Martinho et al.: Comparative feeding ecology of two elasmobranch species, Squalus blainville and Scyhorhinus canicula 
77 
100 
01 (%) 
100 
100 
B 
Ol (%) 
80 
100 
Figure 4 
Relative importance of each prey category for (A) Scyliorhinus 
canicula and (Bi Squalus blainville determined by using the 
combined values of the percent number (numerical index, NI), 
percent weight (gravimetric index, GI), and frequency of occur- 
rence (occurrence index, OI). Each tick mark along the OI axis 
represents 10%. 
when no diet overlap was observed, occurred 
during the winter between juvenile and adult 
males, adult females and juvenile males, and 
adult females and juvenile males. 
Discussion 
A comparison of the generic diet of 5. canicula 
and S. blainville 
The S. canicula specimens captured in 2006 
had a broad diet spectrum, which is in agree- 
ment with several published studies of this 
species (Ellis et ah, 1996; Olaso, 1998; Serrano 
et al., 2003; Domi et al., 2005; Olaso et al., 
2005). In the present study, the main dietary 
items of S. canicula were Crustacea, Teleostei, 
and Mollusca (essentially cephalopods), with 
Polychaeta also as an important food item 
but in lower magnitude. The most abundant 
crustaceans belonged to the order Decapoda, 
which were the dominant prey items in the 
diet of this species in number, occurrence, and 
weight. Within this group, the benthic crabs 
Pagurus spp. and Goneplax rhomboides were 
the most abundant species, indicating the abil- 
ity of S. canicula to forage in benthic habitats. 
Effectively, this species has been described as 
an active benthic feeder that uses a range of 
active senses for finding prey (e.g., Olaso et al., 
2005; Kimber et al., 2009). In the Bay of Biscay, 
high prey diversity enabled its classification 
as a generalist feeding species (Serrano et al., 
2003). This species has also been considered 
an opportunistic scavenger (Olaso et al., 1998; 
2005), taking advantage of the discards from 
local trawling fisheries. 
The presence of pelagic fish such as Sardina 
pilchardus, Trachurus trachurus, and Scomber 
scombrus in the stomach contents of S. canic- 
ula is also evidence of this species as a pelagic 
predator. These and other pelagic fish species 
have also been reported to be an important 
part of the diet of S. canicula captured off the 
Cantabrian coast of Spain (see Olaso et al., 
2005). The presence of Chondrichthyes (apart 
from Rajidae) in the diet of S. canicula may, up to 
some point, indicate the possibility of cannibalism, as 
observed in other areas of the Atlantic (Olaso et al., 
2005). 
For S. blainville, as stated previously, information 
on its diet composition is limited to that supplied by 
Capape (1975), who classified it as a voracious species. 
In the present study, the major prey groups of S. blain- 
ville were Crustacea (mainly Paguridae and Portunidae 
decapods), Teleostei (Soleidae), and to a lesser extent, 
Mollusca (mostly Cephalopoda), all of which (except Te- 
leostei) denote the ability of this species to forage near 
the seabed, targeting preferentially benthic prey. In the 
Mediterranean, Teleostei were the most ubiquitous prey 
items in S. blainville, and there was a lower, but simi- 
lar, occurrence of Mollusca, Sipuncula, and Crustacea 
(see Capape, 1975). The differences in diet composition 
may be attributed to distinct foraging areas, food avail- 
ability, and depth that characterize the Mediterranean 
and Atlantic habitats. Ultimately, the diet composition 
of S. blainville likely reflects the availability of prey 
items in the environment. A congener species, Squalus 
acanthias, captured off Patagonian waters, Argentina, 
was determined to be a fairly indiscriminate predator 
(Alonso et al., 2002) as was S. blainville in our study. 
As with S. canicula, the compiled indices also revealed 
