Estimating Reef Fish Discard Mortality Using Surface and Bottom Tagging: Effects of Hook Injury, Barotrauma, and Multiple Captures

We estimated survival rates of discarded black sea bass in various release conditions using tag-recapture data.  Fish were captured with traps and hook and line from waters 29–34 m deep off coastal North Carolina, USA, marked with internal anchor tags, and observed for release condition.  Fish tagged on the bottom using SCUBA served as a control group.  Relative return rates for trap-caught fish released at the surface versus bottom provided an estimated survival rate of 0.87 (95% credible interval 0.67–1.18) for surface-released fish. Adjusted for results from the underwater tagging experiment, fish with external barotrauma had a median survival rate of 0.91 (0.69–1.26) compared with 0.36 (0.17–0.67) for fish with hook trauma and 0.16 (0.08–0.30) for floating or presumably dead fish.  Survival of black sea bass caught multiple times was not different than survival after a single capture.  Applying these condition-specific estimates of survival to non-tagging fishery data, we estimated a discard survival rate of 0.81 (0.62–1.11) for hook and line and 0.87 (0.67–1.17) for trap data.  The tag-return approach using a control group with no fishery-associated trauma represents a method to accurately estimate absolute discard survival of physoclistous reef species.