Gonzalez-Pestana et al.: Trophic ecology of Sphyrna zygaena off northern Peru 
455 
Table 2 
Trophic niche width of 2 groups of taxa in the diet of 
smooth hammerhead (Sphyrna zygaena) collected from 
December 2012 through June 2015 in northern Peru, 
according to Levin and Berge-Parker indices. The Berg- 
er-Parker index uses this formula: d=(n j max)/N, where 
Af=the number of all recorded food components and 
max=the number of specimens with the most numerous 
taxon in the diet. 
Berger-Parker index 
Levin index 
d 
1/N 
Cephalopods 
0.24 
0.31 
0.0102 
Fish species 
0.30 
0.39 
0.0005 
Total 
0.27 
0.38 
0.0005 
classes that presented a significant difference, size 
classes I—III had the highest /^-statistic and the lowest 
overlap, and therefore their diets are well separated. 
Size classes II and III had the lowest /^-statistic and 
the highest overlap; therefore their diets were mini¬ 
mally separated (Table 3). 
According to analysis with SIMPER, the prey spe¬ 
cies that most contributed to the diet in size class I 
are M. dentata, teleosts and the Patagonian squid; in 
size class II they were the Patagonian squid, the jumbo 
flying squid, and M. dentata ; in size class III they were 
the jumbo flying squid and Patagonian squid; and in 
size class IV they were the jumbo flying squid, sharp- 
ear enope squid, Gonatus antarcticus, and giant squid 
(Architeuthis dux ) in order of importance. 
The IRI showed a similar trend. Sharks 
in size class I fed chiefly on Patagonian 
squid (31% of HR), teleosts (26%) and 
whip-lash squid (25%); whereas sharks 
in size class II fed chiefly on Patagonian 
squid (49%), whip-lash squid (13%) and 
jumbo squid (13%); sharks in size class 
III fed chiefly on jumbo flying squid (54%) 
and Patagonian squid (24%); and sharks 
in size class IV fed chiefly on jumbo fly¬ 
ing squid (62%), giant squid (15%) and 
sharpear enope squid (9%) (Fig. 2). 
We were also able to identify some 
general trends in the diet as sharks in¬ 
creased in size, such as, a reduction in 
the consumption of teleosts and whip¬ 
lash squid and an increase in the con¬ 
sumption of jumbo flying squid and shar¬ 
pear enope squid. The giant squid was 
present only in the diets of sharks in size 
class IV (Fig. 3). Sharks in size classes 
II and III were the most specialized 
feeders, whereas sharks in size class I 
were the least specialized. Sharks in size 
class II (mean trophic position: 4.34 cm 
TL) had the lowest trophic position, and 
sharks in size class IV had the highest trophic posi¬ 
tion (mean trophic position: 4.63 cm TL). As an overall 
trend, sharks increased their trophic position as they 
increased in size. 
Of all the other factors assessed (sex, location, sea¬ 
son, year, and environmental conditions), ANOSIM 
showed that the dietary composition of smooth ham¬ 
merhead differed significantly only between location 
and year. However, these differences were small (R- 
statistic<0.25, P<0.05) and an overlap exists between 
the dietary composition of these factors (Clarke, 1993). 
We therefore concluded that the diet of smooth ham¬ 
merhead did not show variability according to the sex, 
location, season, year, or environmental conditions. 
Discussion 
Our analyses indicate that the smooth hammerhead 
has a narrow trophic niche width and a high trophic 
position and can therefore be considered a specialized 
top predator. These results complement the findings 
from other diet studies of smooth hammerhead in the 
eastern Pacific Ocean (Ecuador and Baja California) 
and southeastern Africa—studies in which this shark 
species was found to feed mainly on cephalopods (e.g., 
jumbo squid, Patagonian squid, whip-lash squid, and 
sharpear enope squid) (Smale, 1991; Smale and Cliff, 
1998; Castaneda and Sandoval, 2004; Estupinan-Mon- 
tano and Cedeno-Figueroa, 2005; Galvan-Magana et 
al., 2013). Studies from Ecuador and Baja California 
showed that the smooth hammerhead is a special¬ 
ist predator with a trophic level between 4 and 4.5, 
140 
1 2 3 4 5 6 7 8 
Number of prey species 
Figure 2 
Number of prey species in stomachs of smooth hammerhead (Sphyrna 
zygaena). Smooth hammerheads were collected off northern Peru from 
December 2012 through June 2015. 
