Clarke et at; Elasmobranch bycatch from the shrimp trawl fishery along the Pacific coast of Costa Rica 
13 
RDA 1 (14.2%) RDA 1 (7.6%) 
Figure 6 
Redundancy analysis between environmental variables and elasmobranch abundance (measured as catch per unit of effort 
[CPUE]) along the Pacific coast of Costa Rica. Dependent variables were CPUE of species caught (A) in deepwater surveys 
(2008-2011); (B) in monitoring surveys in the central Pacific region (2010-2012); and (C) in commercial surveys in the 
central Pacific region (2010-2012). Environmental variables were depth, latitude, year, season (rainy, dry), and diel period. 
Circles represent categorical variables, and arrows represent continuous variables. The values given in parentheses on 
the axes are the percentages of variation in the total species-environmental data represented in the biplots. The length of 
the vector arrow indicates the strength of the correlation, and its direction indicates the relationship with a species. The 
following species abbreviations are used: MHE (brown smoothhound [ Mustelus henlei ]), RVE (rasptail skate [ Raja velezi]), 
TPE (Peruvian torpedo [Torpedo peruviana ]), ZXY (witch guitarfish [Zapteryx xyster]), SCA (Pacific angel shark [ Squatina 
californica]), MLU (sicklefin smoothhound [Mustelus lunulatus ]), RST (golden cownose ray [Rhinoptera steindachneri]), 
RLE (whitesnout guitarfish [Rhinobatos leucorhynchus]), NEN (giant electric ray [ Narcine entemedor ]), DOM (bullseye 
electric ray [ Diplobatis ommata ]), REQ (equatorial skate [ Raja equatorialis ]), DLO (longtail stingray [ Dasyatis longa ]), NVE 
(vermiculate electric ray [ Narcine vermiculatus]), URO (thorny stingray [Urotrygon rogersi ]), and UAS (Panamic stingray 
[Urotrygon aspidura]). 
elasmobranchs in this study. Similar observations have 
been documented for other tropical shrimp fisheries in 
Costa Rica (Campos, 1986), Australia (Stobutzki et al., 
2001), and Mexico (Lopez-Martmez et al., 2010). Elas- 
mobranch bycatch from bottom-trawl fisheries is as- 
sumed to reflect the composition of demersal species; 
however, it is important to consider that trawling gear 
is designed for soft and sandy bottoms. Therefore, spe- 
cies that use reef or hardbottom habitats are likely to 
be underrepresented in bottom-trawl fisheries (Lopez- 
Martmez et al., 2010). Similarly, fast-swimming or pe- 
lagic elasmobranchs (e.g., spotted eagle ray [Aetobatus 
laticeps ], golden cownose ray, and scalloped hammer- 
head [Sphyrna lewini]) are less likely to be caught by 
bottom trawls. 
The assemblage of shallow-water elasmobranchs 
(depths <50 m) comprised 22 species, among which 
the Panamic stingray was the most abundant. High 
abundances of small rays also have been reported 
for shallow-water bycatch in Colombia (Mejia-Falla 
and Navia 1 ) and the Gulf of California (Rabago- 
Quiroz et al., 2011). In our study, patchy distribu- 
tions and large aggregations were observed for many 
small round stingrays (Urotrygon spp.) and electric 
rays ( Narcine spp.), possibly as a result of high food 
availability (Vianna and Vooren, 2009; Knip et al., 
2010) or reproductive behavior (Vianna and Vooren, 
2009). 
Elasmobranch bycatch associated with the shrimp 
fishery in Costa Rica was first described by Campos 
(1986). Differences in sampling methods, however, pre- 
vent direct comparisons with our study. For example, 
we examined the total catch of elasmobranchs, but 
Campos (1986) analyzed only a small subsample of that 
catch in 1983-1984. Moreover, Campos (1986) surveyed 
a smaller depth range (<100 m), and reported only 9 
batoids (skates and rays), 4 sharks, and 4 unidentified 
batoid species. Our study revealed the occurrence of 17 
batoid and 5 shark species at similar depths. The domi- 
nant species observed by Campos (1986) in 1983-1984 
were rasptail skate, witch guitarfish, and giant electric 
ray, but only those first 2 species were abundant in 
our study. 
Contrary to our results, the brown smoothhound and 
Panamic stingray were absent or present in very low 
abundances during the study by Campos (1986). These 
results support reports based on the traditional eco- 
logical knowledge of fishermen that large aggregations 
of the Panamic stingray are part of recently observed 
shifts in the demersal assemblages off the Pacific coast 
of Costa Rica (senior author, personal observ. ). More- 
over, 11 species of batoids were found in our survey 
