 
Jaw angle 
Orientation and key morphological structures of the lower beak of (A) the longfin inshore ( Loligo pealeii ) and < B ) the 
northern shortfin (///ex illecebrosus) squids. Lower rostrum length (LRL) is measured from the tip of the rostrum to the 
jaw angle. 
Table 1 
Least squares regression equations for describing the relationship of total length (TL) to dorsal mantle length (DML) and maxi- 
mum length (L Max ), and the relation of DML to the lower rostral length of the lower beak (LRL) in longfin inshore ( Loligo pealeii) 
and northern shortfin (///ex illecebrosus) squids. All measurements are given in centimeters. «=sample size, r 2 =coefficient of 
determination, T’=the /’-statistic, and / > -value= significance of each model. 
Species 
Equation 
n 
,.2 
F 
P-value 
Loligo pealeii 
TL = 1.29 DML + 3.11 
434 
0.97 
14,818.7 
<0.0001 
L Max = 1.52DML + 6.17 
434 
0.88 
3018.05 
<0.0001 
DML = 92.29LRL - 2.12 
144 
0.83 
639.2 
<0.0001 
Illex illecebrosus 
TL = 1.16DML -1.43 
158 
0.98 
6624.16 
<0.0001 
L Max = 2.05DML-0.44 
158 
0.97 
4409.64 
<0.0001 
DML = 48.92 LRL + 0.82 
89 
0.94 
1364.18 
<0.0001 
been available for several decades (Clarke, 1980, 1986), 
information on body-size relationships in the two most 
common species of squid found in the Northwest Atlan- 
tic Ocean has been lacking. Results presented here 
improved the fit of the only known model for reconstruct- 
ing mantle length from the rostral length of the lower 
beak in L. pealeii. Clarke (1986) provided an equation 
for reconstructing body mass from the LRL in 7. illece- 
brosus ; however, to the best of our knowledge, an equa- 
tion for reconstructing body length was not previously 
available for this species. 
Mantle length is the universally measured character- 
istic to assess squid size in population and commercial 
surveys because it is easy to measure and exhibits 
less variation in comparison to other structures. We 
do not advocate changing the current method because, 
as shown here, morphological relationships for total 
length (TL) and maximum length (L Max ) can be reliably 
predicted from dorsal mantle length (DML). However, 
for the purposes of evaluating relative predator-prey 
body-size relationships, mantle length does not accu- 
rately represent total size. Squid swim with their arms 
extended in front of them or bent slightly downwards 
and rarely extend their two tentacles, which are longer 
than their eight arms, except during feeding and mat- 
ing (Hanlon and Messenger, 1996). Therefore, when 
a predator attacks a squid it likely perceives the to- 
tal body size of the squid as the sum of the arms and 
mantle, thus, making TL the appropriate measure for 
calculating relative body size. In response to predator 
