292 
Fishery Bulletin 107(3) 
unadjusted mean ±SE of up to 53.4 ±6.5%; Tables 2 
and 3, Fig. 2A, P<0.05). This clear trend in deaths 
precluded any interaction between sorting method and 
delay, although these means are presented in Fig. 2A 
for ease of interpretation (Table 3, P>0.1). The first 
model also detected a significant negative relationship 
between mortality and salinity at the bottom of the 
Table 2 
Percentage of total mortalities of trawled-and-discarded 
school prawns (Metapenaeus macleayi) adjusted for deaths 
to the controls for the sorting treatments of interest (2- 
min and 15-min delays in the conventional and water 
trays) at the four sampling times (immediately [T 0 ], and 
after 24 hr [T 24 ], 72 hr [T 72 ], and 120 hr [T 120 ]) in the 
Clarence and Hunter rivers during 2007 and 2008. 
Conventional tray Water tray 
2-min 
15-min 
2-min 
15-min 
delay 
delay 
delay 
delay 
Clarence River 
T 0 
3.8 
20.7 
0.0 
5.2 
t 24 
21.4 
37.0 
15.7 
16.6 
T 72 
25.8 
40.0 
15.5 
18.2 
T 120 
22.8 
41.4 
6.3 
17.8 
Hunter River 
T 0 
5.7 
15.7 
0.0 
3.0 
T'24 
29.8 
29.0 
13.6 
18.1 
T72 
26.4 
35.7 
20.2 
21.5 
Tl20 
20.6 
34.8 
18.6 
8.9 
river (Table 3, P<0.01). The same significant negative 
relationship with mortality was observed for salinity in 
the water tray in the second model (Table 3, P<0.01). 
The third model identified total catch weight as having 
a significant positive relationship with the mortality of 
conventionally handled school prawns, whereas cloud 
cover had a negative relationship (Table 3, P<0.05). 
ANOVA returned significant P-ratios for the treat- 
ment of prawns and sampling times for the levels of 
L-lactate in surviving school prawns from one randomly 
selected fishing day (Table 4 , PcO.Ol). There was no 
interaction between these factors (P>0.05), but the cor- 
responding means are presented for clarity (Table 4, 
Fig. 2B). Student-Newman-Keuls tests revealed that the 
overall mean ±SE concentration of L-lactate in control 
school prawns (4.63 ±0.76 pmol/g) was significantly low- 
er than all other treatments; which remained similar at 
between 6.77 ±1.28 and 8.40 ±1.21 pmol/g (P<0.05). Ir- 
respective of the treatment of school prawns, all prawns 
had significantly greater concentrations of L-lactate at 
T 0 (13.49 ±0.81 pmol/g) than at T 72 ( 3.48 ±0.28 pmol/g) 
and T 120 ( 3.78 ±0.27 pmol/g) (Fig. 2B, P<0.05). 
Hunter River experiment 
A total of 2400 school prawns were caged across the con- 
trol and four treatment groups; of which 10 (in one cage 
from the 15-min conventional-tray treatment) escaped 
prior to their designated sampling time (T 120 ). Similar 
to the Clarence River experiment, control deaths ranged 
between predicted means of 0.0% and 11.7%, providing 
adjusted total mortalities of up to 35.7% and 21.5% for 
the 15-min conventional- and water-tray treatments, 
respectively (Table 2, Fig. 3). 
Table 3 
Summary of variables tested in mixed-effects logistic models for their independence of the mortality of trawled-and-discarded 
school prawns ( Metapenaeus macleayi) in the Clarence and Hunter rivers during 2007 and 2008. Four separate models were 
applied: the first to all of the available data for trawled-and-discarded individuals (All); the second and third to only those dis- 
carded from the water tray (WT) and conventional tray (CT) treatments, respectively; and the fourth to the data for the controls 
(C). O P>0.1; • P<0.1; *P<0.05; **P<0.01; — , term not considered in the model. 
Clarence River 
Hunter River 
Variable 
All 
WT 
CT 
C 
All 
WT 
CT 
C 
Sampling time 
** 
** 
** 
** 
** 
** 
** 
** 
Sorting method (M) 
** 
- 
- 
- 
** 
- 
- 
- 
Sorting delay (S) 
** 
* 
** 
- 
O 
O 
** 
- 
MxS 
O 
- 
- 
- 
O 
- 
- 
- 
Total weight of catch 
« 
O 
** 
- 
** 
** 
0 
- 
Salinity 
bottom 
** 
O 
O 
O 
O 
surface (water tray) 
- 
** 
- 
- 
- 
O 
- 
- 
Dissolved oxygen (water tray) 
- 
O 
- 
- 
- 
O 
- 
- 
Air temperature 
- 
- 
O 
- 
- 
- 
O 
- 
Cloud cover 
- 
- 
* 
- 
— 
" 
O 
— 
