Estimates of Red Drum Mortality via Acoustic Telemetry

Subadult (age< 3) Red Drum Sciaenops ocellatus support a valuable recreational fishery, and mortality estimates for young Red Drum are needed for proper management. To obtain these estimates, age-1 and age-2 Red Drum were implanted with acoustic transmitters and external Floy tags in two coastal Alabama rivers (Fowl and Dog rivers). Fates of tagged fish were inferred from stationary receiver detections and active relocations over 1 year. These fates were used in a Bayesian multistate model to estimate instantaneous monthly and annual mortality and emigration rates for each river and overall from both rivers. Instantaneous monthly fishing mortality (F) ranged from 0.001 to 0.112 (annual F= 0.414) in Dog River, from 0.001 to 0.126 in Fowl River (annual F= 0.309), and was 0.001–0.054 (annual F= 0.337) overall. Instantaneous monthly natural mortality (M) ranged from 0.001 to 0.002 (annual M= 0.069) in Dog River, from 0.001 to 0.036 (annual M= 0.178) in Fowl River, and from 0.001 to 0.017 (annual M= 0.090) overall. The overall annual estimate of instantaneous total mortality (Z) was 0.435. The median escapement percentage was estimated at 36.3% (95% posterior credible interval= 19.5–56.0%) using M and Z from the overall model. Unfortunately, the error on this estimate was large and inconclusive as to whether the 30% escapement goal for juvenile Red Drum to the adult population from Dog and Fowl rivers is being met. Monthly residency estimates were typically greater than 0.90, and overall annual residency was estimated at 0.716. Fishing mortality estimates from the current study are higher than recent catch curve estimates that did not include young Red Drum. These results demonstrate that young Red Drum need to be accounted for when generating mortality estimates and provide needed data for the Red Drum recreational fishery. Mortality of fishes is an essential piece of information for proper fisheries management, stock assessment, and the continued persistence of valuable fish stocks in response to variable fishing and environmental pressures (Hilborn and Walters 1992; Harris and Hightower 2016; Hightower and Harris 2017). Fish mortality rates can be obtained using a variety of techniques, such as catch curve analysis (Ricker 1975; Hilborn and Walters 1992), longevity estimators (Hoenig 1983; Hewitt and Hoenig 2005; Then et al. 2015), and/or mark–recapture models (Pine et al. 2003, 2013). Total mortality (Z) must be divided into natural mortality (M) and fishing mortality (F) for exploited species, and using telemetry studies as extensions of traditional mark–recapture designs is one way to obtain these mortality components (Hightower et al. 2001; Hightower and Harris 2017). This method can provide benefits over traditional tagging studies because (1) fish do not have to be physically recaptured and (2) multiple fish fates, including M and F, may be inferred from detection data (Hightower et al. 2001; Hightower and Harris 2017). Furthermore, mortality estimation across multiple spatial and temporal scales may be possible, elucidating seasonal, regional, and environmental drivers of mortality (Bacheler et al. 2009a; Ellis et al. 2017). Subject editor: Jeffrey A. Buckel, North Carolina State University, Morehead City *Corresponding author: thomas.nelson@noaa.gov Received July 30, 2019; accepted January 21, 2020 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Marine and Coastal Fisheries: Dynamics, Management, and Ecosystem Science 12:78–97, 2020 © 2020 The Authors. Marine and Coastal Fisheries published by Wiley Periodicals, Inc. on behalf of American Fisheries Society. ISSN: 1942-5120 online DOI: 10.1002/mcf2.10110