Campbell et al.: Release mortality in the fishery targeting Lutjcinus campechanus 
289 
14 
Depth (m) 
Figure 2 
Depth-frequency distribution associated with estimates (n= 75) of release 
mortality for red snapper (Lutjanus campechanus) in the Gulf of Mexico. 
Values were compiled from 11 studies and were included in the meta- 
analytical model developed in this study. 
coefficients indicated that the commercial fishing sector 
was the most influential factor that increased mortal- 
ity and that the interaction and winter terms were the 
most influential factors that reduced mortality. That 
the term for the timing :i: venting interaction was sta- 
tistically significant indicates that the effect of vent- 
ing was dependent on the timing of the estimate and, 
therefore, indicates that immediate measurements of 
mortality (e.g., surface-release methods) were affected 
significantly decreased by venting. The venting coeffi- 
cient was positive, indicating that, for delayed esti- 
mates, venting would increase mortality. 
Removal of estimates of release mortality in the 
commercial sector had little effect on model outcomes 
(i.e., significant coefficients) compared with model runs 
that included that data. The amount of heterogene- 
ity in effect size from the mixed-effects model without 
commercial-sector data was estimated to be 0.29. Co- 
chran’s Q-test for the mixed-effects model also showed 
significant residual heterogeneity ($£=440. 81, df=56, 
P<0.0001), indicating that the model did not fully ex- 
plain the observed variation in release mortality es- 
timates. Model coefficients indicated that depth was 
the most influential factor that increased mortality 
and that the winter and spring seasonal conditions 
were important in reduction of mortality. Significant 
effects in this second model included the following co- 
efficients: intercept, depth, timing*venting interaction, 
winter, and spring (Table 3). Timing, 
venting, fall, annual, and hook-type 
effects were nonsignificant. Conserva- 
tion of the results despite removal of 
the commercial data indicated that 
the model was largely driven by rec- 
reational data. 
Predicted rates of discard mortality 
by depth, mode, and season were de- 
rived by weighting model coefficients 
generated through the use of the full 
complement of data (i.e., commercial 
data were included). Average predic- 
tions and treatment-specific predic- 
tions were generated by weighting 
the coefficients accordingly. Over a 
depth range of 10-100 m, average 
model predictions (equal weighting 
of coefficients) of release mortalities 
ranged between 19% and 67% (Fig. 3; 
Table 4). As indicated by the statisti- 
cal significance of the timing*venting 
interaction, the predicted rates of re- 
lease mortality by venting treatments 
were dependent on whether a study 
relied on the surface-release method; 
this method produces immediate es- 
timates, and other methods result in 
delayed estimates (Fig. 4). Immediate 
estimates indicated that venting de- 
creased mortality rates, but delayed estimates indicat- 
ed that venting increased mortality rates. Regardless 
of the model run, the winter and spring terms were sig- 
nificant and the predicted release mortality rates were 
Table 2 
Model coefficients, standard errors of the mean (SE), 
and P-values estimated in a meta-analysis of release 
mortality of red snapper ( Lutjanus campechanus) in the 
Gulf of Mexico. This meta-analysis included both recre- 
ational and commercial data. Significant coefficients are 
highlighted with asterisks (*** P<0.0001, ** PcO.001, * 
P<0.05), and “ns” indicates nonsignificant coefficients. 
Data type 
Coefficient 
SE 
P 
Significance 
Intercept 
-1.9136 
0.7085 
0.0069 
** 
Depth 
0.0209 
0.0046 
<.0001 
*** 
Sector 
2.2769 
0.4228 
<.0001 
*** 
Timing 
0.5304 
0.7009 
0.4492 
ns 
Venting 
0.6955 
0.6732 
0.3016 
ns 
Timing*Venting 
-1.4858 
0.7419 
0.0452 
* 
Winter 
-0.9905 
0.2789 
0.0004 
*** 
Spring 
-0.7701 
0.2872 
0.0073 
** 
Fall 
-0.3364 
0.235 
0.1524 
ns 
Annual 
-0.3668 
0.3522 
0.2977 
ns 
Hook type 
0.0139 
0.2107 
0.9472 
ns 
