Cordova-Zavaleta et al.: Food habits of Prionace glauca in waters off northern Peru 
315 
100 
80 - 
60- 
£ 
c a 
□_ 
o'* 
40 - 
20 - 
I I 
CZ3 
mzi 
Argonauta spp. 
G. antarcticus 
A. lesueurii 
T. rhombus 
J. diaphana 
Exocoetidae eggs 
E. ringens 
D. gigas 
Unidentified fishes 
Unidentified caphalopods 
Other prey 
General Size class II Size class 
Coastal 
Oceanic 
Figure 2 
Prey-specific index of relative importance (%PSIRI) of the overall diet of blue sharks {Prionace glauca) sampled 
in northern Peru between February and December 2015, by size class and longitude of fishing ground. Size 
class II represents fish 150.0-229.9 cm in total length (TL) and size class III represents fish 230.0-309.9 cm 
TL; size class I had only 2 samples and was excluded from most analyses. Two regions were used for analyses 
with longitudes: coastal and oceanic, delineated by the Peru-Chile Trench (which has an average distance 
from shore of 130 km or 70 nautical miles). Taxa include Argonauta spp., Gonatus antarcticus, Ancistrocheirus 
lesueurii, the diamond squid (Thysanoteuthis rhombus), Japetella diaphana, flying fish (Exocoetidae) eggs, the 
Peruvian anchoveta (Engraulis ringens), and the jumbo squid (Dosidicus gigas). 
Table 2 
Levin’s standardized index (Bp, analysis of similarity (ANOSIM), and trophic position (TP) of blue 
sharks {Prionace glauca) from which stomach contents were collected between February and Decem¬ 
ber 2015 off northern Peru, by size class and longitude of fishing ground. Size class II represents 
fish 150.0-229.9 cm in total length (TL) and size class III represents fish 230.0-309.9 cm TL; size 
class I had only 2 samples and was excluded from most analyses. Two regions, coastal and oce¬ 
anic, were used for the analyses with longitudes of fishing grounds: these regions are separated 
by the Peru-Chile Trench (which has an average distance from shore of 130 km or 70 nautical 
miles). General=overall analysis. 
Factor 
Subfactor 
ANOSIM 
Bi 
TP 
General 
- 
- 
0.26 
4.4 
Size class 
II 
II vs III CR=0.05; 
0.19 
4.4 
III 
P<0.05*) 
0.42 
4.4 
Fishing ground longitude 
Coastal 
Coastal vs. oceanic 
0.18 
4.4 
Oceanic 
(7?=0.10; P<0.01*) 
0.40 
4.4 
The niche breadth of the blue shark was considered 
narrow according to Levin’s standardized index (Table 
2), indicating a higher degree of specialization. The 
graphical analysis suggests a similar feeding pattern, 
with a clear dominance of the Argonautidae family 
(Fig. 3). Additionally, the trophic position of the blue 
shark was calculated as 4.4, indicating that the blue 
shark is a high trophic-level consumer within the food 
web off northern Peru. 
Size class groups were evaluated at 20- and 30-cm- 
TL intervals and showed no clear organization of size 
classes. Nevertheless, cluster analysis with a 40-cm- 
TL interval showed positive results, with 3 size classes 
identified at 50% of Bray-Curtis dissimilarity (Fig. 4). 
