82 
Fishery Bulletin 110(1) 
Table 5 
Comparison of diet composition of Scyliorhinus canicula and Squalus blainville in different geographical areas. Values for the 
prey items are values determined with the occurrence index (01) (the percentage of each prey item in all nonempty stomachs), 
except where marked with an asterisk, which are presented as % volume. Superscripts refer to the source study: ^Olaso et al. 
(1998), 2 Serrano et al. (2003), 3 present study, 4 Capape (1974), and 5 Capape (1975). 
Geographical 
location 
S. canicula 
S. blainville 
Atlantic, Bay of 
Biscay (Spain) h* 
Atlantic, Bay of 
Biscay (Spain) 2 - " 
Atlantic 
( Portugal) 3 
Mediterranean 
(Tunisia) 4 
Atlantic 
( Portugal) 3 
Mediterranean 
(Tunisia) 5 
Size range 
Juveniles 
Juveniles 
(total length, cm) 
14.0-70.0 
12.0-68.0 
21.5-61.0 
and adults 
32.6-79.6 
and adults 
Mollusca 
6.7 
3.18 
4.78 
20.9 
26.3 
39.0 
Polychaeta 
4.2 
— 
19.46 
4.9 
3.4 
0.0 
Sipuncula 
0.9 
— 
1.86 
0.0 
1.3 
39.0 
Crustacea 
31.5 
45.61 
66.20 
38.5 
58.8 
32.0 
Echinodermata 
0.0 
0.21 
3.96 
0.0 
0.9 
0.0 
Teleostei 
54.6 
48.20 
32.75 
33.7 
31.9 
72.0 
Others 
0.0 
2.79 
13.17 
2.0 
0.0 
3.0 
Capape (1975) and in the present one, with Sipuncula 
also present in significant amounts in Mediterranean 
waters. For S. canicula , a wider distributional range 
(from the Atlantic Ocean [Bay of Biscay: Olaso et ah, 
1998; Serrano et al., 2003] to the Mediterranean Sea 
[Tunisia: Capape, 1974]) was obtained from the lit- 
erature than that determined for S. blainville. For S. 
canicula, Crustacea and Teleostei were always among 
the most abundant prey items, but with high variability 
in species composition between areas (see Table 5). Poly- 
chaeta and Mollusca were also important in the diet of 
the southernmost populations. As observed previously, 
given the wide range of items that both species prey 
on, their diet may reflect the available fauna at each 
distinct habitat. 
Understanding the feeding ecology of sharks is im- 
portant because changes in diet composition are good 
indicators of changes in fishery-exploited ecosystems. 
In fact, fishing activities such as trawling may induce 
changes in the benthic environment, by modifying the 
abundance of prey items, as well as increasing the 
availability of discards, which may constitute alterna- 
tive food sources for these species (e.g\, Olaso et al., 
1998; 2005; Stevens et al., 2000). In addition, given 
the current rate of global exploitation and mortality of 
sharks (see Herndon et al., 2010 for in-depth details), 
it becomes imperative to identify their main life-histo- 
ry traits in order to design and implement sustainable 
management plans for these species. 
Conclusions 
The present results show that the dietary composition of 
both species in the study area is quite similar: at a broad 
taxonomical level, both species feed mostly on crusta- 
ceans and teleosts, and therefore the potential inver- 
tebrate and fish prey resources are, to a considerable 
extent, partitioned among these important predators. 
Although both species feed on a wide range of prey items, 
changes in crustacean and finfish abundance due to 
trawling activities and an increase in fishing effort and 
fishing depth may introduce changes in predator-prey 
relationships and should be considered when developing 
management plans for sustainable coastal fisheries. Fur- 
ther work should also include continued interseasonal 
and interannual sampling, in order to detect the possible 
influence of fishing activities on benthic organisms and 
on the diet composition of top predators such as elas- 
mobranchs, as well as on other life-history parameters, 
such as age and length structure, age at maturity, and, 
ultimately, stock identification. 
Acknowledgments 
The authors would like to express their gratitude to 
M. Dolbeth and H. Teixeira, who contributed to the 
identification of stomach contents, and also to the three 
reviewers, whose comments and suggestions greatly 
improved the overall quality of the manuscript. We 
thank Rick Brodeur and Julie Schearer (NMFS, NOAA) 
for their constructive reviews of our manuscript. 
Literature cited 
Alonso, M. K., E. A. Crespo, N. A. Garcia, S. N. Pedraza, P. A. 
Mariotti, and N. J. Mora. 
2002. Fishery and ontogenetic driven changes in the diet 
of the spiny dogfish, Squalus acanthias, in Patagonian 
waters, Argentina. Environ. Biol. Fishes 63:193—202. 
