Broadhurst et al.: Evaluations of Nordmore grid and secondary bycatch-reduction devices 
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Figure 4 
Diagrammatic representation of the Allerio Brothers grid, dia = diameter. 
replicates) in experiment 1 were analyzed by using 
two-tailed, paired f-tests. Because a previous experi- 
ment in the Clarence River prawn-trawl fishery 
showed that the Nordmpre grid caught more prawns 
than the blubber chute (Broadhurst and Kennelly, 
1996), in experiment 2 we tested the hypothesis that 
each of the three designs incorporating a Nordmpre 
grid caught more prawns but less bycatch than the 
commercially used blubber chute. These data were 
analyzed by using one-tailed paired Gtests. Size fre- 
quencies of prawns from experiment 2 were graphed 
and compared by using two-sample Kolmogorov- 
Smirnov tests (P=0.05). 
Results 
Experiment 1 (comparisons of secondary 
BRD's) 
Apart from a significant reduction in the number of 
noncommercial species caught as bycatch by the 
Allerio Brothers grid, compared with the number 
caught with the square-mesh panel, there were no 
other detectable differences between any of the sec- 
ondary BRD’s tested (Table 1). However, because 
previous studies in the Gulf of Mexico showed that 
the EMF and fisheye were most effective in exclud- 
ing small fish from the codend (Watson and Taylor 2 ; 
Watson 3 ), these two designs were tested further in 
experiment 2. 
Experiment 2 (comparison of two secondary 
BRD's, standard IMordmore grid and blubber 
chute| 
Compared with the commercially used blubber chute, 
the standard Nordmpre grid, EMF, and fisheye all 
significantly increased the weight of prawns caught 
(means increased by 24%, 41%, and 23%, respec- 
tively) and decreased the weight of total bycatch 
(means reduced by 58%, 45%, and 55%, respectively) 
and number of noncommercial species in bycatch 
(Fig. 5, A, B, and H; Table 2). The fisheye also sig- 
nificantly reduced the mean number of catfish caught 
by 79.5% (there were insufficient catfish from the 
