A meta-analysis of immediate and delayed discard mortality of red snapper (Lutjanus campechanus)

Red snapper (Lutjanus campechanus) is an economically important fishery in the Gulf of America (formerly the Gulf of Mexico). This species is subject to discard mortality due to barotrauma. Novel discard mortality research on this species has estimated delayed mortality in addition to immediate mortality at the surface (i.e., swim or float). To determine how this combined mortality measurement changes red snapper discard mortality, we conducted a meta-analysis, combining 11 studies, with 92 distinct estimates from 34 years of research. We assessed if depth, season, release method, or region predict discard mortality. We found a significant positive relationship between depth and discard mortality and that, in the western Gulf, fishing in the summer significantly increases discard mortality compared to fishing in other seasons and regions. Analysis of studies with well-defined release method treatments revealed that venting and descending generates a 14.6% decrease in estimated release mortality compared to no barotrauma mitigation. We estimate a 31% discard mortality at 33 m, the median fishing depth of the private recreational fleet; this is more than double the discard mortality estimate generated by a previous meta-analysis based on immediate mortality alone. Given that we generated estimates from both immediate mortality and delayed mortality, we propose that these updated, higher estimates of discard mortality are more representative of the mortality experienced by this recreational fishery.Tables included here were used in analyses. The full_mort table includes all studies that addressed complete mortality of released fish, including both immediate and delayed mortality. This table is included as Table 1 in the manuscript and referenced as the 'complete mortality' dataset. The immediate mortality table here is data where researchers only quantified immediate mortality and therefore these studies were not included in the analyses of complete mortality. However, the immediate mortality table and table 1 were combined to run analyses assessing if the inclusion of delayed mortality increases overall discard mortality. The immediate mortality table is included in the supplement as Table S1 and tables S1 and 1 combined are referenced as the 'mixed mortality' dataset in the manuscript. The ReducedMort table included here is a subset of the full_mort table that removes studies where venting was not completed on all fish in the venting treatment and adds an additional laboratory study that focused on the effects of venting and descending on Red Snapper mortality. This table was included as Table S2 in the supplement and referenced as the 'release method' dataset in the manuscript.