Estimating Discard Mortality of Shallow and Deep Water Reef Fishes Using Conventional and Telemetry Tags
Sponsor: National Oceanic and Atmospheric Administration
North Carolina State University: Jeffrey Buckel
September 2014 – August 2018
The quantity and disposition of discarded fishes is a ubiquitous issue in fisheries worldwide. The South Atlantic Fishery Management Council (SAFMC) uses size and bag limits and temporal closures to manage reef fishes; thus, captured reef fish often have to be released (discarded) in order to comply with regulations. Mortality of discarded fish, while difficult to quantify, can contribute substantially to the overall rate of fishing mortality for fishes caught in waters greater than ~30 m as a result of barotrauma. Currently, managers use size limits on gray triggerfish off east coast Florida (south Atlantic) and throughout Gulf of Mexico. It is thought that size limits are an effective management tool for gray triggerfish because of assumed low discard mortality; however, this discard mortality was indirectly estimated based on behavior of surface-released gray triggerfish. Observations of fish behavior upon release may not reflect rates of discard mortality because of predation when swimming back to bottom or long-term mortality from barotrauma or hook injuries. We propose to use a novel tagging approach to directly estimate discard mortality of gray triggerfish (Balistes capriscus) in shallow waters (29-37m) of the US south Atlantic (North Carolina). A control group will be caught in traps (no hook trauma) and tagged with conventional tags on the sea floor (no barotrauma or water column predation) using SCUBA. Simultaneously, gray triggerfish in more compromised conditions (e.g., barotrauma, hook trauma) will be tagged, released at surface, and available to water-column predators when swimming back to bottom. Discard mortality will be estimated from return rates of fish in compromised conditions relative to return rates of control fish. We will control for factors such as fish size, gear, season, and depth of fishing. For deepwater (~50-175 m) reef fishes caught at the shelf break, barotrauma is thought to result in 100% discard mortality; this is problematic for fishes that have a target fishing mortality rate of zero but where catch and discarding still occur (e.g., speckled hind, warsaw groupers). Recent work on the US west coast has shown that deepwater reef fish can survive severe barotrauma if recompressed (i.e., assisted return to depth). We propose a pilot study to determine the efficacy of recompression for shelf-break reef fishes in the US south Atlantic. Deepwater reef fish will be caught with hook and line and recompressed using a descender device. Immediate condition upon release will be assessed at depth with a video camera and long-term mortality will be monitored through the use of telemetry tags, submersible fixed receivers, and an underwater glider fitted with a transceiver. Our research on shallow- and deep-water reef fishes will directly address the NOAA CRP priority need of improving estimates of discard mortality rates for reef fishes. Findings would be shared with biologists responsible for reef fish assessment. The research projects outlined in this proposal would determine robust estimates of discard mortality for gray triggerfish and determine utility of descender devices for release of deepwater reef fishes in the US south Atlantic.