216 
Fishery Bulletin 95(2), 1997 
1 1 
CO CM C 
F 
ii ii l. 
6 1 
4- 
2- 
i 
** ■ 1 
il 
<D 
-Q 
E 
I e. 
** 
1 
ii ii n H 
3 1 
i 
» ii ii H 
c 
Standard Ng 
Blubber-chute 
S emf 
C Blubber-chute 
U1 
"o' 
O Fisheye 
Blubber-chute 
5' 
c 
0) 
Q. 
Standard Ng 
Fisheye 
Standard Ng 
EMF 
Discussion 
This study has confirmed the effectiveness of the 
Mordmore grid in reducing bycatch while maximiz- 
ing catches of prawns in NSW estuarine prawn-trawl 
fisheries (see also Broadhurst and Kennelly, 1996; 
Broadhurst et al., 1996). By comparing several sec- 
ondary BRD’s attached to a Nordmpre grid, we have 
also provided information on the relative effective- 
ness of these designs and their suitability in the HR 
prawn-trawl fishery. 
The results from experiment 1 showed that apart 
from a significant reduction in the number of non- 
commercial species with the Allerio Brothers grid, 
compared with the square-mesh panel, there were 
no detectable differences in the relative performance 
of any of the secondary BRB’s tested (Table 1). 
Compared with the commercially used blubber 
chute, all three designs incorporating Nordmpre grids 
in experiment 2 (the standard Nordmpre grid and 
the Nordmpre grid incorporating the EMF and 
fisheye) significantly increased the catches of prawns 
(by 24%, 41%, and 23%, respectively) while signifi- 
cantly reducing the total bycatch (by 58%, 45%, and 
55%, respectively) (Fig. 5; Table 2). In earlier papers 
(Broadhurst and Kennelly, 1996; Broadhurst et al., 
1996), we concluded that the prawn-retention char- 
acteristics of the Nordmpre grid were attributed to 
its ability to remove seaweed and debris more effec- 
tively. In the present study we observed that, at the 
end of each tow, those designs incorporating the 
Nordmpre grid were observed to be relatively free of 
seaweed and debris, whereas the blubber chute of- 
ten had large quantities entangled between the 
meshes, which may have decreased the lateral open- 
ings between the meshes in the blubber chute and 
contributed towards the escape of prawns with this 
design. Further, because Kolmogorov-Smirnov tests 
