Clarke et at: Elasmobranch bycatch from the shrimp trawl fishery along the Pacific coast of Costa Rica 
5 
Table 1 
Sampling effort for surveys of bycatch of elasmobranchs conducted along the Pacific coast of Costa Rica, Central America, in 
2008-2012 at 3 depth ranges: shallow ( <50 m), intermediate (50-100 m), and deep (>100 m). Number of trawling hours (h) 
and trawl hauls (Hauls) per geographic area and depth range. The highest sampling effort occurred in the central geographic 
region at depths <50 m with commercial surveys (underlined). 
2008 
2009 
2010 
2011 
2012 
Total 
Region Depth 
h 
Hauls 
h 
Hauls h 
Hauls 
h 
Hauls 
h 
Hauls 
h 
Hauls 
Commercial sampling 
Northern <50 m 
- 
- 
- 
- 
- 
- 
3.7 
2 
5.9 
1 
9.6 
3 
50-100 m 
- 
- 
- 
- 
10.3 
2 
9.3 
3 
- 
- 
24.1 
5 
Central <50 m 
- 
- 
- 
- 
24.6 
5 
61.8 
14 
28.6 
6 
115.0 
25 
50-100 m 
- 
- 
- 
- 
115.2 
20 
45.1 
10 
62.9 
14 
223.1 
44 
>100 m 
- 
- 
- 
- 
29.6 
14 
18.9 
9 
6.2 
4 
54.7 
27 
Southern 50-100 m 
- 
- 
- 
- 
- 
- 
6.1 
1 
- 
- 
6.1 
1 
>100 m 
- 
- 
- 
- 
12.5 
6 
- 
- 
53.2 
16 
65.7 
22 
Monitoring sampling 
Northern 50-100 m 
- 
- 
- 
- 
6.0 
1 
- 
- 
- 
- 
6.0 
1 
> 100 m 
- 
- 
- 
- 
1.4 
4 
- 
- 
- 
- 
1.4 
4 
Central <50 m 
- 
- 
- 
- 
0.7 
2 
- 
- 
- 
- 
0.7 
2 
50-100 m 
- 
- 
- 
- 
2.7 
8 
4.0 
12 
2.2 
6 
8.9 
26 
>100 m 
- 
- 
- 
- 
6.5 
19 
11.6 
35 
6.6 
19 
24.7 
73 
Southern 50-100 m 
- 
- 
- 
- 
0.3 
1 
- 
- 
- 
- 
0.3 
1 
>100 m 
- 
- 
- 
- 
1.5 
4 
- 
- 
- 
- 
1.5 
4 
Deepwater sampling 
Northern >100 m 
2.1 
8 
2.1 
8 
2.1 
8 
2.6 
10 
- 
- 
8.9 
34 
Central >100 m 
3.2 
12 
3.1 
12 
3.0 
12 
2.7 
10 
- 
- 
12.0 
46 
Southern >100 m 
2.3 
8 
2.0 
8 
1.7 
7 
1.3 
5 
- 
- 
7.0 
27 
Total 
12.1 
27 
7.3 
28 
218.0 
113 
167.3 
111 
165.6 
66 
570.0 
345 
common (1-5% of total abundance) and 11 were rare 
(<1% of total abundance). 
Species richness and distribution patterns of elas- 
mobranchs were examined across depths. Overall, 
2279 individuals of 24 species were recorded at shal- 
low depths (<50 m), 1642 individuals from 14 species 
were found at depths between 50 and 100 m, and only 
643 individuals from 7 species were observed at depths 
>100 m (Table 2). The number of species caught per 
trawl haul varied from 0 through 9. A significant, neg- 
ative relationship was detected between the average 
number of species per haul and depth (Spearman’s = 
-0.831, P<0.001; Fig. 2). 
Body size ranged from 21.8 to 138.0 cm TL for 
sharks and from 2.6 to 107.7 cm DW for rays (Fig. 3). 
The large number of small species (<50 cm TL or DW) 
were mainly from the families of Narcinidae, Urotry- 
gonidae, and Rajidae. The sicklefin smoothhound ( Mus - 
telus lunulatus), prickly shark ( Echinorhinus cookei), 
Pacific angel shark ( Squatina californica), and long- 
tail stingray (Dasyatis longa) were the largest species 
recorded; and these species collectively represented 
nearly 5% of the total elasmobranch abundance. The 
percentage of species that were small (<50 cm TL) 
was larger in shallow waters (depths <50 m. Fig. 3A) 
than at other depths (Fig. 3, B and C). Although most 
species presented narrow depth ranges, trends in size 
were apparent for some species with wide depth distri- 
butions (Fig. 3). Large, adult-size brown smoothhound 
dominated all depth categories. Smaller individuals of 
the rasptail skate were found in the shallower limit of 
the depth range for this species: 50-100 m. Likewise, 
average sizes of the sicklefin smoothhound, Peruvian 
torpedo (Torpedo peruana ), and witch guitarfish in- 
creased across depth ranges (Fig. 3). 
Elasmobranch presence in deepwater surveys was 
low, given that elasmobranchs were absent from 63% of 
the trawl hauls. Of the surveys in which elasmobranchs 
were present, 16.6% had a CPUE of 1-10 individuals/ 
hour and 20.4% had CPUE of 10-152 individuals/hour. 
The delta-GLM applied to the deepwater survey data 
revealed that depth had a significant effect on the den- 
sity of elasmobranch CPUE, and depth and latitude 
had a significant effect on the proportion of positive 
trawl hauls (Table 3). In monitoring surveys, we found 
that elasmobranchs were absent from 65.8% of all 
trawl hauls. The lognormal submodel of the delta-GLM 
applied to monitoring data did not detect significant 
effects. In contrast, the binomial submodel revealed 
that depth, latitude, and year had significant effects 
on elasmobranch presence (Table 3). In commercial 
surveys, 17.8% of trawl hauls did not result in elas- 
mobranch catch. The delta-GLM for commercial data 
indicated that depth was the only significant factor 
