Rogers et a\. : Effectiveness of bycatch reduction devices in Louisiana inshore waters 
563 
Table 4 
Comparisons of numbers and biomass of fish and shrimp collected by the four bycatch reduction device (BRD) nets and corre- 
sponding control nets in the three areas. SD is the standard deviation of the difference. Significance levels are 0.01 (**) and 0.05 
(*). n= 24. Superscripted letters denote significance levels of paired t-tests on log-transformed data: 0.01 (“), 0.05 t b ). 
Numbers Biomass (g) 
BRD and 
type of 
catch 
Mean catch/tow 
Percent 
catch 
difference 
Mean catch/tow 
Percent 
catch 
difference 
Area 
Control 
Device 
SD 
P>t-value 
Control 
Device 
SD 
P>t-value 
Authement-Ledet 
Fish L. Borgne 
64.6 
38.4 
-41 
45.7 
0 Ql **“ 
1,119.9 
732.7 
-35 
588.1 
0 . 01 **“ 
L. Barre 
202.7 
134.8 
-34 
122.6 
0 . 01 **“ 
2,425.2 
1,458.9 
-40 
1,302.6 
0 . 01 **“ 
Calcasieu L. 
244.0 
153.8 
-37 
114.7 
0 . 01 **“ 
4,080.2 
2 , 200.8 
-46 
1,584.7 
0 . 01 **“ 
Shrimp 
L. Borgne 
49.0 
35.8 
-27 
21.3 
0 . 01 ** 
381.7 
285.4 
-25 
178.1 
0 . 01 ** 
L. Barre 
90.5 
86.7 
-4 
40.1 
0.64 
613.6 
579.7 
-6 
233.9 
0.49 
Calcasieu L. 
115.1 
85.5 
-26 
89.4 
0 . 12 6 
454.1 
387.5 
-15 
300.6 
0.29 
Lake Arthur 
Fish L. Borgne 
65.4 
47.0 
-28 
36.4 
0 . 02 * ft 
1,365.2 
1,072.9 
-21 
638.6 
0.03* 
L. Barre 
215.3 
151.3 
-30 
149.3 
0.05* 
3,046.8 
2,263.0 
-26 
2,441.9 
0.13 
Calcasieu L. 
233.4 
205.6 
-12 
152.9 
0.38 
4,301.0 
3,511.9 
-18 
1,235.3 
0 . 01 **“ 
Shrimp 
L. Borgne 
57.0 
47.0 
-18 
20.1 
0 . 02 *“ 
389.1 
350.6 
-10 
142.5 
0 . 20 “ 
L. Barre 
95.3 
70.3 
-26 
39.5 
0 oi **“ 
649.4 
509.4 
-22 
239.9 
0 . 01 **“ 
Calcasieu L. 
127.4 
95.4 
-25 
89.4 
0.09 
503.5 
415.1 
-18 
252.1 
0.10 
Cameron 
Fish L. Borgne 
89.8 
32.5 
-64 
113.0 
0 . 02 *“ 
1,987.7 
1,170.2 
-41 
1,361.9 
0 . 01 **“ 
L. Barre 
188.9 
98.6 
-48 
75.1 
0 oi **“ 
2,693.3 
1,776.4 
-34 
869.6 
0 . 01 **“ 
Calcasieu L. 
266.5 
133.9 
-50 
125.9 
0 . 01 **“ 
4,524.6 
3,257.7 
-28 
1,402.8 
0 . 01 **“ 
Shrimp 
L. Borgne 
59.8 
45.0 
-25 
23.6 
0 oi **“ 
419.8 
338.2 
-19 
145.7 
0 oi *** 
L. Barre 
108.2 
97.5 
-10 
42.8 
0.23 
719.6 
655.1 
-9 
225.8 
0.18 
Calcasieu L. 
164.8 
136.6 
-17 
126.7 
0.29 6 
598.4 
507.7 
-15 
278.4 
0.12 
Eymard 
Fish 
L. Borgne 
81.6 
114.4 
40 
83.9 
0.07“ 
1,970.0 
1,288.0 
-35 
1,394.5 
0.03* 
L. Barre 
201.8 
301.0 
49 
193.1 
0 . 02 *“ 
2,724.3 
2,554.9 
-6 
2,158.8 
0.70 
Calcasieu L. 
287.8 
303.7 
6 
195.7 
0.69 
4,246.5 
3,376.1 
-20 
2,493.5 
0 . 10 6 
Shrimp 
L. Borgne 
52.7 
84.1 
60 
79.2 
0.06“ 
365.2 
510.4 
40 
343.3 
0.05* 
L. Barre 
97.5 
120.6 
24 
34.1 
0 oi **“ 
672.8 
730.8 
9 
166.2 
0 . 10 6 
Calcasieu L. 
146.5 
204.5 
40 
145.4 
0.06“ 
513.5 
694.8 
35 
450.7 
0.06“ 
trips or evaluating fewer BRD’s. Increasing the trawl- 
tow duration decreases the ability of a fish to main- 
tain swimming speed (Bainbridge, 1960). Reductions 
over longer tow periods may differ; if most reduction 
occurs during haulback, fish may be too exhausted 
to escape. Longer tows also increase the chances of 
catching large quantities of fish and shrimp that may 
clog the net and cause organisms to be released from 
the BRD. 
In terms of abundances and size distributions, 
bycatch varied between the areas and seasons; some 
species were very abundant in one or two areas. The 
capability of a BRD to reduce fish or shrimp depends 
on the species assemblage present in an area. A BRD 
may work well in one area under certain conditions 
but perform poorly in another area owing to assem- 
blage differences. Species-specific size selectivity has 
been reported in other studies (e.g. Rulifson et al., 
1992). Of the four BRD’s, the Cameron had the best 
overall fish reduction. However, if spot and gulf men- 
haden were the most abundant species in an area, 
the Authement-Ledet may be a better choice. By catch 
reduction devices may have to be selected for par- 
ticular areas or seasons, depending on the type and 
size distributions of predominant bycatch species, 
because a particular device may not be as effective 
in all areas or at all times of the year. 
The high shrimp losses from the BRD’s evaluated 
in this study would most likely be unacceptable for 
commercial operations. However, further modifica- 
tions to these devices, such as altering the size or 
location of escape openings, could reduce these losses. 
