10 
) 
Fishery Bulletin 1 14(1) 
Table 4 
Spatial distribution for sex and maturity ratios of the elasmobranch assemblage, by depth range (<50 m, 50-100 m, 
or >100 m) and diel period (day or night), along the Pacific coast of Costa Rica, Central America, in 2010-2012. The 
degrees of freedom (df), deviance, residual deviance (Res. dev), and probability ( P ) of the binomial generalized linear 
models (GLMs) applied to both maturity and sex ratios of the most abundant elasmobranch species. Significant P- 
values are in bold (a=0.05). The following species abbreviations are used: MHE (brown smoothhound [Mustelus henlei]), 
MLU (sicklefin smoothhound [Mustelus lunulatus]), UAS (Panamic stingray [ Urotrygon aspidura}), UCH (blotched 
stingray [Urotrygon 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 [Narcine 
entemedor ]), NYE (vermiculate electric ray [Narcine vermiculatus]), and TPE (Peruvian torpedo [Torpedo peruviana ]). 
Sex ratios Maturity ratios 
Species 
Factors 
df 
Deviance 
Res. dev. 
P 
df 
Deviance 
Res. dev. 
P 
MHE 
Intercept 
1 
358.0 
1 
612.1 
Depth 
2 
7.7 
350.4 
0.43 
2 
50.0 
562.1 
0.04 
Diel period 
1 
9.7 
340.7 
0.15 
1 
16.5 
545.6 
0.14 
MLU 
Intercept 
1 
24.2 
1 
53.5 
Depth 
2 
2.0 
22.3 
0.41 
2 
6.1 
47.5 
0.56 
Diel period 
1 
0.0 
22.3 
0.95 
1 
0.0 
47.5 
0.98 
UAS 
Intercept 
1 
25.4 
1 
74.9 
Depth 
1 
5.4 
20.0 
0.04 
1 
0.1 
74.8 
0.83 
Diel period 
1 
1.5 
18.6 
0.27 
1 
29.0 
45.8 
0.00 
UCH 
Intercept 
1 
35.0 
1 
43.4 
Depth 
1 
3.3 
31.7 
0.47 
1 
12.3 
31.1 
0.20 
Diel period 
1 
3.2 
28.4 
0.47 
1 
1.8 
29.3 
0.59 
URO 
Intercept 
1 
8.7 
1 
21.3 
Diel period 
2 
0.0 
8.6 
0.99 
1 
18.3 
3.0 
0.01 
RVE 
Intercept 
1 
196.1 
1 
538.0 
Depth 
2 
10.4 
185.7 
0.16 
2 
70.3 
467.7 
0.01 
Diel period 
1 
0.2 
185.6 
0.80 
1 
2.1 
465.5 
0.58 
ZXY 
Intercept 
1 
118.8 
1 
222.6 
Depth 
2 
1.8 
117.1 
0.69 
2 
19.3 
203.2 
0.09 
Diel period 
1 
0.3 
116.8 
0.74 
1 
6.9 
196.3 
0.19 
DOM 
Intercept 
1 
23.5 
1 
12.5 
Depth 
1 
1.9 
21.6 
0.47 
1 
2.8 
9.8 
0.20 
Diel period 
1 
1.6 
19.9 
0.51 
1 
1.8 
8.0 
0.29 
NEN 
Intercept 
1 
31 
1 
34.2 
Depth 
1 
0.0 
31.0 
0.92 
1 
7.0 
27.2 
0.02 
Diel period 
1 
1.2 
29.8 
0.34 
1 
2.1 
1.8 
0.19 
NVE 
Intercept 
1 
40.9 
1 
40.9 
Diel period 
1 
19.4 
21.5 
0.10 
1 
1.2 
21.5 
0.10 
TPE 
Intercept 
1 
105.5 
1 
77.3 
Depth 
Z 
1.4 
104.0 
0.54 
2 
1.8 
75.5 
0.51 
Diel period 
1 
7.0 
97.1 
0.02 
1 
0.4 
75.2 
0.60 
The elasmobranch assemblages caught by the shrimp 
trawl fishery were slightly influenced by diel period. 
Most elasmobranch species display higher activity lev- 
els during the night — a characteristic mainly related to 
foraging or social refuging behaviors (Wearmouth and 
Sims, 2008; Jacoby et al., 2012; Espinoza et al., 2011). 
Catch of elasmobranchs in trawl hauls, therefore, is ex- 
pected to be higher during the day than at night; how- 
ever, very few studies have addressed diel periodicity 
of bycatch (Molina and Cooke, 2012). The results of this 
study support the assumption that elasmobranch catch 
is higher during the day than at night. 
Although the small sample size prevented us from 
detecting clear patterns for most species, a higher 
proportion of female Peruvian torpedo and immature 
round stingrays were found during the day than at 
night. The higher abundance of Peruvian torpedo dur- 
ing the day may be a result of its feeding behavior. 
The Pacific electric ray ( Torpedo californica ) is a bot- 
tom ambush predator during the day and actively for- 
