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Fishery Bulletin 1 12(4) 
Figure 5 
Predicted relationship between depth and release mortality (propor- 
tion) of red snapper (Lutjanus campechanus ) in the Gulf of Mexico 
derived from the meta-analytical model for the winter, spring, sum- 
mer, and fall seasons and annual classification. Results indicate that 
cooler seasons, and therefore water temperature, reduces release 
mortality. 
face-release studies also inject uncertainty 
into assessment models because of the un- 
known misclassification rates that result 
from the use of submergence as a proxy 
for mortality. Submergence data should be 
collected and used only as a last resort in 
the estimation of release mortality. 
Both model runs, with and without the 
data from the commercial fishing sector, in- 
dicated that venting was not significant — 
a finding that agrees with the conclusions 
in Wilde (2009) that there was no evidence 
for an effect of venting. Two of the studies 
that produced delayed estimates specifi- 
cally tested the effects of venting after fish 
were submerged in cages to at least 2 atm 
of pressure (Gitschlag and Renaud, 1994; 
Render and Wilson, 1994). Submergence to 
2 atm halves gas volume in the air bladder 
and effectively recompresses the fish. Both 
of these caging studies reported no differ- 
ence in survival by venting treatments, 
but neither study addressed the issue of 
recompression. Recompressing the gas 
bladder may have had the same effect as 
venting the fish and, perhaps, explains the 
lack of a difference in survival between 
venting treatments. Ultimately, these cag- 
ing studies lend insight in regard to vent- 
ing versus recompression, but they are not 
reflective of day-to-day fishery operations 
in which fish are released at the surface. 
Venting is best evaluated with tag- 
and-recapture studies in which fish are 
released as they would be in regular fish- 
ery operations. The only tag-and-recapture study that 
directly compared venting treatments, and that was 
available for inclusion in either meta-analysis, simply 
evaluated recapture rates and did not generate a mod- 
el for estimation of release mortality (Burns et al. 1 ). 
Furthermore, estimates from the Burns et al. 1 tag-and- 
recapture study did not account for spatial issues; nor 
did it incorporate fishing effort, making interpretation 
of the results problematic. Recently developed tag-and- 
recapture models from other fisheries that use fishery- 
dependent data and incorporate fishing effort, hook 
type, and venting procedures into the estimates should 
provide a more robust method to test venting (Hueter 
et al., 2006; Sauls and Ayala, 2012; Sauls, 2014). The 
interaction result indicates that recompression of fish 
may be a viable alternative to venting, but if a recom- 
pression device is not available, then venting at least 
improves the likelihood that a fish can submerge and 
return to protective habitat. 
Recent research in the red snapper fishery has been 
focused on bottom-release devices, 2 of which have been 
tested experimentally. The use of a bottom-release de- 
vice is similar to venting in that the goal is to reverse 
the effects of barotrauma, but instead of deflating the 
bladder by puncture it is deflated by recompression 
at depth. Diamond et al. 7 tested the Shelton Fish De- 
scender 9 (Shelton Products, Newark, CA) and showed 
that the use of that bottom-release device did not im- 
prove survival over the use of a treatment in which fish 
were vented and released at the surface. Another de- 
vice that releases fish at a preset depth through a pres- 
sure-sensitive clamp was tested in a different study 
that showed that fish released through the use of that 
device are more likely to survive than fish vented and 
released at the surface (Stunz and Curtis 10 ). At this 
time, it is difficult to discern if the differences between 
these 2 experiments were due to the gear used or some 
other effect, such as low sample sizes. The significant 
interaction term from the results of these studies in- 
dicates that release devices may be useful in reducing 
mortality in lieu of venting. More studies are needed 
9 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
10 Stunz G. W., and J. Curtis. 2012. Examining delayed mor- 
tality in barotrauma afflicted red snapper using acoustic te- 
lemetry and hyperbaric experimentation. SEDAR31-DW21, 
15 p. [Available from http://www.sefsc.noaa.gov/sedar/.] 
