In recent years, the recreational contribution to the total catch of Atlantic cod (Gadus morhua) in the Gulf of Maine (GOM) has increased with recreational discards outnumbering recreational landings by 2:1. However, the discard mortality (DM) rate of cod released in the recreational fishery remains poorly understood, thus contributing to the uncertainty in stock assessments and fishery management plans. The current study examined the capture-related factors most detrimental to cod DM in the GOM recreational rod-and-reel fishery. Atlantic cod (n ¼ 640; 26.0-72.0 cm) were angled from June-October 2013 on southern Jeffreys Ledge in the western GOM using fishing gear representative of the local recreational fishery. A subset (n ¼ 136) was also tagged with pressure-sensing acoustic transmitters before being released into an acoustic receiver array (n ¼ 31) deployed to monitor survival up to 94 days. To properly model DM up to the fishery-wide level, all cod were visually assessed for capture-related injuries according to a four-level injury score index. Mean tackle-specific DM rates of 15.4 and 21.2% were estimated for bait-and jig-captured cod, respectively, with an overall 16.5% mean DM rate for the 2013 GOM recreational cod fishery. Twenty-nine cod tagged with acoustic transmitters were identified as dead, where the majority ( 90%) died within 16 h post-capture. Upon evaluation with a specifically adapted parametric survival analysis, greater incidence of mortality was attributed to the capture and handling process (rather than release) for moderately and severely injured cod. Based on the capture-related factors associated with the highest injury rates, we recommend minimizing fight and handling times, avoiding areas with small cod, educating inexperienced anglers, and favouring bait over jigs to mitigate mortality. Results will continue to inform the development of fishery management plans and enhance survival through dissemination of "best practice" techniques to fishery stakeholders.

Conservation concerns and new management policies such as the implementation of ecosystem-based approaches to fisheries management are motivating an increasing need for estimates of mortality associated with commercial fishery discards and released fish from recreational fisheries. Traditional containment studies and emerging techniques using electronic tags on fish released to the wild are producing longitudinal mortality-time data from which discard or release mortalities can be estimated, but where there may also be a need to account analytically for other sources of mortality. In this study, we present theoretical and empirical arguments for a parametric mixture-distribution model for discard mortality data. We show, analytically and using case studies for Atlantic cod (Gadus morhua), American plaice (Hippoglossoides platessoides), and winter skate (Leucoraja ocellata), how this model can easily be generalized to incorporate different characteristics of discard mortality data such as distinct capture, post-release and natural mortalities, and delayed mortality onset. In simulations over a range of conditions, the model provided reliable parameter estimates for cases involving both discard and natural mortality. These results support this modelling approach, indicating that it is well suited for data from studies in which fish are released to their natural environment. The model was found to be less reliable in simulations when there was a delay in discard mortality onset, though such an effect appears only in a minority of existing discard mortality studies. Overall, the model provides a flexible framework in which to analyse discard mortality data and to produce reliable scientific advice on discard mortality rates and possibilities for mitigation.

Empirical discard mortality rate estimates are vital to both stock assessments and fishery management, especially for stocks that experience high discard rates, such as in the recreational rod‐and‐reel fishery for Haddock Melanogrammus aeglefinus in the Gulf of Maine. The objective of the present study was to derive a fishery‐scale discard mortality rate estimate for Haddock that are captured and released in the Gulf of Maine recreational fishery by combining results of an electronic‐tagging telemetry experiment with representative fishery‐dependent survey data. Scientific personnel and industry partners collected data on a suite of biological, environmental, and technical covariates from 2,442 Haddock caught under authentic fishery scenarios during 2015. Despite being a physoclistous species, <1% of sampled Haddock were observed to die when brought onboard and only ~3% floated upon release. Postrelease fate was then monitored for 154 Haddock using passive acoustic telemetry and determined using a semiquantitative classification procedure reliant upon movement data of Haddock with known fates. The resulting data were analyzed with a parametric survival model to identify which capture‐related covariates influenced mortality. Fishing season and length‐class of Haddock were the most significant predictors of discard mortality, with increased mortality for smaller individuals caught during the autumn, possibly due to increased temperatures. Survival modeling identified that mortality from these covariates occurred primarily after release as compared with during capture and handling. By integrating survival modeling results with fishery‐dependent observations, a fishery‐scale discard mortality rate of 63% was estimated for the 2015 fishing year. Based on these findings, we recommend that fishery managers implement measures to reduce recreational Haddock discards, especially of smaller Haddock during warmer months.