Rudershausen, P. J., J. A. Buckel, and J. E. Hightower. 2014. Discard mortality of a U.S. South Atlantic reef fish estimated from surface and bottom tagging. Canadian Journal of Fisheries and Aquatic Sciences 71:514-520.
Abstract
Discard mortality may contribute to the overall rate of fishing mortality for reef fishes with physoclistous bladders due to barotrauma. 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 a narrow depth range (29 - 34 m) off the coast of North Carolina, USA, marked with internal anchor tags, and observed for release condition. We also tagged fish on the bottom using SCUBA; these fish served as a control group for which we assumed survival was similar to fish that were never captured. Survival by release condition was estimated as the ratio of return rate of fish in each compromised condition relative to return rate of the control group. Discard survival for the hook and line and trap fisheries in this region was estimated by applying condition-specific survival rates to fish released in each condition during independent (non-tagging) recreational and commercial fishing operations. Relative to fish tagged on the bottom, the survival rate of surface-released fish in the best condition was 0.94 (95% credible interval 0.72 – 1.32). Adjusted for results from the underwater tagging experiment, fish with evidence of external barotrauma had a median survival rate of 0.98 (0.73 – 1.41); fish with hook trauma had a median survival rate of 0.39 (0.18 – 0.74); and floating/presumably dead fish had a median survival rate of 0.18 (0.09 – 0.33). Applying these condition-specific estimates of survival to non-tagging fishery data, we estimated a discard survival rate of 0.88 (0.66 – 1.25) for 11 hook and line data sets from waters 20 to 35 m deep and 0.93 (0.71 – 1.31) for 10 trap data sets from 11 to 29 m deep. The tag-return approach using a control group with no fishery-associated trauma represents a powerful method to accurately estimate absolute discard survival of physoclistous reef species.