Establishing Stock Status Determination Criteria for Fisheries with High Discards and Uncertain Recruitment
2018
Goethel, Daniel R. | Smith, Matthew W. | Cass‐Calay, Shannon L. | Porch, Clay E.
Maximum sustainable yield (MSY)‐based reference points are often prescribed by national and international laws as the basis for catch limits (e.g., the Magnuson–Stevens Reauthorization Act in the United States). However, MSY is highly dependent on the assumed selectivity pattern and catch allocation of the fisheries. The addition of bycatch fleets or mortality from discarding further complicates MSY calculations, and no prescribed approach has been agreed upon for including complex fleet dynamics in dynamic pool models. Using the Gulf of Mexico Red Snapper Lutjanus campechanus fishery as an example, we demonstrate the various ways that MSY can be computed when multiple fleets and bycatch fisheries exist, and we illustrate the tradeoffs that occur between yield and spawning stock biomass (SSB). Presenting the full array of alternative MSY proxies, however, can lead to subjective decision making that may diminish the value of scientific advice by encouraging the maximization of yield at the expense of maintaining stocks within safe biological limits. We propose that the spawning potential ratio (SPR) associated with the global (theoretical maximum) MSY can be utilized as a reasonable proxy in most fishery applications. The yield streams required to achieve SPRMSY can then be calculated conditional on extant selectivity patterns and bycatch levels. Our approach utilizes the inherently sustainable SSB associated with the global MSY as a rebuilding target while limiting disruption to the fishery by accounting for current fleet dynamics and avoiding unsustainable proxies that may result when bycatch or discard rates are high.
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