The objectives of this study are to model the affects and implications of recent advances in discard mortality mitigation of Gulf of Mexico (GOM) reef fish fisheries. I propose to use red snapper (Lutjanus campechanus) as a model species to estimate the effects of reductions in recreational discard mortality on stock dynamics, productivity, and potential fishery yield. Red snapper will serve as a model given the extensive data on discard mortality estimates, the contentious nature of red snapper assessment and management, and the fact that currently approximately 1.5 fish are killed in the recreational fishery for every 1 fish landed (SEDAR 2015). Therefore, reductions in discard mortality in this fishery promise to have meaningful implications for stock assessment and management. The results will provide specific advice to the Gulf Council on the effects of reduced discard mortality and alternate management approaches on the landings, size of harvested fish, spawning stock biomass, and season length of the red snapper fishery. Management approaches will include requiring the use of descender devices to reduce the mortality of discarded fish and restrictions (complete or partial) on harvesting fish outside minimum and maximum sizes (harvest slots). The results will have meaningful implications for stock assessment and management of red snapper, as well as other reef fishes, such as other snappers, groupers, and jacks. In addition, the results will be pertinent to other regional and national fisheries for which discard mortality impedes management efficiency.
This study will apply the results of current research that I am performing on descender devices (Patterson and Calay research in progress funded by the NMFS Cooperative Research Program in collaboration with the Ocean Tracking Network, Halifax, Nova Scotia) to stock dynamics and management recommendations for GOM recreational reef fish fisheries. This current research uses a novel largescale offshore acoustic telemetry array and external acoustic-tagged red snapper. The effect of release method (released at the surface or returned to the bottom with a descender device) on discard mortality will be assessed. Updated discard mortality estimates (both with and without the use of descender devices) will be examined alone and combined with potential harvest slot management scenarios within the red snapper Stock Synthesis III assessment model (Methot 2012; SEDAR 2015). Red snapper will serve as the initial model species, after which the results may be applied to several other species of GOM reef fish, such as other snappers, groupers, and jacks.
Reductions in red snapper discard mortality due to descender device utilization will be used to modify release mortality estimates in the base model run of the most recent stock assessment of red snapper in Stock Synthesis III, which in turn will be utilized to examine implications of study results for estimates of stock productivity, rebuilding timelines, and annual overfishing limits (Methot 2012, SEDAR 2013). Stock Synthesis III is a statistical framework of models, implemented in AD Model Builder (Fournier et al. 2012), which accepts a variety of input fisheries data and estimates values and error for common fisheries stock assessment parameters such as projected biomass, recruitment, landings, and fishing mortality (Methot 2012). Dr. Shannon Cass-Calay, NMFS Branch Chief supervising stock assessment of GOM reef fish, will collaborate on developing the best methods to integrate the descender device research into the red snapper stock assessment in Stock Synthesis.
One potential approach is to calculate savings in total removals (total fishery kill) resulting from decreased discard mortality. The most recent red snapper benchmark assessment assumed a discard mortality rate of 22% in the western GOM and 21% in the eastern GOM (SEDAR 2013). Updated discard mortality from the initial investigation into the efficacy of descender devices will be used to redefined the discard mortality parameters in the SEDAR (2013) base model (while assuming that discard mortality is constant as a function of fish length). Both the status quo scenario (fish are released at the surface) and required descender device use scenarios will be investigated.
The addition of harvest slot regulations to reduced discard mortality would modify retention at length leading to changes in landings and discards. The current version of Stock Synthesis assumes that only a minimum size limit is regulated for in a fishery, hence the retention at length (L) is a three parameter (P1, P2, P3) logistic function that cannot be modified to other forms (eq. 5, Methot 2012, Chagaris et al. 2015). A retention function to describe a fishery managed under a slot limit [minimum and maximum (Slotmax) size limits] might include a dome-shaped double logistic function which contains three additional parameters (eqs. 6a and 6b).
In the GOM, recreational fishers discard the majority of catch of several reef fish species including red snapper, gray triggerfish (Balistes capriscus), gag grouper (Mycteroperca microlepis), greater amberjack (Seriola dumerili), and sharks (Sauls 2012; Sauls and Cernak 2013; Garner and Patterson 2015). Discarded fish may suffer immediate or delayed mortality, thus diminishing benefits of release and contributing to wasted harvest and the national bycatch problem (Bartholomew and Bohnsack 2005; Rummer 2005; Strelcheck and Hood 2007).
Recent research indicates that technological innovations and improved practices, such as the use of descender devices, may effectively increase the survival of fish that are released by recreational fishers (Butcher et al. 2012; NOAA 2013; PFMC 2013; Benaka et al. 2014; Heberer 2015). Increased discard survival would transform a percentage of the total kill in the recreational fishery to landed catch (versus dead discards), thus allowing for increased recreational harvest and extended fishing seasons. Increased discard survival would remove the current impediment to utilizing harvest slots in reef fish management, including the recreational red snapper fishery. Initial simulations suggest that recreational slot limits would be a much more effective management tool that would in turn impart several benefits to the recreational fishery, such as increased quota size (landed catch), season length, and spawning stock biomass (Farmer et al. 2014). In the case of red snapper (one of the GOM's most economically valuable fishery resources), this would be advantageous given that the season for private vessels in Federal waters lasted for only 11 days in 2015 (Strelcheck and Hood 2007; NOAA 2015).