Clarke et al.: Elasmobranch bycatch from the shrimp trawl fishery along the Pacific coast of Costa Rica 
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Figure 4 
Proportion of females caught at 3 depth ranges, (A) <50 m, (C) 50-100 m, and (El 
>100 m, and proportion of immature individuals caught at depth of (B) <50 m, (D) 
50-100 m, and (F) >100 m for 11 elasmobranch species sampled along the Pacific coast 
of Costa Rica during 2010-2012. The following species abbreviations are used: MHE 
(brown smoothhound [ Mustelus henlei]), MLU (sicklefin smoothhound [Mustelus lunula- 
fas]), UAS (Panamic stingray [Urotrygon aspidura]), UCH (blotched stingray [Urotry- 
gon chilensis]), URO (thorny stingray [ Urotrygon rogersi]), RVE (rasptail skate [Raja 
velezi]), ZXY (witch guitarfish [Zapteryx xyster]), DOM (bullseye electric ray [ Diplobatis 
ommata]), NEN (giant electric ray [Nareine entemedor]), NVE (vermiculate electric ray 
[Narcine venniculatus]), and TPE (Peruvian torpedo [Torpedo peruviana ] ). 
ages in the water column during the night (Lowe et 
al., 1994). If feeding habits of the Peruvian torpedo are 
similar to those of the Pacific electric ray, they would 
explain the higher catch rates for this species observed 
during the daytime. 
Elasmobranch distribution patterns varied intraspe- 
cifically, according to sex and size. Sexual segregation 
has been documented widely in elasmobranchs (Wear- 
mouth and Sims, 2008) and tends to occur more often 
in adult populations, although it is not restricted to 
them (Carlisle et al., 2007; Wearmouth and Sims, 2008). 
Our study showed that small ray species, such as the 
Panamic stingray and thorny stingray, formed large 
aggregations dominated by mature females in shallow 
waters. In the case of these small rays, sexual segrega- 
tion in shallow waters may reduce intraspecific compe- 
tition for food resources (Carlisle et ah, 2007; Espinoza 
et ah, 2012). In contrast, some species like the brown 
smoothhound had a male-biased sex ratio; male brown 
smoothhound occurred in deep habitats (depths >100 
m) and gravid females were more abundant in warmer 
(>20°C), shallow, coastal habitats. Gravid females are 
thought to use warmer habitats that may offer ther- 
mal reproductive advantages, such as increased growth 
rates of embryos (Hight and Lowe, 2007; Pereyra et al., 
2008; Speed et al., 2012). 
Elasmobranch assemblages 
The elasmobranch assemblages were characterized 
by the presence of 5 dominant species (i.e., rasptail 
skate, Panamic stingray, brown smoothhound, witch 
guitarfish, and Peruvian torpedo), a group that ac- 
counted for more than 75% of the total abundance of 
