Abstract-The value of catch-and-release fishing as a conservation measure is highly dependent upon rates of discard frequency and release mortality. Therefore, it is important to understand how estimates of these variables are affected by factors such as capture depth and water temperature. The meta-analytical approach to modeling used here for red snapper (Lutjanus campechanus) in the Gulf of Mexico provides a robust method for dealing with studyspecific differences in experimental protocols and for estimating release (discard) mortality as a function of key factors. Results of this analysis showed significant increases in mortality by depth and for the commercial sector. The most consistent result was the positive correlation between depth and estimates of release mortality, a relationship that was present regardless of study method, fishing sector, hook type used, or season of study. The effect of venting (deflating the swim bladder by puncture) was dependent on whether the study produced estimates of immediate or delayed mortality. Immediate estimates indicated that mortality rates are lowered by venting whereas delayed estimates indicated that venting increased mortality rates. This result is largely reflective of the use of submergence ability, from surface-release studies, as a proxy for mortality. The model's interaction result indicates that recompression of fish may be a viable alternative to venting and that, if a recompression device is not available, venting at least improves the likelihood that a fish can submerge and return to protective habitat. The depth-based functional relationships developed in this model were used in the most recent red snapper stock assessment in 2012, and that use was a change from previous assessments where region-specific point estimates were used.
Fishery regulations mandate the release of many caught fish, elevating the importance of having accurate estimates of discard mortality. Red Snapper Lutjanus campechanus are overfished and undergoing overfishing in the southeast U.S. Atlantic, in part due to the high number of releases that die from discard mortality. We used acoustic telemetry to track the fine-scale movements of hook-and-line-caught Red Snapper released with descender devices at a hardbottom site off North Carolina, USA. Movement characteristics of known-fate (live and dead) Red Snapper were used to infer fates of other individuals, from which we generated a proportional mortality estimate of 0.08 (95% CI = 0.00-0.17) for successfully descended Red Snapper with no hook trauma. This best-case mortality estimate was then used in a simulation to estimate overall Red Snapper discard mortality for the recreational fishery in the southeast U.S. Atlantic based on hooking location and a depth of approximately 37 m. For this fishery, we estimated the median proportional rate of discard mortality to be 0.13 (2.5% and 97.5% percentiles = 0.10, 0.17) if all released individuals were descended. This estimate is lower than the discard mortality values (~0.2-0.3 for the recreational fishery) used in the current Red Snapper stock assessment, but it is likely not reflective of the current reality given that descender use is not 100% in this region; this estimate is also depth specific. Increased use of descender devices will reduce discard mortality for Red Snapper, enhancing efforts to rebuild this stock.
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