ESR prepress abstract  -  DOI: https://doi.org/10.3354/esr00870

Release mortality of endangered Warsaw grouper Hyporthodus nigritus: a state-space model applied to capture-recapture data from a shallow site off the Atlantic coast of Florida

Kyle W. Shertzer*, Nathan M. Bacheler, G. Todd Kellison, John Fieberg, Robert K. Wiggers

*Email: Kyle.Shertzer@noaa.gov

ABSTRACT: Warsaw grouper Hyporthodus nigritus is a large-bodied, deep-water, demersal fish species listed on the IUCN Red List as Critically Endangered. In the United States, harvest of Warsaw grouper in recent decades has been heavily limited or prohibited. However, Warsaw grouper is part of a multispecies snapper-grouper fishery, making them vulnerable to incidental capture (and release) as bycatch, even if not targeted for harvest. Therefore, release mortality is a primary concern for the recovery of this endangered species, especially given the potential barotraumatic effects of capture. Here, we utilize a long-term (11 yr) data set containing capture-recapture information on tagged Warsaw grouper collected through a citizen-science program, the South Carolina Marine Game Fish Tagging Program. We fit a state-space model to these data that accounts for—and provides estimates of—release mortality as a function of length. These estimates quantify the combined effect of immediate and delayed mortality. We found that release mortality increased with length, from expected values lower than 10% to values exceeding 70%. At a total length of 700 mm, near our observed mean, the expected release mortality was 34% (95% credible interval of 3%–57%). In general, release mortality estimates were lower than might be assumed (~100%) for a deep-water grouper. We suggest possible explanations for this result, such as the relatively shallow depth (~49 m) of this study and the careful treatment of released fish, and conclude by discussing implications for future research and conservation.