452 
Fishery Bulletin 11 5(4) 
82'30' 81*40' 80" 50' 80*00' 79*10' 78‘20'W 
4* 10' 
5* 00' 
5* 50' 
6* 40' 
7* 30' 
8* 20' S 
Figure 1 
Map of the study area and the 7 landing sites where smooth 
hammerhead (Sphyrna zygaena) were collected off northern Peru 
from December 2012 through June 2015. The black line defines 
the division between the Tropical East Pacific Marine Province 
(TEP-MP) and the Warm Temperate Southeastern Pacific Marine 
Province (WTSP-MP), ra=number of stomachs collected from each 
marine province. This map was created with Seaturtle.org Map- 
tool (Seaturtle.org Inc. website, accessed January 2017). 
al., 2016). However, the fisheries lack robust 
monitoring and management, and species bi¬ 
ology and ecology remain poorly understood, 
both locally and worldwide (Fowler et al., 
2005; Cortes et al., 2010). 
There are limited studies from Mexico, 
Ecuador, and Peru on the diet of smooth 
hammerhead in the Pacific Ocean. Research 
shows that the diet of this shark in waters 
off Mexico is composed of fishes and eephalo- 
pods (eg , California needlefish [Strongylura 
exilis]; common clubhook squid [ Onychoteu- 
this hanksia ]) (Galvan-Magana et al., 1989; 
Ochoa-Dlaz, 2009; Galvan-Magana et al., 
2013). In waters off Ecuador, information 
suggests that the diet is composed mainly of 
cephalopods (e.g., jumbo flying squid [Dosidi- 
cus gigas ]; purpleback flying squid [Stheno- 
teuthis oualaniensis ]; whip-lash squid [Mas- 
tigoteuthis dentata ]; and sharpear enope 
squid [ Ancistrocheirus lesueurii ]) (Castane¬ 
da and Sandoval, 2004; Estupinan-Montaho 
and Cedeno-Figueroa, 2005; Bolano Mar¬ 
tinez, 2009). In one study in Peru, the diet 
of smooth hammerhead was analyzed and 
smooth hammerheads were found to feed pri¬ 
marily on fishes (Pacific sardine [Sardinops 
sagax ]; Peruvian hake [Merluccius gayi pe- 
ruanus ]; and Peruvian anchoveta [Engraulis 
ringens ]), as well as on cephalopods (. Loligo 
spp., and jumbo squids) (Castaneda 1 ). Al¬ 
though this study in Peru had an adequate 
sample size, time series, and size distribu¬ 
tion for the smooth hammerhead, it is more 
descriptive than analytical and is limited to 
a seasonal comparison. 
We sought to better understand the trophic ecology 
of smooth hammerhead off the coast of northern Peru 
by analyzing stomach contents. We assessed diet vari¬ 
ability by sex, body size, location, season, year, and en¬ 
vironmental conditions. 
Materials and methods 
Collections, storage, and analysis of samples 
Samples were collected from a small-scale driftnet fish¬ 
ery from December 2012 through June 2015 at 7 land¬ 
ing sites along the coast of northern Peru: Zorritos, 
Acapulco, Cancas, Mancora, Yacila, San Jose, and Sa- 
laverry (Fig. 1). Nets in this fishery are typically set at 
the time of sunset and retrieved the following morning 
for an average set length of ca. 14 h (Alfaro-Shigueto 
et al., 2010). Sharks were measured (total length) and 
sex was determined. Stomachs were extracted and pre¬ 
served in 10% formalin solution. 
1 Castaneda, J. 2001. Biologia y pesqueria del “tiburon mar- 
tillo” (Sphyrna zygaena) en Lambayeque, 1991-2000. Inst. 
Mar Peru Inf. Prog. 139:17-32. [Available from website.] 
Analysis of stomach contents 
Prey items from stomach contents were analyzed at the 
Laboratorio de Ecologla Trofica of the Institute de Mar 
del Peru, 2 and identified to the lowest possible taxon, 
counted, and weighed (wet weight). For identification 
of fishes and cephalopods, and their hard parts (oto¬ 
liths and beaks), the following identification guides 
were used: Iverson and Pinkas (1971); Wolff (1982, 
1984); Clarke (1986); Chirichigno and Cornejo (2001); 
Garcia-Godos (2001); Lu and Ickeringill (2002); and 
Xavier and Cherel (2009). Cephalopod beaks were used 
to reconstruct total mass at ingestion, by using regres¬ 
sion equations (Lu and Ickeringill, 2002). Values for 
stage of digestion were allocated to each prey item and 
ranged from 1 (little or no digestion) to 4 (advanced 
state of digestion) (Bolano Martinez, 2009). 
Diet was quantified by using percentage of prey, by 
number (%N), weight (%W), and frequency of occurrence 
(%0) (Hyslop, 1980). The index of relative importance 
(IRI) was calculated as IRI=%0 (%N + %W). It was 
then divided by the total IRI for all items to express the 
2 and at the Laboratorio de Biologia Marina of the Universi- 
dad Cientifica del Sur. 
