Cordova-Zavaleta et al.: Food habits of Prionace glauca in waters off northern Peru 
311 
84° W 82° W 80° W 78° W 
Map of locations where blue sharks (Prionace glauca) were 
collected in northern Peru between February and December 
2015. The blue vertical gradient defines the position of the 
Peru-Chile Trench (with an average distance from shore of 
130 km or 70 nautical miles). 
the eastern Pacific Ocean. For example, Tricas (1979) 
and Harvey (1989) reported that blue sharks consume 
euphausiids (mostly Thysanoessa spinifera), small fish 
(e.g., the northern anchovy, Engraulis mordax ), and 
a variety of cephalopods (e.g., Loliginidae and Histio- 
teuthidae). Studies from the Mexican Pacific Ocean 
have revealed a high consumption of the pelagic red 
crab (Pleuroncodes planipes ), as well as a variety of 
squid, including Histioteuthis heteropsis, Gonatus cali- 
forniensis, and Ancistrocheirus lesueurii (Markaida and 
Sosa-Nishizaki, 2010; Hernandez-Aguilar et ah, 2016). 
Loor-Andrade et al. (2017) showed that A. lesueurii, 
Stigmatoteuthis hoylei, and the jumbo squid ( Dosidi- 
cus gigas ) were the most consumed species off Ecuador. 
In Chilean waters, prey species included a variety of 
fishes: mackerels ( Trachurus murphyi and the Pacific 
chub mackerel, Scomber japonicus) and tunas ( Thun - 
nus spp.), as well as jumbo squid (Lopez et al., 2010; 
Klarian et al., 2018). 
In Peru, three studies of blue shark diet have re¬ 
vealed that they feed on jumbo squid, Peruvian ancho- 
veta (Engraulis ringens), Pacific sardine ( Sardinops 
sagax), Peruvian hake ( Merluccius gayi peruanus ), 
and eggs from flying fish (Exocoetidae) and Chilean 
silverside (Odontesthes regia ) (Hoyos et al., 1991; 
Elliot et al., 1995, 1996). Although these previous 
studies provide valuable insights into prey species 
of blue sharks off the coast of Peru, their results 
have been limited by sample size, time series, and 
size classes. Therefore, to determine the ecological 
role of blue sharks in the Peruvian marine ecosys¬ 
tem, we focused on providing broader information 
on blue shark food habits off northern Peru by ana¬ 
lyzing stomach contents and assessing diet variabil¬ 
ity by sex, size class, season, and fishing ground. 
Materials and methods 
Sampling and stomach content analysis 
Stomach contents of blue sharks were collected 
between February and December 2015 by onboard 
observers during small-scale driftnet and longline 
fishing trips that landed in Mancora and Sala- 
verry ports in northern Peru (Fig. 1). Sex of each 
shark was determined and total length (TL) was 
measured to the nearest centimeter (Bigelow and 
Schroeder, 1948). Stomachs were extracted and pre¬ 
served in 10% formalin for analysis (Galvan-Maga- 
na et al., 1989). Stomach samples were examined 
at the Laboratorio de Recursos Hidrobiologicos of 
the Universidad Nacional Agraria la Molina, where 
prey items were identified to the lowest possible 
taxon and weighed (wet weight) to the nearest 0.01 
g. Fish items (entire specimens and skeletons) were 
identified according to Chirichigno and Velez (1998) 
and Clothier (1950), and fish otoliths were identi¬ 
fied according to Rivaton and Bourret (1999) and 
Garcfa-Godos (2001). Cephalopods were identified 
by examination of beaks (Wolff, 1982, 1984; Clarke, 
1986; Xavier and Cherel, 2009). Crustaceans and ma¬ 
rine mammals were identified according to Moscoso 
(2013) and Jefferson et al. (2015), respectively. Recon¬ 
struction of cephalopod weights by regression equa¬ 
tions was based on measurements of the lower rostral 
length of cephalopod beaks (Wolff, 1982, 1984; Clarke, 
1986; Smale et al., 1993; Xavier and Cherel, 2009), 
whereas reconstruction of fish weights was based on 
the relationship of length to weight (Fernandez, 1987; 
IMARPE 2 ) and the relationship of otolith radius to to¬ 
tal length (Goicochea and Arrieta, 2008) when possible. 
To assess whether the sample size collected was ap¬ 
propriate to describe the diet of blue sharks, we con¬ 
structed a cumulative prey curve at the family level 
from the total number of prey species identified, ex¬ 
cluding ‘unidentified remains’ (i.e., cephalopod, fish, 
and crustacean) prey items by using the software Es- 
2 IMARPE (Instituto del Mar del Peru). 2012. Crucero 1202- 
04 de “Evaluacion hidroacustica de los recursos pelagicos.” 
Inst. Mar Peru, Inf. Ejec., 49 p. [Available from website.] 
