Effects of venting and recompression on post-release behavior of snapper-grouper species
Hager, Zaida Faye
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Many traditional fisheries management regulations result in regulatory discards, which may experience mortality due to factors such as barotrauma. This study investigated the effects of common catch-and-release procedures as well as immediate release condition on delayed post-release behavior and mortality of selected recreationally and commercially important snapper grouper species: Black Sea Bass, Red Porgy, Red Snapper, and Gray Triggerfish. Fish were examined for barotrauma and treated using one of two common methods: venting and recompression, then released into a vertical enclosure equipped with underwater video cameras. Videos were analyzed to determine post-release behavior for up to 2.5 hours. This study assumed post-release behavior can predict likelihood of mortality. Proportion of time spent in normal behavior and time to recover to normal behavior were used as indicators of mortality risk. They were compared to immediate release observations (<i>e.g.</i> fish swimming down fast or slow, or floating at the surface) in attempt to determine relationships between immediate and delayed mortality. Handling time and immediate release condition had significant effect on both the amount of time fish spent in normal swimming behavior and time it took fish to recover. Handling time and release condition may be good predictors of mortality. Treatment did not have a significant effect on post-release behavior, but did appear to decrease recovery time. Ultimately, handling time was the most important predictor of post-release behavior regardless of treatment. The faster a fish was able to return to depth, the higher the likelihood of survival, irrespective of the release method. However, as venting involves injuring a fish by puncturing the swim bladder, I recommend using descending devices to rapidly recompress fish. Though previous mortality estimates based on release condition may lack accuracy, release condition is a good predictor of post-release behavior, and could be a good predictor of delayed mortality with more research on the relationship of immediate release condition to delayed mortality.