Martinho et al.: Comparative feeding ecology of two elasmobranch species, Squa/us blainville and Scyliorhmus canicula 
79 
tion of sexual segregation, which to some degree may 
reduce intraspecific competition. In S. acanthias, the 
onset of sexual maturity has been proposed as one 
reason for habitat segregation between sexes, trig- 
gered by changes in energetic needs, feeding habits, 
and consequently, habitat use (Alonso et ah, 2002). 
Seasonal and maturity-stage-related variability 
in the diet of S. canicula 
In this study, both adults and juveniles of S. canicula 
exhibited a common trend in their dietary seasonal 
variations, with Crustacea being the dominant prey 
items, and Teleostei becoming more important as a food 
source during spring and summer months. A similar 
pattern has been observed in the Bay of Biscay (Serrano 
et ah, 2003). 
Compared with juveniles, adults showed a higher 
number of Teleostei in their diet. According to Olaso 
(1998) and Rodriguez-Cabello et al. (2007), as sharks 
grow, the consumption of crustaceans is slightly re- 
duced and teleosts become more important as a food 
source. Although the increase in teleost abundance was 
somewhat small, the present results are in agreement 
with those of previous authors. Rodriguez-Cabello et 
al. (2007) also observed a diet shift from immature to 
mature stages, which can possibly be influenced by the 
onset of maturity, and may be related to changes from 
pelagic to more demersal habitat use (Alonso et ah, 
2002), as well as reduced handling times and higher 
foraging success rates for larger prey (Juanes et al., 
2001) by older and more experienced foragers. This 
higher success rate could indicate that adult sharks 
show some degree of selective feeding, favoring fish 
instead of invertebrates. 
Being a species with a broad spectrum diet, S. canic- 
ula likely takes advantage of available prey, which have 
seasonally abundant cycles. Sousa et al. (2005) observed 
seasonal variations in the composition and abundance of 
demersal assemblages off the Portuguese Atlantic coast, 
which can be linked to upper trophic-level predators, 
such as elasmobranchs. A high abundance of annelid 
worms was observed in the diet of both juveniles and 
adults of this species during the winter, which may 
constitute alternative prey items, given the seasonal 
reduction in crustaceans and teleosts. 
A significant diet overlap was observed throughout 
the year among all four groups: juvenile males, adult 
males, juvenile females, and adult females. This over- 
lap would indicate that both sexes and maturity stages 
share a common habitat. An exception was observed 
in the winter, during which there was no overlap be- 
tween adults and juveniles from both sexes, as well 
as between juvenile and adult males. Such differences 
in prey composition can be attributed to morphologi- 
cal (i.e., mouth gape) and behavioral traits, such as 
habitat segregation (Sims et ah, 2006), differential 
habitat use, and reproductive behavior amongst males 
and females (Sims et ah, 2001; Rodriguez-Cabello et 
al., 2007). 
