Brown et al.: Simple gear modifications for bycatch reduction in a shrimp trawl fishery 
381 
Table 5 
Results of the paired t-tests and randomization tests used to compare catch per unit of effort (CPUE), weight divided by tow time, 
between the control gear and 5 experimental (Exp.) gears tested in 2017 in Pamlico Sound and nearshore waters off North Caro¬ 
lina. Each of the 5 gears had a trawl efficiency device (TED) with reduced bar spacing, and bycatch reduction devices included state 
and federal fisheyes. Mean values of CPUE are reported in kilograms. An asterisk (*) indicates that data for a taxonomic group 
were not analyzed with a t-test because of low sample size. Values for invertebrates are for all non-commercial shrimp inverte¬ 
brates. n=number of tows. 
Gear 
Taxonomic 
group 
n 
Control 
Exp. 
t-test 
n 
Control 
Exp. 
Randomization 
Mean 
Mean 
Change 
(%) 
P-value 
Mean 
Mean 
Change 
(%) 
P-value 
Reduced-bar TED 
Finfish 
* 
* 
* 
* 
* 
5 
12.3 
12.9 
5.06 
0.732 
Shrimp 
* 
* 
* 
* 
* 
5 
18.7 
17.3 
-7.79 
0.827 
Invertebrates 
* 
* 
* 
* 
* 
5 
4.9 
6.8 
38.78 
0.281 
Elasmobranchs 
* 
* 
* 
* 
* 
4 
0.2 
0.4 
75.00 
0.487 
Reduced-bar TED + 4.13-cm codend 
Finfish 
20 
34.6 
26.7 
-22.80 
0.019 
22 
34.9 
27.8 
-20.42 
0.341 
Shrimp 
20 
12.1 
11.2 
-7.82 
0.294 
22 
11.6 
10.6 
-9.04 
0.556 
Invertebrates 
18 
2.3 
2.1 
-6.06 
0.692 
22 
2.07 
2.06 
-0.444 
0.993 
Elasmobranchs 
* 
* 
* 
* 
* 
3 
0.3 
0.1 
-80.00 
0.397 
Reduced-bar TED + double state 
Finfish 
30 
146.0 
98.5 
-32.60 
<0.001 
30 
146.0 
98.5 
-32.61 
0.002 
fisheyes + 4.13-cm codend 
Shrimp 
30 
2.9 
2.7 
-6.80 
0.039 
30 
2.9 
2.7 
-6.64 
0.598 
(summer) 
Invertebrates 
30 
17.2 
15.9 
-7.58 
0.086 
30 
17.2 
15.9 
-7.59 
0.505 
Elasmobranchs 
29 
3.0 
2.5 
-16.3 
0.184 
30 
2.87 
2.4 
-16.70 
0.425 
Reduced-bar TED + double state 
Finfish 
30 
57.5 
54.9 
-4.57 
0.670 
30 
57.5 
54.9 
-4.58 
0.890 
fisheyes + 4.13-cm codend 
Shrimp 
30 
9.8 
8.3 
-14.90 
<0.001 
30 
9.75 
8.3 
-14.83 
0.365 
(autumn) 
Invertebrates 
30 
8.2 
2.9 
-65.10 
0.001 
30 
8.20 
2.9 
-65.07 
<0.001 
Elasmobranchs 
28 
4.4 
1.9 
-57.10 
0.009 
29 
4.26 
1.8 
-57.29 
0.014 
Reduced-bar TED + double federal 
Finfish 
30 
75.6 
97.7 
29.30 
0.204 
30 
75.6 
97.7 
29.30 
0.250 
fisheyes + 4.13-cm codend 
Shrimp 
30 
17.3 
15.7 
-9.04 
0.002 
30 
17.3 
15.1 
-12.48 
0.234 
Invertebrates 
25 
2.2 
2.7 
21.90 
0.276 
30 
2.29 
2.9 
25.15 
0.455 
Elasmobranchs 
15 
1.3 
1.0 
-24.30 
0.271 
28 
0.904 
0.7 
-24.50 
0.360 
was found when this gear was used (Table 4). The paired 
t-test results indicate a significant decrease in shrimp 
catch for the gear with a reduced-bar TED, double state 
fisheyes, and a 4.13-cm codend that was tested in summer, 
the gear with a reduced-bar TED, double state fisheyes, 
and a 4.13-cm codend that was tested in autumn, and the 
gear with a reduced-bar TED, double federal fisheyes, and 
a 4.13-cm codend (all tested in 2017), whereas results of 
the randomization tests indicate no significant difference 
in shrimp CPUE for these gears (Table 5). 
The results of both tests indicate that the double fed¬ 
eral fisheye with a 4.76-cm codend (tested in 2015), the 
double federal fisheye with a 4.45-cm codend (tested in 
2016), the gear with a reduced-bar TED, double federal 
fisheye, and a 4.45-cm codend (tested in 2016), and the 
Virgil Potter BRD with a 4.45-cm codend (tested in 2016) 
exceeded the target of 40% reduction in finfish bycatch 
(Tables 3-5). None of those gears had a significant 
decrease in shrimp catches in either the paired t-tests or 
randomization tests. 
Gear costs 
Relative to the material and labor costs associated with 
constructing a single control trawl ($3000), additional 
costs associated with modifying the control gear to that 
of each experimental gear ranged from $110 to $1250 
(Table 1). An additional $600 per trawl above the cost 
of a typical control net was the minimum investment 
required to achieve reduction >40% in finfish bycatch in 
this study. 
Discussion 
Gear performance 
The goal to achieve a reduction of 40% in finfish bycatch 
did not allow this study to evaluate the effects of single 
gear modifications, as is typically conducted in BRD test¬ 
ing (Brewer et al., 1998). However, the bycatch reduction 
goal was achieved by using BRD combinations chosen 
through a collaborative process that relied on expert opin¬ 
ions and past research. Four of the 14 gear combinations 
that were tested met the immediate project goal, and the 
results of this study provide direction for future testing 
and for making interim management recommendations 
(Tables 3 and 4). In fact, the NCMFC voted in May 2018 
to implement these gear combinations as a requirement, 
beginning in 2019 on larger vessels (> 12 m) fishing in 
