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Fishery Bulletin 1 12(4) 
Results 
Estimates of release mortality ranged from 0% to 91% 
over the collection of studies evaluated (Table 1, Fig. 
1). The lowest estimate of 0% was associated with a 
hyperbaric-chamber study (Burns et al. 6 ), and the high- 
est value of 91% was associated with the only data 
available for the commercial fishing sector. The most 
common method used in these studies was surface re- 
lease, followed by passive tagging, caging, hyperbaric 
chamber, and acoustic tagging (Table 1, Fig. 1). Release 
estimates were calculated most frequently from sum- 
mer data, followed by winter, fall, spring, and annual 
(Table 1). Studies were conducted primarily at depths 
that ranged between 20 and 50 m; infrequent repre- 
sentation was found outside that range (Fig. 2). Esti- 
mates mainly were associated with the recreational 
fishing sector or with methods and gear commonly used 
in recreational fishing. Commercial fishing data were 
represented by a single study. Estimates of hook type 
were fairly balanced between the studies that used J- 
hooks and the ones that used circle hooks; fewer stud- 
ies used a mixture of hook types. Studies that used a 
mixture of hook types were associated most commonly 
with those studies that used direct observations in the 
fishery and for which gear choice was, therefore, reflec- 
tive of common fishing practices. Studies in which a 
venting treatment was used 100% of the time always 
were associated with controlled scientific experiments 
(i.e., they did not involve direct observations of the 
fishery). Regardless of the fishing sector, nonventing 
estimates were associated most frequently with stud- 
ies where fishing practices were observed from working 
vessels. 
Results of the meta-analysis of the full complement 
of data showed significant effects for the following coef- 
ficients: intercept, depth, sector, timing*venting inter- 
action, winter, and spring (Table 2). The timing, vent- 
ing, fall, annual, and hook-type effects were nonsignifi- 
cant. The amount of heterogeneity in effect size from 
the mixed-effects model was estimated to be 0.31. Co- 
chran’s Q-test for the mixed-effects model also showed 
significant residual heterogeneity (Qe=663.20, df-64, 
P<0.0001), indicating that the model did not fully ex- 
plain the observed variation in estimates of release 
mortality. Depth was the most important factor deter- 
mining release mortality and consistently showed a 
positive relationship with mortality (Figs. 3-6). Model 
40 50 60 
Depth (m) 
+ Acoustic tagging x Passive tagging o Surface release A Cage 
Figure 1 
Scatter plot of estimates (proportions) of release mortality by depth (0-100 m) for red 
snapper ( Lutjanus campechanus) in the Gulf of Mexico determined from 11 studies of 4 
types: acoustic tagging (+), passive tagging (*), surface release (o), and caging (A). The 
values represented in this plot were used in the meta-analytical model of this study and 
are also included in Table 1. 
