Mendez-Macias et al.: Trophic ecology and ontogenetic shift in the diet of Mustelus lunulatus in the southeastern Pacific Ocean 
253 
Figure 6 
Nonmetric multidimensional scaling (MDS) ordination indicating the changes 
in diet of sicklefin smoothhounds (Mustelus lunulatus) caught in the south¬ 
eastern Pacific Ocean between November 2003 and October 2004, for (A) 
maturity stages (juvenile and adult) and (B) size classes. The size classes are 
60-90 cm in total length (TL, Size I), 90-120 cm TL (Size II), and 120-150 cm 
TL (Size III). 
prey such as the small arched box crab, present at depths 
of 1-300 m (Hendrickx, 1997), and Acantliocarpus desolari, 
present at depths of 100-300 m (Del Rosario and Abele, 
1976). These species typically inhabit seabeds formed from 
sand, mud, pebbles, stones, or dead coral (Hendrickx, 1997; 
Del Rosario and Abele, 1976). 
Moreno-Sanchez et al. (2012) mentioned that juvenile 
and adult sicklefin smoothhounds fed on the same prey, 
but adults had a stronger preference for fish species. 
However, the authors analyzed juveniles and adults of 
both sexes combined, which may have obscured dietary 
patterns. In our study, for which the sexes were analyzed 
separately, both female and male juveniles were found to 
have a diet based on Achelous iridescens (>30% PSIRI; 
Fig. 3), a crustacean inhabiting sandy and muddy bottoms 
(Wehrtmann and Cortes, 2009) that can be easily captured 
by young sharks that are still developing their hunting 
skills. Adults (both female and male) ate less of this crus¬ 
tacean and complemented their diet with cephalopods 
(in the case of females) as well as other 
crustacean species (in the case of males). 
These results indicate that adult sharks, 
with their larger size and better hunting 
skills, explore new areas (i.e., the pelagic 
zone) while they search for food. The con¬ 
sumption of different foods by sharks at 
different stages of sexual maturity may 
be associated with 1) different energy 
requirements, 2) reproductive processes, 
3) cost-benefit tradeoffs, 4) prey avail¬ 
ability, and 5) hunting skills. 
To date, no trophic study of the sick¬ 
lefin smoothhound had analyzed feeding 
patterns throughout the year. Therefore, 
this study is the first to have conducted 
an analysis that took into account the 
trophic spectrum of the sicklefin smooth- 
hound in 4 trimesters. The results of our 
study indicate that this species prefers A. 
iridescens throughout the year. However, 
between November 2003 and January 
2004 the prey consumed was dominated 
by crustaceans (PSIRI: 69.7%), and in 
the other 3 trimesters the presence of 
A. iridescens increased in importance by 
45-65% (PSIRI) and there was a corre¬ 
sponding reduction in the presence of 
crustaceans (Fig. 5). 
These results are consistent with the 
abundance of crustaceans estimated by 
Mora et al. (2010), who identified 150 
species of macroinvertebrates (120 crus¬ 
taceans, 15 mollusks, 13 echinoderms, 
and 2 cnidarians), with the most abun¬ 
dant species being a swimming crab, 
A. iridescens, followed by a cephalopod, 
the dart squid. These observations sup¬ 
port our results that indicate that the 
sicklefin smoothhound is a species that 
specializes in the consumption of crustaceans that are 
highly abundant in the zone they inhabit. Because of the 
substantial presence of crustaceans in stomachs of spec¬ 
imens during November-January (Trimester I) and the 
greater number of individuals in Size I (n=95) analyzed in 
the study period, we hypothesize that during this period 
juvenile individuals consume more small crustaceans that 
are easier to hunt and digest. Nonetheless, more studies 
are required, including research related 1) to abundance of 
prey species and (2) to other biological aspects of the sick¬ 
lefin smoothhound (such as reproduction and growth) that 
would improve understanding of the spatial and temporal 
feeding behavior of this species. 
The study of the diet of sicklefin smoothhounds by 
Moreno-Sanchez et al. (2012) may be the most detailed so 
far, and it found no ontogenetic changes in the diet of this 
species. Our study, in contrast, has revealed that the diet 
of sicklefin smoothhounds changes as they grow (Fig. 4) 
and become sexually mature (Fig. 3), from a diet composed 
